- 1 Components
- 2 DL/I Terminology
- 3 DATABASE HIERARCHY CHART
- 4 DESIGNING AND DESCRIBING THE DATABASE TO IMS / DL - I
- 5 APPLICATION / LOGICAL DATA-STRUCTURE (PSB)
- 6 DL / I PROGRAMMING CONSIDERATIONS
- 6.1 WORKING STORAGE SECTION
- 6.2 LINKAGE SECTION
- 6.3 PROCEDURE DIVISION
- 6.4 DL/I CALLS
- 6.5 Segment Search Argument:
- 6.6 SSA STRUCTURE:
- 6.7 SSA TYPES:
- 6.8 CALL TYPES
- 6.9 DATABASE DL/I CALLS
- 6.10 RELATIONAL OPERATORS
- 6.11 HOSPITAL DATABASE SEGMENT OCCURRENCE CHART
- 6.12 RANDOM RETRIEVAL USING GU CALL
- 6.13 SEQUENTIAL RETRIEVAL USING GN CALL
- 6.14 GN calls without SSA's (unqualified GN calls)
- 6.15 GN call with Unqualified SSA's (Qualified GN call)
- 6.16 GN call with Qualified SSA's (Qualified GN Call)
- 6.17 GN Calls - STATUS CODES
- 6.18 SEQUENTIAL RETRIEVAL USING GNP CALL
- 6.19 GNP calls without SSA's (Unqualified GNP call)
- 6.20 GNP call with Unqualified SSA's (Qualified GNP call)
- 6.21 GNP call with Qualified SSA's (Qualified GNP call)
- 6.22 GNP Calls - STATUS CODE
- 7 UPDATING AND DELETING SEGMENTS
- 8 INSERTING SEGMENTS INTO AN EXISTING DATABASE
- 9 DBD INSERT RULES
- 10 ADVANCED DATABASE PROCESSING
- 10.1 BOOLEAN SSA STATEMENTS
- 10.2 SSA'S USING COMMAND CODES
- 10.3 F COMMAND CODE
- 10.4 L COMAMND CODE
- 10.5 D COMMAND CODE & N COMMAND CODE
- 10.6 RETRIEVING AND REPLACING WITHOUT COMMAND CODE
- 10.7 C COMMAND CODE
- 10.8 Q COMMAND CODE
- 10.9 U AND V COMMAND CODES
- 10.10 P COMMAND CODE
- 10.11 NULL COMMAND CODE
- 10.12 MULTIPLE POSITIONING WITHIN THE PCB
- 10.13 MULTIPLE PCB's IN A PSB
- 10.14 LOGICAL DATABASES
- 10.15 LOGICAL RELATIONSHIPS
- 10.16 DBDGEN'S FOR PHYSICAL DATABASE WITH LOGICAL RELATIONSHIPS
- 10.17 PSBGEN USING LOGICAL DATABASE
- 10.18 IMS SYSTEM DATASETS
- 11 APPENDIX - A
- 12 APPENDIX - B
- 13 APPENDIX - C
- This is the latest version
- Consists of a DL/I component that interface with the Database
- Consists of Data communication component that interface with the users at remote terminals
- Runs under operating system MVS/OS/VS1/OS/VS2
- Runs under operating system OS/VS1/OS/VS2
- Consists of a DL/I component that interface with the Database
- Consists of a Data Communication component that interface with the users at remote terminals
DL/I - DOS/VS
- Runs under operating system DOS/VSE
- Consists only of interface with the database
Five Components of IMS Environment
Database Management System
- This is the heart of IMS subsystem
- Shared by many concurrent tasks
- Data is stored in DASD
- Application Programs access data by making DL/I calls
DL/I (Data Language / I )
- Is a set of program modules interfacing database and application program
- The modules use standard operating system access methods and a set of specialized access methods to handle data transfers to and from the database
- This is an Interface Language used by the Application Program
DL/I Control Blocks
- There are two main DL/I control blocks, one describing the database structure, the other identifying how the database may be accessed by the program
- They are Database Descriptor (DBD), and Program Communication Block (PCB)
- The Database Administration Group normally maintains these control blocks.
- DBD describes the physical structure of a database as well as the way in which it is stored on the DASD and the way it is accessed
- PSB describes the Logical Structure of a Database as a particular application program views it. It identifies which pieces of data a program is allowed to access and the kinds of functions (operations) it can perform on each collection of data.
- These are designed and coded by the programmers
- The programs use a standard DL/I interface to other IMS components
- DL/I Application Programs use standard CALL statements with a parameter list to communicate with IMS.
- Programs may be written in COBOL, PL/I. ASM
- Is a set of program modules that allow the program to communicate with remote terminals
- Programs communicate with terminals through a Standard Interface Language using CALL statements with a parameter list.
Assume, the general information we store in the HOSPITAL Database is:
- HOSPITAL information
- WARDS & ROOMS information in each hospital
- PATIENTS information in each WARD
- PATIENTS information in each WARD
- SPECIAL FACILITIES information in each hospital
- WARDS & ROOMS information in each hospital
COBOL structure for Hospital Database is: -
01 HOSPITAL 05 HOSPNAME PIC X(20) Unique Key 05 Hosp-Address PIC X(30) 05 Hosp-Phone PIC X(10) 01 WARD 05 WARDNO PIC X(2) Unique Key 05 Total-Rooms PIC X(3) 05 Total-Beds PIC X(3) 05 BEDAVAIL PIC X(3) Search 05 WARDTYPE PIC X(20) Search 01 PATIENT 05 PATNAME PIC X(20) Search 05 Patient-Address PIC X(30) 05 Patient-Phone PIC X(10) 05 BEDIDENT PIC X(4) Unique Key 05 DATEADMT PIC X(6) Search 01 SYMPTOM 05 DIAGNOSE PIC X(20) Search 05 SYMPDATE PIC X(6) Non-Unique Key 05 Treat-Description PIC X(20) 05 Symp-Doctor PIC X(20) 05 Symp-Doc-Phone PIC X(10) 01 TREATMNT 05 TRTYPE PIC X(20) Search 05 TRDATE PIC X(6) Non-Unique Key 05 Medicine-Type PIC X(20) 05 Diet-Comment PIC X(30) 05 Surgery-Flag PIC X 05 Surgery-Date PIC X(6) 05 Surgery-Comment PIC X(30) 01 DOCTOR 05 DOCTNAME PIC X(20) Search 05 Doct-Address PIC X(30) 05 Doct-Phone PIC X(10) 05 SPECIALT PIC X(20) Search 01 FACILITY 05 FACTYPE PIC X(20) Search 05 Tot-Facility PIC X(3) 05 FACAVAIL PIC X(3) Search
HIERARCHICAL STRUCTURE FOR HOSPITAL DATABASE
LEVEL 1 (ROOT)
- IMS maintains an Inverted Tree Structure starting with the Root Segment by ensuring that no segment has more than one parent
- Each box represents a segment name of up to 8 characters at each level called as a Segment Type
- The above diagram of Hospital Database is called as an Database Hierarchy Chart
- The Hierarchy can go up to fifteen levels down
- The Hierarchy can represent up to 255 segment types
DATABASE HIERARCHY CHART
- It is the smallest unit of information DL/I handles
- Within each segment are one or more data fields
- Each 01 level data name defines one of the segments in the Hospital Database
- Each 03 level data name defines one of the fields within a segment
- If an application program requires information only about a segment, it does not even have to know that the other segments exists, or what their relationships are within the database
- Also known as a Segment Type
- Can have up to 255 segment types in a Database record, and up to 15 segment types in any one hierarchical path.
- The terms Parent and child are used to describe the relationships between segment types within a database
- A segment that has one or more segments directly below it in the hierarchy is called a PARENT segment
- A segment that has a segment directly above it in the hierarchy is called a CHILD segment
- Parent and Child segments are relative terms which depends upon which portion of the database hierarchy is under focus of discussion
- A child segment is also called as a DEPENDENT segment
- The concept of Dependent segments extends more than one level in the hierarchy
- If a parent occurrence is deleted, so are all its children
SEGMENT (TWINS) - Multiple Occurrence
- All occurrences of a particular segment type under a single parent segment occurrence are called TWINS
- The set of all Twins dependent on a particular parent is often referred to as a TWIN CHAIN
- For example :
- All the symptom occurrences for a particular patient are called TWINS in a TWIN CHAIN
- Segments are always accessed and retrieved along the Hierarchical Paths
- A path is a route line that Begins at the Root segment, travels through the segments at Intermediate levels in the hierarchy and Ends at a segment in the Bottom of the hierarchy
- There are Four paths in the Hospital Database such as
HOSPITAL HOSPITAL HOSPITAL HOSPITAL WARD WARD WARD FACILITY PATIENT PATIENT PATIENT SYMPTOM TREATMENT DOCTOR
- A database consists of all the Root Segment occurrences along with their dependants
- Is normally shared by Multiple Applications
- A database record consists of a SINGLE occurrence of the ROOT segment and all of its dependent segments
- In the hospital database, a single record consist of a single occurrence of the HOSPITAL segment and all of the segment occurrences below it that belong to a particular hospital in the hierarchy
DESIGNING AND DESCRIBING THE DATABASE TO IMS / DL - I
- A number of factors must be considered by DBA while designing the database
- Questions about database design, that a programmer is concerned with are
- Segment names a program may access
- Various fields formats within the accessed segments
- Names and formats of the fields used for search
- Hierarchical relationships of the accessed segments
- Processing permissions on the accessed segments
- A segment may not have any search or key fields defined on it.
KEY OR SEQUENCED FIELDS
- The Database Designer has to decide not only the contents in each segment, but also what content with each segment would be known to IMS as key fields and search fields
- A key or sequenced field is a field with the segment that DL/I uses to maintain segments in the Ascending Sequence
- Only a single field within each segment may be designated as a key or sequence field
- Key field in a segment is OPTIONAL
- Key field may be designated as UNIQUE or NON-UNIQUE
- A ROOT segment is required to have a UNIQUE key field
ADDITIONAL SEARCH FIELDS
- A field on which the segments are not sequenced, but contents of which can be used to perform a SEARCH in the database is called as well as designated as a SEARCH field for a segment
- Up to 255 search fields can be identified in a segment including the KEY field
- Any data item or a combination of contingents data items can be designated as a search field
DATABASE DESCRIPTION (DBD)
- Once segments are defined, the Hierarchical Structure decided upon, the key and search fields identified, DBA can communicate this design of Database to DL/I
- Accordingly a CONTROL BLOCK for Database called DBD is created in a DL/I library, which describes the physical structure of a database to IMS
- DBD is created by a process called DBD Generation or DBDGEN, wherein DBA codes a series of Control statements. The process is performed only once for database unless the physical structure of database undergoes a change.
- DBDGEN control statements are Assembler Language Macros supplied by IBM and submitted via JCL invoking a catalogued procedure called DBDGEN producing an OBJECT module.
- Macros are stored in Maclib and load modules are stored in DBDLIB, which is the DBD itself and ready for loading
- The Hospital database DBD control statements will look like
PRINT NOGEN DBD NAME=HOSPDBD, ACCESS=HISAM DATASET DD1=HOPSET, OVFLW=HOSPFLW, DEVICE=3330 SEGM NAME=HOSPITAL, PARENT=0, BYTES=60 FIELD NAME=(HOSPNAME,SEQ,U), BYTES=20, START=1, TYPE=C SEGM NAME=WARD, PARENT=HOSPITAL, BYTES=31 FIELD NAME=(WARDNO,SEQ,U), BYTES=2, START=1, TYPE=C FIELD NAME=BEDAVAIL, BYTES=3, START=9, TYPE=C FIELD NAME=WARDTYPE, BYTES=20, START=12, TYPE=C SEGM NAME=PATIENT, PARENT=WARD, BYTES=70 FIELD NAME=(BEDIDENT,SEQ,U), BYTES=4, START=61, TYPE=C FIELD NAME=PATNAME, BYTES=20, START=1, TYPE=C FIELD NAME=DATEADMT, BYTES=6, START=65, TYPE=C SEGM NAME=SYMPTOM, PARENT=PATIENT, BYTES=76 FIELD NAME=(SYMPDATE,SEQ), BYTES=6, START=21, TYPE=C FIELD NAME=DIAGNOSE, BYTES=20, START=1, TYPE=C SEGM NAME=TREATMNT, PARENT=PATIENT, BYTES=113 FIELD NAME=(TRDATE,SEQ), BYTES=6, START=21, TYPE=C FIELD NAME=TRTYPE, BYTES=20, START=1, TYPE=C SEGM NAME=DOCTOR, PARENT=PATIENT, BYTES=80 FIELD NAME=DOCTNAME, BYTES=20, START=1, TYPE=C FIELD NAME=SPECIALT, BYTES=20, START=61, TYPE=C SEGM NAME=FACILITY, PARENT=HOSPITAL, BYTES=26 FIELD NAME=FACTYPE, BYTES=20, START=1, TYPE=C FIELD NAME=FACAVAIL, BYTES=3, START=24, TYPE=C DBDGEN FINISH END
Hospital Database DBDGEN macros
- PRINT NOGEN
- Causes the assembler to suppress the listings of machine instructions generated by each macro
- Apart from describing the Physical Structure and Interdependency of segments in Database, it also names the DBD and the Access method that will be used by DL/I for data manipulation
- Specifies the names of files used to store the data. HISAM database requires two files and their names must be included in the program execution JCL accessing the database. Device specifies the device type in which the allocated files will store the segment data
- Each SEGM statement names and describes one segment type that will make up the database. Name operand names the segment type. Parent operand names the parent of each segment type thereby defining the Hierarchical Structure of a database. A root segment is identified by the absence of a Parent operand or Parent=0. The SEGM statements are coded in the hierarchical sequence of the segment types, that is, from TOP to BOTTOM and from LEFT to RIGHT. The Bytes operand specifies the segment length in terms of bytes.
- Each field statement names and describes the key and search fields for a segment. NAME parameter contains from one to three positional sub-parameters. The first sub-parameter names the key or search field. If it is the only sub-parameter coded, the field will be a search field. If SEQ is coded as the second sub-parameter, the field will be a key field, and the occurrences will be sequenced in Ascending order. This is optional. If specified, only one key field is allowed per SEGM statement. If U is coded as the third sub-parameter, the field is a UNIQUE sequence field unless M is specified for Multiple value in the field. If neither 'U' nor 'M' is specified when SEQ is coded, the sequence field is taken to be unique. A unique sequence field is required for the root segment in HISAM and HIDAM methods. The START operand tells the starting byte position of the key or search field relative to the beginning of the segment. The BYTES operand tells the field length in bytes. TYPE operand tells the data type of field, accordingly C specifies a character field of alphanumeric type, P specifies a packed Decimal numeric type. C is the default data type. FIELD statement for the sequence field, if there is one, must be the first such statement for the segment.
- This statement ends the SEGM and FIELD definitions for the DBD
- This statement causes the assembler to set a non-zero condition code if errors are encountered during the assembly process.
- This statement marks the end-of-data to the assembler
- That the names of the Segments key & search fields that match in the COBOL Structure with that of the names used in the DBD is not an IMS requirement.
APPLICATION / LOGICAL DATA-STRUCTURE (PSB)
- Logical Data Structure is a term used to refer to a group of segments that an application program may access. To the application program, the logical data structure is the database
- The DBA defines the logical data structure by creating a Control Block called a Program Specification Block or PSB.
- PSB is created with a process called PSB generation or PSBGEN, very similar to the DBDGEN process; wherein DBA codes a series of control statements
- PSBGEN control statements are Assembler Language Macros supplied by IBM and submitted via JCL invoking a catalogue procedure called PSBGEN producing an OBJECT module.
- Macros are stored in Maclib and Load modules are stored in PSBLIB, which is the PSB itself and ready for loading
- The PSB control statements for a Retrieved program will look as below.
- Each PSB consists of one or more control blocks called Program Communication Blocks or PCB's. Each PCB within a PSB defines exactly one Logical Data Structure
- All the PCB's within a single PSB are collectively known as an Application Data Structure
- It is possible that more than one program may share a single PSB, however, no program can use more than one PSB in a single execution
- The Logical Data Structures defines all the segments that an application program may access using that PSB
PCB TYPE=DB, NAME=HOSPDBD, KEYLEN=26 SENSEG NAME=HOSPITAL, PARENT=0, PROCOPT=K SENSEG NAME=WARD, PARENT=HOSPITAL, PROCOPT=K SENSEG NAME=PATIENT, PARENT=WARD, PROCOPT=G PSBGEN LANG=COBOL, PSBNAME=PATRETRV END
Hospital Database PSBGEN macros
- This is the first statement in a PSB. It marks the beginning of one Program Communication Block (PCB). TYPE operand specifies that this is a Database PCB as opposed to a terminal PCB. NAME operand names the DBD for which the PCB is created; KEYLEN specifies the length of the key feedback area. When the program retrieves a segment using DL/I GET, IMS not only fetches the requested segment but also places a fully concatenated key into the key feedback area of PCB mask which consists of the concatenation of the sequence field values of all the segments in the hierarchical path from the root down to the retrieved segment
- These statements identify the segments in the database that this application program is sensitive to. NAME operand names a segment that is sensitive and must be the same as the name coded in the NAME operand in the SEGM statement in the DBD. PARENT operand names a segment that is parent to the SENSEG name. This operand identifies the hierarchical structure of this Logical Data Structure as supported by the DBD. The PROCOPT operand is optional. It stands for the processing options and identifies the processing types that may be performed on each segment by the application program. 'K' means that the segment is key sensitive only. The application may use the segment only to gain access to the segments below it in the hierarchy and not to access any data within it. If a sensitive segment is not key sensitive, it is data sensitive i.e. when PROCOPT = G, I, R or D or A. Any or all of GIRD may be specified in any order.
- Identifies the language of the program that will use the PSB and gives a name to PSB coded at the end.
- The sensitive segments must be specified in the hierarchical sequence as in DBD. Such as Top to Bottom, Left to Right
- If the PROCOPT operand value is same for all the entries of SENSEG within a PCB then you may specify PROCOPT operand in the PCB statement itself instead of in each SENSEG. If PROCOPT operand is specified in both, the SENSEG entry overrides the PCB entry. However, the PROCOPT = L (Load - to create the initial version of the database) may be specified only in the PCB statement which cannot be overridden. Also, the PROCOPT = K (Key sensitivity) may be specified only in the SENSEG statement.
- For Field Level sensitivity within a sensitive segment include the statement SENDFLD immediately following the statement SENSEG as
SENDFLD NAME = fieldname, START = position SENDFLD NAME = fieldname START = position
Name and the Field Length are inherited from DBD. The order in which field names are specified is irrelevant
//RETRIEVE EXEC PGM=DFSRRC00, PARM=DLI, PATRETRV //STEPLIB DD DSN=IMSVS.RESLIB, DISP=SHR // DD DSN=IMSVS.PGMLIB, DISP=SHR //IMS DD DSN=IMSVS.PSBLIB, DISP=SHR // DD DSN=IMSVS.DBDLIB, DISP=SHR //SYSUDUMP DD SYSOUT=A //HOSPSET DD DSN=IMS.VSAM.HOSPSET, DISP=OLD //HOSPFLW DD DSN=IMS.VSA.HOSPFLW, DISP=OLD //OUTPUT DD SYSOUT=A //INPUT DD A ------------------------------------- ------------------------------------- ------------------------------------- (INPUT TRANSACTIONS) ------------------------------------- -------------------------------------
- Under IMS, the Batch Initialization Module DFSRRC00 is invoked via JCL which in turn loads the application program and the DL/I modules required to service it.
- Under IMS, a batch DL/I program executes as a sub-program of DL/I even though the program invokes DL/I services by issuing DL/I calls. The program and the DL/I modules execute together
- DFSRRC00 is the DL/I load module called as the Region Controller
- A convention, which is required for IMS-DC programs and optional for IMS-DB batch programs, is that the Load module name and the PSB name should be the same. They are specified in the PARM operand of EXEC statement. If the program name and PSB name is different, DL/I allows to specify both names in the PARM operand.
- With the help of NAME operand in the PCB statement of PSB, IMS system loads into memory the DBD of Database required
- With the help of DD names in the DATASET statement of DBD, the execution JCL describes the physical file in the DD statements for the Database storage
- The other DD statements are required by DL/I
DL / I PROGRAMMING CONSIDERATIONS
- The application program is treated as a subroutine of DL/I and standard subroutine Linkages and Parameter lists are used to connect the application program to the DL/I modules that passes control to it.
- When DL/I links to the application program, it passes to the program a parameter list containing the addresses of the PCB's in the PSB
WORKING STORAGE SECTION
- The DL/I Function Code variables are copied here
- The SSA'S (Segment Search Arguments) for segment retrievals are defined here
- The structure in COBOL for various segments within the database are declared here, usually through a COPY statement
- PCB masks for the PCB's passed to the program by DL/I is coded here
- The data names describe the data areas in the PCB mask for the PCB's that DL/I loaded
- Must for every DL/I program since PCB is a DL/I control block that is loaded into memory by DL/I before the program is executed.
- When a DL/I call is issued, the PCB mask must be specified to indicate which PCB (database) in the PSB is to be used to process the call
- DL/I updates the PCB mask with the execution results after every DL/I call
The structure of a PCB mask is
01 PCB-MASK 05 DBDNAME PIC X(8) 05 LEVEL-NUMBER PIC X(2) 05 STATUS-CODE PIC X(2) 05 PROC-OPTIONS PIC X(4) 05 JCB-ADDRESS PIC X(4) 05 SEGMENT-NAME PIC X(8) 05 KEY-LENGTH PIC S9(5) COMP 05 NUMBRE-SEGS PIC S9(5) COMP 05 KEY-FEEDBACK 07 HOSPNAME-KEY PIC X(20) 07 WARDNO-KEY PIC X(2) 07 BEDIDENT-KEY PC X(4) PROCEDURE DIVISION ENTRY 'DLITCBL' USING PCB-MASK
- The entry code accomplishes three things in a program written in COBOL. They are
- It gives a standard DL/I name to the entry point of any COBOL - DL/I program which must be DLITCBL
- It hooks the program to the PCB through the USING clause of the ENTRY statement
- The sequence of PCB masks specified in the ENTRY statement must be identical to the sequence of their corresponding PCB's in the PSB. Although the order of PCB masks in the Linkage Section does not matter.
- The execution of a program terminates with a GOBACK statement because all DL/I programs are sub routines of DL/I. Therefore, do not use STOP-RUN
- The ENTRY statement provides a mechanism for DL/I to transfer control to the application program
- Calls to DL/I are made using a DL/I interface language
- IMS services are requested via DL/I calls having a standard format
- The Language Components are
- The call statement parameter list
- The formats of the data items specified in that list
- DL/I calls can be imbed in COBOL, DL/I or Assembler
- The entry point name in the CALL statement is 'CBLTDLI' the name used whenever a DL/I service is requested in a COBOL program
- The general command format is
CALL 'CBLTDLI' USING function code PCB mask I-O Area SSA's
- This is the first parameter in the list. It names a four byte function code for the service requested from DL/I such as Insert, Update, Delete, and Browse of database. A function table Copybook called DLI CALLS is copied in the application program using the command COPY DLI CALLS
PCB Mask Name:
- This is the second parameter in the list. It names the PCB mask of the Database this DL/I call in use.
- After execution of the DL/I call, IMS will load the PCB mask specified in the call with the execution result.
- The fields in the PCB mask structure are as follows
DBDNAME The DBD name of the database the call tried to manipulate upto 8 characters long
LEVEL NUMBER The level number of the last segment encountered which satisfied a level of the call. When the retrieval is successfully completed, the level number of the retrieval segment is placed in this field. The level number is two bytes, Right Justified, Decimal Number field
STATUS CODE After the execution of every DL/I call, this field is updated with a two-character code, which indicates the result of call execution. If the execution is successful this field is blank else appropriate status code for the service requested will be returned by DL/I PROCESSING This is a four byte left justified field in which the processing
OPTIONS Options for the type of calls allowed in a program for the database specified in the PCB statement of PSB is returned by DL/I. The processing options are specified by PROCOPT operand.
JCB ADDRESS This is a four byte field reserved for DL/I containing a four byte address of an Internal Control Block called the JCB. An area within JCB keeps track of the most recent calls.
SEGMENT NAME This is an eight-byte field with the name of the last segment encountered which satisfied a level of the call. When the call execution is successful, the name of the retrieved segment is updated here, else the name of the segment along the path that satisfied the search condition.
KEY LENGTH This is a field giving the length in bytes of the concatenated key of all the segments along the key values of all the segments along the retrieval path string together. This is a four-byte field.
NUMBER OF This field contains the number of the segment types within SEGMENTS the database to which the application program is sensitive to as specified in the SENSEG statements of the PCB in the PSB. This is a four-byte field.
KEY FEEDBACK Contains the actual concatenated key values of all the AREA segments along the retrieval path upto the last segment encountered which satisfied a level of the call. The key fields are positioned from Left to Right, beginning with the Root segment key value. This field is a variable field structure depending upon the segments of a database. Rests of the fields have a standard format and fixed length. This field contains the key values or even though the segment may be retrieved using a search field. A segment with NO KEY field will skip that level in the concatenated key.
INPUT-OUTPUT This is the third parameter in the list. This area is used by AREA DL/I to put a retrieved segment or by the application program to store the date of a segment prior to addition or updation. If a single segment occurrence is received, inserted or updated this area should be the segment layout area. The I-O area must be large enough to contain the data of the largest segment type. After determining which segment is retrieved move the segment contents to an area describing it. Another option is to use the REDEFINES clause to describe each segment type in the Hierarchy path.
- Note The first three parameters in the List Function Code, PCB address, I-O area are Required when retrieving a segment using DL/I call. Optionally you can also specify a Segment Search Argument to further describe and qualify the retrieval call.
Segment Search Argument:
This is the fourth parameter in the list. This is optional. Whenever specified, DL/I uses it to narrow the field of search to a particular segment type or to a particular segment occurrence to be manipulated at each level of database. There can be maximum of 1 SSA per level upto 15 SSA's for each database. If SSA is not used for any level, DL/I will follow the rules to calculate the default SSA.
There are calls with three options:
- Without SSA's
- With unqualified SSA's
- With Fully Qualified SSA's
- With combination of Qualified & Unqualified SSA's
For example, to retrieve a specific patient in a ward of a hospital will require 3 SSA's to be coded in the card.
WORKING-STORAGE SECTION 01 PATIENT-SEGMENT 05 ------ 05 ------ 05 ------ 01 HOSPITAL-SSA 05 FILLER PIC X(19) VALUE 'HOSPITAL (HOSPNAME = ' 05 HOSPNAME PIC X(20) 05 FILLER PIC X VALUE ')' 01 WARD-SSA 05 FILLER PIC X (19) VALUE 'WARD (WARDNO =' 05 WARD NO PIC X(2) 05 FILLER PIC X VALUE ')' 01 PATIENT-SSA 05 FILLER PIC X(19) VALUE 'PATIENT (PATNAME = ' 05 PATNAME PIC X(20) 05 FILLER PIC X VALUE ')' LINKAGE SECTION 01 PCS-MASK ------- ------- ------- PROCEDURE DIVISION CALL 'CBLTDLI' USING GU PCB-MASK PATIENT-SEGMENT HOSPITAL-SSA WARD-SSA PATIENT-SSA 1 8 9 10 17 18 19 20 39 40 ___________________________________________________________ HOSPITAL (HOSPNAME = RIVEREDGE ) WARD (WARDNO = 02) PATIENT (PATNAME = BROWN )
The above three SSA's work together in a call to retrieve patient whose name is BROWN from the ward no. 2 in hospital RIVEREDGE. This is a unique occurrence in HOSPITAL database.
In an SSA one can provide
- The name of the segment type
- A description of the condition in a qualification expression
- One or more command codes that extends the function
There are two types
- Unqualified SSA :- This only specifies the SEGMENT TYPE the program is interested in. Here you don't indicate a particular occurrence of a segment because you don't care which occurrence of a segment you get. The segment name is first eight characters padded by space upto the eighth position followed by a space in the ninth position instead of a left parenthesis. For example - HOSPITAL. This will retrieve the first occurrence of HOSPITAL segment.
- Qualified SSA: - This is addition to the SEGMENT TYPE, also contains one or more qualification statements. A qualified SSA describes the segment occurrence a program wants to access. This description is called a qualification statement having 3 parts. A qualified statement is enclosed in parenthesis. The part names the field that DL/I will use for segment search. The second part names the Relational Operator of two bytes telling DL/I what kind of comparison to make during the search. The third part is a variable length field that contains the values for comparison during DL/I search. Can code more than one qualification statement.
- Fully Qualified SSA: - The SSA's give complete information about each segment occurrence in the search hierarchy path.
- In the ninth position of SSA
- A BLANK indicates unqualified SSA
- A LEFT PARENTHESIS indicates qualified SSA
- An ASTERISK indicates one or more command codes
- Without SSA: - This is an unqualified call and DL/I assumes this to be an unqualified SSA also for the ROOT segment Level. The first occurrence of root segment is retrieved.
- With Unqualified SSA: - This is a qualified call and DL/I will locate the first occurrence of segment types specified in the call. For example
GU HOSPITAL WARD PATIENT
This will retrieve the first occurrence of PATIENT segment under the first occurrence of WARD segment under the first occurrence of HOSPITAL segment.
- With Assumed Unqualified SSA: - If any segment type is either not specified for any levels in the hierarchy path above the segment being retrieved (i.e. Missing Levels) or is specified without any Qualification Statement (i.e. Skipped Levels), DL/I will assume an Unqualified SSA for each missing or skipped segment types.
(MISSING LEVEL ) GU PATIENT (PATNAME =KRISH ) (SKIPPED LEVEL ) GU HOSPITAL WARD PATIENT (PATNAME =KRISH ) The effect of both the calls is same.
- With Fully Qualified SSA: - To fully qualify a call so as to retrieve a particular segment occurrence, you must specify a fully qualified SSA for that segment, and one for each level above it. The SSA's must be coded in the hierarchical sequence of segment types, starting with the root segment. You will however, retrieve only the segment identified in the last SSA in the Parameter list and the others above it are used only to further qualify the call, except in a special case involving SSA's using the D command code.
For example: GU HOSPITAL (HOSPNAME = MACNEAL ) WARD (WARDTYPE = INTENSIVE)
Any search field or the key field may be referenced in an SSA. The above example will retrieve the segment WARD whose ward type is INTENSIVE. One SSA is needed to retrieve the segment HOSPITAL, coded as GU HOSPITAL (HOSPNAME = MACNEAL )
- With Combinations of Qualified and Unqualified SSA's: - The way DL/I handles these calls depends upon the level at which the unqualified SSA's are coded.
GU HOSPITAL (HOSPNAME = RIVEREDGE ) WARD (WARDNO = 02 ) PATIENT
This will retrieve the first occurrence of the PATIENT segment in WARD No 02 of Hospital name RIVEREDGE
GU HOSPITAL WARD PATIENT (PATNAME = WHEELER)
Unqualified SSA's at higher levels such as HOSPITAL and WARD segment types and qualified SSA's at the lower levels at PATIENT segment type only tells where DL/I is to begin its search. DL/I does not limit its search to only those patient segment occurrences under the first occurrence HOSPITAL. Instead, DL/I searches all the way through the database until it reaches the occurrence of patient segment where the Patient is WHEELER. In this case the two unqualified SSA's tell DL/I to locate the second segment and start the search from there since we don't know in which Hospital and ward the patient WHEELER is admitted.
- Note Also specifying GU PATIENT (PATNAME = WHEELER ) wherein the segment types WARD & HOSPITAL are skipped in the call. DL/I will assume an unqualified SSA for the skipped segment types. The effect of the call is same as that of above example in which the levels are expressly unqualified in the call.
DATABASE DL/I CALLS
There are five types of database DL/I calls. They are
GET CALLS (GU, GN and GNP) GET HOLD CALLS (GHU, GHN and GHNP) INSERT CALL (ISRT) DELETE CALL (DLET) REPLACE CALL (REPL)
- = or EQ
- > = or GE
- Greater than or equal to
- < = or LE
- Less than or equal to
- > or GT
- Greater than
- < or LT
- Less than
- = or NE
- Not equal to
HOSPITAL DATABASE SEGMENT OCCURRENCE CHART
1 HOSPITAL MAC NEAL 2 WARD 01 / 018 / CARDIOVASC 3 PATIENT VEENA / 0003 / 082377 4 PATIENT SHEENA / 0008 / 071477 5 PATIENT MEENA / 0017 / 091377 6 WARD 04 / 017 / GASTRO 7 PATIENT HERO / 0004 / 051477 8 PATIENT ZERO / 0008 / 060277 9 WARD 08 / 000 / INTENSIVE 10 PATIENT WHEELER / 0001 / 081177 11 PATIENT PEELER / 0002 / 080477 12 PATIENT TRAILER / 0003 / 072877 13 PATIENT BOILER / 0004 / 071877 14 PATIENT JAILOR / 0005 / 080577 15 PATIENT SAILOR / 0006 / 080177 16 HOSPITAL RIVEREDGE 17 WARD 02 / 021 / PEDIATRIC 18 PATIENT MUNNU / 0003 / 061477 19 PATIENT CHUNNU / 0005 / 052277 20 WARD 04 / 008 / ORTHOPEDIC 21 PATIENT
RANDOM RETRIEVAL USING GU CALL
- This retrieves a unique segment occurrence randomly
- This is a fully qualified call wherein the program supplies a fully qualified SSA for each level in the hierarchy down to the segment being retrieved.
- GU call is also used to set up the Parentage at the retrieved segment occurrence for the subsequent GNP or GHNP calls issued in the program to retrieve its dependants sequentially.
GU HOSPITAL (HOSPNAME = RIVEREDGE ) WARD (WARDNO = 02 ) PATIENT (PATNAME = MUNNU )
This will uniquely retrieve the segment no. 18.
- Two status values are returned by DL/I in the status code field of PCB after executing the call using GU function
BALNK - indicates the retrieval was successful GE - indicates the segment occurrence was NOT FOUND
SEQUENTIAL RETRIEVAL USING GN CALL
- This retrieves a series of segments in Sequential order
- GN call is issued to retrieve the next segment occurrence from the current database position established by a GU or GN call. DL/I will start the search from current position forward to try to satisfy the call.
- Unqualified GN calls will traverse through the entire database
- One or more GN calls can be issued to retrieve the rest of the occurrences with the duplicate key.
- After each call examine the PCB mask fields for the status code, segment name and level number to determine the segment occurrence retrieved. Also it is difficult to figure out when you will go up in level, go down in level, or stay at the same level in database.
- DL/I Sequential Processing sequence within a database is always Top to Bottom, Left to Right and Front to Back along Twin occurrences.
1 Root Level HOSPITAL 15
2 16 Second Level WARD 13 WARD
3 14 17 Third Level PATIENT 9 PATIENT PATIENT
10 11 12 18 19 Fourth Level SYMPTOM TREATMNT DOCTOR SYMPTOM TREATMNT
4 5 7 22 SYMPTOM TREATMNT 6 DOCTOR 8 DOCTOR
- Reading sequentially through the database with an unqualified GN call, will retrieve different segment types at different levels First call retrieves a segment at the first or Root level (1) Second call retrieves a segment at the second level (2) Third call retrieves a segment at the third level (3) Fourth call retrieves a segment at the fourth level (4) Fifth, Sixth, Seventh, Eighth call retrieves segments at fourth level (5,6,7,8) Ninth call retrieves a segment at the third level (9) Tenth call retrieves a segment at the fourth level (10) Eleventh & Twelfth call retrieves segments at the fourth level (11, 12) Thirteenth call retrieves a segment at the second level (13), thereby moving from Level four to level two in one call.
- An important issue to be considered in sequential calls is the concept of position within the database.
GN calls without SSA's (unqualified GN calls)
- DL/I looks at the current position within the database and retrieves the next segment in hierarchical sequence
- Issuing a GN call without SSA as the first call in the program is equivalent to issuing a GN call without SSA. Since both retrieves the first segment in database, the first occurrence of root segment.
- Segments are retrieved all the way to the end of the database
Call 'CBLTDLI' using GN PCB-Mask I-O Area
GN call with Unqualified SSA's (Qualified GN call)
- GN calls with unqualified SSAs lets the sequential retrieval restricted to only a particular segment type, no matter what segments they are dependent upon.
For example: - GN PATIENT
When issued at the beginning of program execution, position would be established at the beginning of the database; and the call would retrieve the first patient segment 3. Next issue of the same call will retrieve the next patient occurrence in segment 9. Next issue of the same call will retrieve the next patient occurrence in segment 14. Next issue of the same call will retrieve the next patient occurrence in segment 17. Finally, the next issue of the same call would cause DL/I to return a GB status code since no more patients segments exist in the Hospital Database.
GN call with Qualified SSA's (Qualified GN Call)
- One strong reason to issue a qualified GN call instead of a GU call is to implement Skip-Sequential Processing
- In this, segments are always processed in their KEY SEQUENCE
- In Skip-Sequential Processing selected segments are processed in hierarchical sequence, with the restriction that the search values are presented to the program in Ascending sequence. If any search value that is lower than the value used in the previous call is provided, DL/I will return a GE status code, which is segment not exists. However, a GU call will go back to the beginning of database to find and retrieve the segment to the program whatever be the search values.
GN Calls - STATUS CODES
- When issued without SSA's (unqualified GN call) three values are returned
- GA - Moved up in level to retrieve the segment
- GK - New segment type at the same level is retrieved
- GB - End of database is reached
- When issued with Unqualified SSA's (Qualified GN call) one value is returned
- GB - End of database is reached
- When issued with qualified SSA's (Qualified GN call) two values are returned
- BLANK - Segment successfully retrieved
- GE - Segments not found following the current position
- The above status codes do not indicate error conditions
- Each GN call that retrieves a segment of the same type, or retrieves a segment lower in the hierarchy than the last one will return a BLANK status code.
- GA does not tell how many levels up, the position moved since the last call.
- One more GN call after returning a GB status code, DL/I will position itself at the beginning of the database.
SEQUENTIAL RETRIEVAL USING GNP CALL
- Performs sequential retrieval very similar to the GN function, except that it retrieves only segments that are subordinate to the currently established parent.
- Parentage must be established by issuing either a GU or GN call, in which case DL/I not only establishes a position on same segment occurrence, but it also, establishes parentage on that occurrence.
- The segment retrieved by the GN or GU call is treated as the parent segment for any subsequent GNP calls issued in the program.
- The GNP calls return only those segment occurrences that are
GNP calls without SSA's (Unqualified GNP call)
- Issuing a series of GNP calls without SSA's will retrieve only those segments that are dependant on the segment at which the parentage is established
GU HOSPITAL (HOSPNAME = Mac Neal)
Assume this establishes parentage; say at segment 1 in database.
- Next GNP call without SSA will retrieve the first word segment that is segment 2
- Further GNP calls without SSA will scan through the database and retrieve in hierarchical sequence all the segments that are dependent on Mac Neal Hospital Segment. The last one being segment 14
- One more GNP call after segment 14 would return a status code of GE indicating no more segments under the established parent. That is segment no.1
- The lower in level that parentage is established, the fewer segments an unqualified GNP call has access to.
GU HOSPITAL (HOSPNAME = Mac Neal ) WARD (WARDNO = 01 ) PATIENT (PATNAME = MUNNU )
Assume this establishes parentage; say at segment 3 in database, the patient segment for patient Munnu.
- Next GNP calls without SSAs would only have access to segments 4, 5, 6, 7, and 8 in the database
- One more GNP call after segment 8 would return a status code of GE indicating no more segments dependant on segment 3. That is the patient name MUNNU.
GNP call with Unqualified SSA's (Qualified GNP call)
- GNP calls with unqualified SSA's will sequentially retrieve only segment of the particular segment type.
GU HOSPITAL (HOSPNAME = Mac Neal)
Assume, this established parentage, say at segment 1 in database.
In this case, GNP calls that specify an unqualified SSA for the Patient segment retrieves the segments 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 and 14 in the first database record that is segment no. 1 for Mac Neal Hospital
However, if an unqualified GNP calls are issued with segment no. 1 as the established parent, even ward segments no. 2 and 13 would be retrieved as well in the sequence along with the above segments.
- Results could be dramatically wrong if a mistake is made in establishing parentage before issuing GNP calls.– While coding a qualified GNP call do not include SSA's for segments at a level higher than or equal to that of the currently established parent segment. If you do, DL/I will return a GP status code.
GNP call with Qualified SSA's (Qualified GNP call)
- GNP calls with qualified SSA's can be used when performing Skip-Sequential Processing.
- Perform a series of GNP calls using SSA only for the segment type being retrieved.
GU HOSPITAL (HOSPNAME = Mac Neal ) WARD (WARDNO = 01 )
Assume, this established parentage at ward no 01 in Mac Neal Hospital, say at segment 2 in the database.
GNP PATIENT (BEDIDENT = Supplied Value)
Now, issuing GNP calls with a single qualified SSA for the patient segment instead of GN calls, the program has automatically limited the area of search to only there segments which are dependant on ward no. 1. That is segment 2.
If GNP calls are replaced y GN calls with the single SSA, this would read through all the patient segments in the database, rather than stopping at the end of Ward No. 1 segment.
GNP Calls - STATUS CODE
- When issued without SSA's (unqualified GNP call)
- GA - Moved up in level to retrieve the segment
- GK - New segment type at the same level is retrieved
- GE - End of database is reached
- When issued with unqualified SSA's (qualified GNP call)
- GE - End of database is reached
- When issued with qualified SSA's (Qualified GNP call)
- BLANK - Segment successfully retrieved
- GE - Segments not found following the current position
- A GP error code is returned by DL/I, which almost always represent a Programming ERROR as below :-
- If a GNP call is issued without first establishing parentage on a segment by a GU or GN call.
- If the GU or GN call is issued to establish the parentage is not executed successfully before the GNP call was issued.
- An established parent segment is deleted before the GNP call depending on that parent is issued.
- If the SSA's coded in the GNP call contains errors
UPDATING AND DELETING SEGMENTS
- Updating and Deleting segments always requires the program to perform a sequence of two calls.
- The first call being a GET HOLD function to retrieve the segment that the program intends to Update or Delete
- The second call being a REPL or DLET function to perform the replacement or deletion of the segment eventually.
- Any intervening calls between the first and the second call will nullify the effect of the GET HOLD call. The practical implication of this is that the program can proceed with the other processing if it is decided not to go ahead with the replacement or the deletion of the segment. Hence any explicit action to cancel the effect of a get hold call is not required in the program.
GET HOLD CALLS
- Are GHU, GHN, GHNP
- Perform similar functions of GU, GN and GNP apart from certain additional functions such as
- DL/I saves information about the segments location
- DL/I writes information in system log data sets, which are used to restore a database should recovery is ever necessary.
- Same kind of SSA's used with normal calls can be used with Get Hold calls to bring a particular segment into the I-O area
- Status codes returned by DL/I are also identical, given the similar circumstances
DELETE AND REPLACE RULES
Rule No.1 - Must issue a Get-Hold call prior to issuing a REPL or DLET function call
Rule No.2 - Should not issue any other call using the same PCB, between the time a Get Hold call is issued and the time a Replace or Delete call is issued, unless that other call is also a Get Hold call.
Rule No.3 - Should not normally code SSA's in the Replace or Delete calls except when the Get Hold call is with one or more SSA's using the D command code.
Rule No.4 - The KEY field in the segment cannot be modified before the REPL or DLET calls.
REPLACING SEGMENTS IN THE DATABASE USING THE REPL FORM
- Must issue a Get Hold call to retrieve the segment data into I-O area.
- Changes can be made to the data in I-O area except the KEY field.
- Issuing a REPL call will cause changes to the segment to be rewritten to the database.
- If the Get Hold call is a Path call issued with one or more SSA's using the D command code, a REPL call can be issued with SSA's
- The SSA's can be Qualified or Unqualified
- The SSA's must use N command code for those segments whose data you DON'T want to be rewritten to the data.
- If the REPL call is issued without SSA's, it operates all the segments retrieved along the path and all the segments in the path will be rewritten to the database.
CALL 'CBLTDLI' USING GHU PCS-MASK PATIENT I-O AREA HOSPITAL-SSA WARD-SSA PATIENT-SSA
Make appropriate changes to Patient segment data.
CALL 'CBLTDLI' USING REPL PCB-MASK PATIENT I-O AREA
REPL CALL - STATUS CODE
DJ - Replace call issued without an immediately preceding GETHOLD call. DA - Program has changed the segment's key field RX - Encountered a Replace Rule Violation AJ - Used an SSA without command code in the REPL call
DELETING SEGMENTS IN THE DATABASE USING THE DLET FUNCTION
- Must issue a Get Hold call to retrieve the segment data into the I-O area
- Issuing a DLET call will cause the segment to be deleted, and automatically deletes all its subordinate occurrences from the database
- If the Get Hold call is a path call issued with one or more SSA's using the D command code, a DLET call be issued with SSA
- SSA can only be unqualified (i.e. no command codes)
- A DLET call using an Unqualified SSA without a command code will cause the segment named by the SSA to be deleted along with all its dependants. However, segments above it will not be deleted.
- A DLET call without SSA following a Get Hold path call operates on the entire path deleting all the segments in the path being retrieved.
- A DLET call without SSA following a normal Get Hold call will only delete the segment specified in the last SSA of Get Hold
CALL 'CBLTDLI' USING GHU PCB-MASK PATIENT I-O AREA HOSPITAL-SSA WARD-SSA PATIENT-SSA
DLET CALL - STATUS CODES
DJ - Delete call issued without an immediately preceding Get Hold call DA - Program has changed the segment's KEY FIELD DX - Encountered a Delete Rule Violation AJ - Used an SSA which is Qualified
INSERTING SEGMENTS INTO AN EXISTING DATABASE
- ISRT call is issued to insert a new segment into the database. Insertion of segments can be made in any sequence.
- Program should build the segment occurrence data in the segment description area in Working-Storage section before issuing a call.
- PCB for the database in the PSB should specifying as processing options I or IS in the PROCOPT operand for permitting insertions of segments in the Ascending Sequence in the Insert Mode. (A or AS is also permitted)
- If the ISRT call is issued with an unqualified SSA, DL/I will try to insert the segment based on the current position in the database. The current position is established by a previous retrieval call, followed by an Insert call using the unqualified SSA for the segment to be inserted.
GU HOSPITAL (HOSPNAME = Mac Neal) WARD (WARDNO = 01 ) ISRT PATIENT
- If the ISRT call is issued with a qualified SSA, describing the path along with the insertion is to be made, with an unqualified SSA for the segment being inserted with an
ISRT HOSPITAL (HOSPNAME = Mac Neal ) WARD (WARDNO = 01 ) PATIENT
- If the inserted segment occurrence has a unique key field DL/I uses the key of the new segment to determine where
DBD INSERT RULES
- When DBA defines a segment type that does not have a key field, or has a non-unique key field, it is necessary to tell DL/I where to insert the new segment occurrences for that segment type in the twin chain.
- The RULES operand of the SEGM statement of DBD tells DL/I how to handle segment insertions in such situations.
- RULES operand has three options that tells DL/I where in the twin chain to insert the new segment which does not have a unique key field. They are as follows
- FIRST - Says that the new segment will always be inserted at the beginning of the twin chain.
- LAST - Says that the new segments will always be inserted at the end of the twin chain. This is the default.
- HERE - Says that the new segment will be inserted after the segment at which the program within the twin chain establishes the current position before the ISRT call is issued. If the current position is not established before inserting the new segment, with this rule, a new segment occurrence is always inserted at the beginning of the twin chain if no position is established within the twin chain.
- DL/I uses the key field to find the approximate position within the twin chain to insert an segment that has non-unique key field. The insert rule is then applied to determine where to insert the new segment occurrence relative to all the segments having the same non-unique key value. First, tells DL/I to insert the new segment at the beginning of all those segments having the same non-unique key value. Last, tells DL/I to insert the new segment after all those segments having the same non-unique key value. Here, tells DL/I to insert the new segment within the twin chain after establishing the current position within it. If the appropriate key value position is not established, DL/I will insert the new segment at the beginning of the set of segments having the same key value.
ISRT CALL (INSERT MODE) - STATUS CODE
II - The segment already exists in the database. A duplicate key value is being inserted into.
IX - Encountered an Insert Rule Violation. Program tried to insert a segment into the wrong place in the database. For example: A patient segment is being inserted under the Facility segment, when it is in fact dependent upon the Ward segment.
LOADING SEGMENTS INTO AN EMPTY OR SCRATCH DATABASE
- ISRT call is also issued to load a database with segments from the scratch
- PCB for the database in the PSB should specify as processing options L or LS in the PROCOPT operand for permitting loading of segments in the Ascending sequence in the Load mode
- Insert commands in Load Programs normally load segments in Ascending sequence only with certain exceptions.
- One important rule for ISRT call is that the segment being loaded or inserted must be identified in an single unqualified SSA, since qualified SSA is not valid.
- Programs designed to Load databases normally use ISRT calls with Unqualified SSA
- Segments must be presented to the Load Program in the Hierarchical Sequence. It means that root segments must be presented to the load program in root key sequence and all dependant segments must be presented in hierarchical sequence following each root key.
- The appropriate segment name for the segment type being loaded is moved into the Unqualified SSA are before
- DL/I gets the Qualification information for the segment being inserted from I-O area
- It is however valid to include Qualified SSA's to completely describe the path with a restriction that the SSA for the segment being loaded cannot be qualified. Also, you cannot include SSA's at levels lower than the level at which the segment is being loaded.
CALL 'CBLTDLI' USING ISRT PCB-MASK I-O AREA UNQUALIFIED-SSA
ISRT CALL (LOAD MODE) - STATUS CODES
- LB - When you try to load the same segment twice i.e. segment already exists
- LC - The segments being loaded are not in their Hierarchical sequence i.e. key values out of sequence
- LD - No parent for the segments being loaded. You cannot load a dependant segment until its parent has been loaded.
- LE - Segment types out of sequence. For example: - If you tried to load a facility segment before a patient segment.
ADVANCED DATABASE PROCESSING
BOOLEAN SSA STATEMENTS
- Sometimes an SSA needs more than one qualification statement when there are more than one condition to be tested to qualify at that segment.
- The conditions are tested on more than one field in a segment Boolean Operators are needed to connect these qualification statements.
- The valid Boolean Operators are
* (Asterisk) or the & (Ampersand) -------> Logical AND + (Plus) or the | (Vertical Bar) ---------> Logical OR
- DL/I can evaluate any complex group of qualification statements. A group of qualification statements connected by AND operators is called a SET of qualification statements.
- In order for the entire expression to be satisfied, any one set of qualification statements needs to be satisfied.
- In order for the set to be satisfied, all the qualification statements within that set must be satisfied.
- If AND and OR operators are used in a single SSA, group all the statements connected by the AND operators as a SET.
- First AND is evaluated, then OR as per normal Logic Rules.
- For example
GU Segment ( A = 1 * B = 2 + C =3 * D = 4 ) A = 1 AND B = 2 OR C = 3 AND D = 4
Qualification Qualification Qualification Qualification Statement AND Statement Statement AND Statement
Set of qualification statements Set of qualification statements OR
SSA'S USING COMMAND CODES
- Command codes in a SSA makes the call powerful since DL/I treats such SSA'S differently from those without the command codes while performing some special functions.
- Command codes save programming and processing time
- Command codes are specified in an SSA following the segment name and an Asterisk '*'
- An Asterisk '*' in the ninth position in a SSA indicates that one or more command codes follow the asterisk
- A Blank or Left Parenthesis marks the end of command codes
- ONE or MORE command codes can be used in any combination
- Ten command codes are available under IMS
- F - Locate First Occurrence
- L - Locate Last Occurrence
- D - Retrieve this segment data into the I-O Area (Path Call)
- N - Do not replace this segment
- C - Concatenated key in this SSA
- Q - Enqueue this segment
- U - Maintain current position at this level
- V - Maintain current position at this and higher level
- P - Establish Parentage at this level
- - - Null command code
- Command codes in a Qualified SSA
- WARD *D(WARDNO =03)
- WARD *DNP(WARDNO =03)
- Command codes in an Unqualified SSA
- WARD *PD
F COMMAND CODE
- Tells DL/I to begin the search with the first occurrence of this segment type in a twin chain under its parent.
- It can be used only with GN, GNP, GHN and GHNP calls
- In a retrieved call this command code allows the segment occurrence to be inserted as first occurrence in the segment type which has non-unique or no key field and RULES=HERE is specified for this segment in the DBD.
- Suppose you search through all the treatment segments under a particular patient segment occurrence for a treatment type of Morphine. If you find one, you would like to print all the Treatment occurrences for that patient.
WITHOUT COMMAND CODE
1. GU HOSPITAL (HOSPNAME = RIVEREDGE ) WARD (WARDNO = 04 ) PATIENT (BEDIDENT = 08 ) 2. GNP TREATMNT (TRTYPE = MORPHINE ) 3. If status code is GE, exit from procedure, Else if Blank 4. GU HOSPITAL (HOSPNAME = RIVEREDGE ) WARD (WARDNO = 04 ) PATIENT (BEDIDENT = 08 ) 5. GNP TREATMNT 6. Print a treatment segment occurrence 7. Loop back to step 5 until a GE status code
WITH COMMAND CODE
1. GU HOSPITAL (HOSPNAME = RIVEREDGE ) WARD (WARDNO = 04 ) PATIENT (BEDIDENT = 08 ) 2. GNP TREATMNT (TRTYPE = MORPHINE ) 3. If status code is GE, exit from procedure, Else if Blank 4. GNP TREATMNT * F 5. Print a treatment segment occurrence 6. GNP TREATMNT 7. Loop back to step 5 until status-code GE
L COMAMND CODE
- Tells DL/I to retrieve the last occurrence of this segment type in a twin chain under its parent
- In an insert call this command code insert the segment occurrence as the last occurrence in the segment type which has non-unique or no key field.
- L command code can be used only in the dependent segment types. It is ignored, if used in the root segment.
- Suppose you want to retrieve the last twin occurrence of the Treatment Segment type for a particular patient segment.
WITHOUT COMMAND CODE
1. GU HOSPITAL (HOSPNAME = Mac Neal ) WARD (WARDNO = 08 ) PATIENT (BEDIDENT = 04 ) 2. GNP TREATMENT 3. Loop back to step 2 until status code is GE. When GE, the I-O area will contain the last twin occurrence of treatment.
WITH COMMAND CODE
1. GU HOSPITAL (HOSPNAME = Mac Neal ) WARD (WARDNO = 08 ) PATIENT (BEDIDENT = 04 ) TREATMNT * L
D COMMAND CODE & N COMMAND CODE
- D & N command codes work together to process multiple segments in a single call.
- D command code performs a PATH call, wherein, DL/I retrieves multiple segments along the retrieval path in the I-O area. Thus the I-O area must be defined large enough to accommodate all the segments being retrieved in the path. DL/I will place the segment at the higher level in front of the segment at the lower levels. The segment layouts within the I-O area must be defined in the hierarchical structure.
- If D command code is not coded, only the segment identified by the last SSA is placed in the I-O area by default. Necessary to retrieve all the segments in the hierarchical path. Therefore, you can code D command code in the higher level SSA's only for those segments you want DL/I to place in the I-O area.
- A processing option of P must be coded in the PROCOPT operand of the PCB in your PSB for the segment, if D command code is to be used in an SSA for that segment. PROCOPT = P
- DL/I remembers how many segments are stored in the I-O area by the Get Hold path call. So a subsequent replace call without SSA's will replace all the segments in the I-O area along the path.
- N command code is coded in the SSA'S for those segments used in the Replace call that you don't want to Replace.
- SSA'S with the N command code is an exception to the rule that qualified SSA'S cannot be coded in a Replace call.
- One can code a combination of D and N command codes within the same SSA if the same sets of SSA'S are used in both the Get Hold Path Call and the Replace Call.
WITH D COMMAND CODE
GHU HOSPITAL * D (HOSPNAME = RIVEREDGE ) WARD * D (WARDNO = 02 ) PATIENT (BEDIDENT = 0005 )
WITH N COMMAND CODE
REPL HOSPITAL * N (HOSPNAME = RIVEREDGE ) WARD * N (WARDNO = 02 ) PATIENT (BEDIDENT = 0005 )
WITH D & N COMBINATION
Both for GHU & REPL HOSPITAL * DN (HOSPNAME = RIVEREDGE ) WARD * DN (WARDNO = 02 ) PATIENT (BEDIDENT = 0005 )
- D command code in one or more higher level SSA'S will also place the additional segment in lt I-O area. It is not if SSA omitted default n replace all implicit N will be ignored for Get and D W.
RETRIEVING AND REPLACING WITHOUT COMMAND CODE
1. GU HOSPITAL (HOSPNAME = RIVEREDGE ) 2. Save Hospital information 3. GN WARD (WARDNO = 02 ) 4. Save Ward information 5. GHN PATIENT (BEDIDENT = 0005 ) 6. Print Patient, Ward and Hospital information 7. Update information in the Patient segment 8. REPL
C COMMAND CODE
- C command code is used in situations where you would normally use fully qualified calls.
- It allows you to use a concatenated key value in a single SSA rather than using a set of fully qualified SSA'S
- The concatenated key must be enclosed in Parenthesis and no key in the path can be omitted from the concatenated key.
- Only a single SSA naming the segment to be retrieved can be used in the call with C command code.
WITHOUT C COMMAND CODE
GU HOSPITAL (HOSPNAME = RIVEREDGE ) WARD (WARDNO = 02 ) PATIENT (BEDIDENT = 0003 ) DOCTOR (DOCTNAME = KILLER )
WITH C COMMAND CODE
GU DOCTOR * C (RIVEREDGE 02 0003 KILLER ) CALL 'CBLTDLI' GU CONCATENATED-KEY 01 CONCATENATED-KEY 05 SEG-NAME PIC X (08) 05 CON-CODE VALUE 'X C '(' 05 HOSP-KEY X (02) 05 WARDKEY PIC 05 CLOSE X (01) VALUE ')'
Q COMMAND CODE
- Q command code is only used when multiple applications will be accessing the same database at the same time. Normally used in the O/L MPP where the O/L programs are running under multitasking environment and more than one task can update the same database at the same time.
- If you do not want this to happen, issue DL/I calls with Q command code to ENQUEUE the particular segment occurrence for exclusive use by your task, preventing other online transactions from updating the segment until your task is completed.
- Other users cannot make a Get Hold type call for that segment, only get calls can access that segment. Get Hold type calls must wait until the Enqueued segment has been Dequeued through the DEQ call, CHKP call, or the program termination.
- Q command code set at the root segment level will not allow any other user to gain access to any segment in that database record.
- A one-byte class identifier in the range of 'A 'through' J follows Q command code. This class identifier must be specified in the DEQ call to dequeue the segments.
GHU HOSPITAL WQB ( HOSP = APPDO ) WARD (WARDNO = 05) PATIENT (= MUNNU)
U AND V COMMAND CODES
- U and V command codes are used to prevent a GN or GNP call from leaving the current position.
- They help exercise some control over calls that cannot be satisfied for a particular parent, but can be satisfied further in the database under a different parent.
WITHOUT U COMMAND CODE
1. GU (HOSPITAL ( HOSPNAME = Mac Neal ) 2. GNP WARD 3. GET A WARD KEY FROM PCB AND STORE IN WARD SSA 4. GNP WARD (WARDNO = WORDKEY) PATIENT 5. LOOP BACK TO STEP 4 UNTIL A GE STATUS CODE
In the above example you have to get the key value of the ward segment out of the PCB every time Step 2 of the procedure is executed. Store the key value into the qualified SSA in Step 4 before starting the loop that retrieves the Patient segments. This keeps the GNP calls within the same domain in the database. GE status code is returned by DL/I after you run out of Patient segments for each Ward, just as though you had established parentage at the Ward Level for getting the necessary Control Breaks.
WITH U COMMAND CODE
1. GU HOSPITAL (HOSPNAME = Mac Neal ) 2. GNP WARD 3. GNP WARD * U PATIENT 4. LOOP BACK TO STEP 3 UNTIL A GE STATUS CODE
In the above example coding a U command code in an unqualified SSA has the same effect as using a qualified SSA at that level. Using U command code at the ward level tells DL/I to maintain the current position established on the ward segment level.
WITH V COMMAND CODE
GNP WARD * U PATIENT * U SYMPTOM (OR) GNP PATIENT * V SYMPTOM
In the above example, V command code causes DL/I to act as though U command code were set at that level, and at all the levels above it. The two sets of SSA'S are functionally the same. The command saves the trouble of coding U command codes in SSA'S at each higher level.
P COMMAND CODE
- P command code allows the parentage to be set at any levels in the database other than the one identified by the last SSA
- Code the P command code in the SSA for the segment at which you would like the parentage established and DL/I will still retrieve the segment identified by the last SSA, but sets parentage where you set the P command code.
- The parentage will be destroyed when another GU or GN call is executed.
WITH P COMMAND CODE
1. GU HOSPITAL (HOSPNAME = Mac Neal ) WARD (WARDNO = 08 ) 2. GNP PATIENT 3. PRINT A PATIENT SEGMENT 4. LOOP BACK TO STEP 2 UNTIL A GE STATUS CODE
WITH P COMMAND CODE
1. GU HOSPITAL (HOSPNAME = Mac Neal ) WARD * P (WARDNO = 08 ) PATIENT 2. PRINT A PATIENT SEGMENT 3. GNP PATIENT 4. LOOP BACK TO STEP 2 UNTIL A GE STATUS CODE
By using a P command code, you saved one call by retrieving the first patient segment in the Get Unique call itself and setting the parentage at the ward level.
NULL COMMAND CODE
- The NULL command code '___ ' is used in the SSA to simplify the construction of SSA within the program and does not perform any function at all.
- The SSA is treated as if no command code were coded.
- The null command code '__' reserves one or more positions in a SSA into which you can store command codes during the program execution. This way making it possible to use the same set of SSA'S for more than one purpose.
- HOSPITAL *------- (HOSPAME = Mac Neal )
MULTIPLE POSITIONING WITHIN THE PCB
- With Multiple Positioning DL/I maintains a unique position within a Database Record for each dependent segment type at each level in each Hierarchical path in the database.
- Multiple Positioning is normally used to access segments of two or more types dependent on a specific parent.
- The segments are processed sequentially at the same time, enabling parallel processing within the database.
- Multiple Positioning lets a program maintain more than one position within a database using a single PCB.
- Multiple Positioning for a database is specified in the PCB statement in the PSB for POS operand. For example
PCB TYPE=DB, NAME=HOSPITAL, POS=M or S M stands for Multiple, S stands for Single Positioning If POS operand is not coded, the default is single positioning
- It is important for a programmer to know what is in effect for your PCB before coding the program. Since it is dangerous to change the parameter from M to S in the POS operand for the PCB
WARD 2 FACILITY 20
SYMPTOM 14 TREATMNT 16 DOCTOR 18
15 17 19
SYMPTOM 4 TREATMNT 7 DOCTOR 10
5 8 11
6 9 12
- In the above Hierarchy assume that there is a one to one relationship between SYMPTOM, TREATMNT and DOCTOR segments. For each SYMPTOM segment there must be a corresponding TREATMNT and DOCTOR segments. This type of relationship between the segment types in the database illustrates the need for Multiple Positioning for some types of Sequential Retrievals
- Suppose we want to print for a PATIENT segment each set of SYMPTOM, TREATMENT and DOCTOR segments under that PATIENT and we don’t care about the sequence of the segments.
GU HOSPITAL (HOSPNAME = RIVEREDGE) WARD (WARDNO = 02 ) PATIENT (BEDIDENT = 1012 )
With the above sequence of calls we will first retrieve all the SYMPTOM segments, followed by all the TREATMNT segments, followed by all the DOCTOR segments. However, this is not what we want because what we really like to do in this case is to first retrieve the SYMPTOM segment, followed by a TREATMNT segment, followed by a DOCTOR segment.
Suppose we code as follows
GU HOSPITAL (HOSPNAME = RIVEREDGE) WARD (WARDNO = 02 ) PATIENT (BEDIDENT = 1012 ) GNP SYMPTOM GNP TREATMNT GNP DOCTOR
This will work only for the first execution of above call sequence retrieving segments 4, 7 and 10. But the second execution will return a GE status code indicating there are no more SYMPTOM segments under that Parent i.e. PATIENT whose BEDIDENT = 1012. To get the next SYMPTOM segment, DL/I will have to remember the position of the last SYMPTOM segment retrieved, as well as the positions of the last TREATMNT and DOCTOR segments.
Suppose we code
GU HOSPITAL (HOSPNAME = RIVEREDGE) WARD (WARDNO = 02 ) PATIENT (BEDIDENT = 1012 ) GN SYMPTOM GN TREATMNT GN DOCTOR
This time the sequence of segments retrieved will be 4, 7, 10, 14, 16, 18 followed by a GE status code. This call sequence will go through the entire database retrieving only the first occurrence of the SYMPTOM, TREATMNT and DOCTOR segment under each PATIENT segment.
Now, retrieving with Multiple Positioning, DL/I maintains a separate Unique position within the Database Record for each Dependent Segment Types at each level in each Hierarchical Path. A chart below illustrates this
A WARD B FACILITY
D SYMPTOM E TREATMNT F DOCTOR
Figure 7 - Note That you cannot maintain two positions on the same segment type. Also, the separate positions are maintained only on the segments dependent upon a particular parent.
Suppose we code as follows
GU HOSPITAL (HOSPNAME = RIVEREDGE) WARD (WARDNO = 02 ) PATIENT (BEDIDENT = 1012 ) GNP SYMPTOM GNP TREATMNT GNP DOCTOR
Assuming that Multiple Positioning is in effect, the first time we retrieve segments 4, 7 and 10. The second time we retrieve segments 5, 8 and 11 using GNP calls. The third time we retrieve segments 6, 9 and 12 using GNP calls.
This is possible because DL/I maintains a different position for each segments at D, E and F in the hierarchy chart above.
MULTIPLE PCB's IN A PSB
- When a program needs access to more than one database, it has a PCB for each.
- A single PCB can refer to only one DBD
- Multiple PCB's can also be defined for a single database in which case the program has two or more views of the same database and DL/I will maintain a unique position in that database for each PCB you define on it.
- Multiple PCB's on the same database is defined when the program require access to two completely different logical data structures, each describing different segments in different hierarchical paths from the same database.
- Each PCB in SPB has its own PCB mask in the Linkage Section and is specified in the ENTRY statement for addressing that block in the order in which PCB's appear in the PSB.
- Multiple Positioning enables processing within one portion of a Database record parallely wherein, the program processes different segment types in parallel as long as those segment types are dependant upon the SAME parent whereas, Multiple PCB's allow the program to process the segments in parallel, no matter where in the database the segments are
- A good example of where parallel processing using Multiple PCB will be in Transferring a Patient from one hospital ward to another hospital ward. To do that you first retrieve a patient segment from one part of database and insert it in another part of the database. You will then sequentially process that transferred patient's SYMPTOM the new place of the PATIENT segment.
- With a single PCB, as soon as you insert the PATIENT segment under a new WARD segment occurrence, you lose position on the old PATIENT segment and finding its dependents will be difficult without retrieving the old PATIENT segment again. Also each time your insert one of the dependants under the new parent you lose position again.
- Suppose you define two PCB's and both of them describe the same Logical Data Structure. You need two PCB's so that you can maintain two positions in different parts of the database simultaneously.
Suppose we code as follows
Call 'CBLTDLI' using GU PCB1-MASK I-O AREA OLD HOSPSSA OLD WARDSSA OLD PATIENTSSA
Call 'CBLTDLI' using ISRT PCB2-MASK I-O AREA NEW HOSPSSA NEW WARDSSA PATIENTSSA-UNQUALIFIED
Call 'CBLTDLI' using GNP PCB1-MASK I-O AREA
Move PCB1-Segment Type to New-Unqualified-SSA
Call 'CBLTDLI' using ISRT PCB2-MASK I-O AREA New-Unqualified-SSA
- A logical database is normally used to combine segments from more than one Physical Database into a NEW hierarchy structure using the logical relationships
- A Physical Database is used to describe the physical structure of a database and the hierarchical relationships between the segment types.
- Logical Relationships allow the DBA to define new hierarchical relationships without actually having to create a new physical database.
- DBDGEN process can also be used to define Logical Database.
- It is a path between segments that otherwise would be unrelated. This relationship is always between two segments
- The two segments may reside in separate physical databases, though they can also be within the same database physical.
- The basis of a logical relationship is a segment called the Logical Child segment. The Logical Child is a physical database segment having two parents: its Physical parent segment and its logical parent segment.
- Logical twins are occurrences of a logical child segment type that are all subordinates to a single occurrence of the logical parent segment type.
SYMPTOM TREATMNT DOCTOR PBILL BILLING HISTORY
PHYSICAL HOSPITAL DATABASE PHYSICAL HISTORY DATABASE
Figure 9 :- A NEW LOGICAL DATA STRUCTURE
- Note A new segment type called the PBILL segment is created. Each occurrence of it points to the appropriate occurrence of the BILLING segment in the HISTORY database.– A new logical DBD, which maps against two physical DBD'S defining the logical structure above, is coded.– PSB'S requiring access to the logical structure above would now reference the logical DBD rather than either one of the Physical DBD'S– In Logical Relationships Terminology– PBILL segment in the HOSPITAL physical database is called a LOGICAL child segment.– PATIENT segment for PBILL segment is Physical Parent Segment BILLING segment in the HISTORY physical database to which PBILL segment is pointing to is called a Logical Parent Segment.– This is a Unidirectional Logical Relationship and the advantage is that the BILLING information exists in only one place in the HISTORY physical database.– PBILL and BILLING segments are logically relatedWhen a logical child is accessed through its Physical Access path, the destination parent is its Logical parent. But when it is accessed through its Logical access path, the destination parent
DBDGEN'S FOR PHYSICAL DATABASE WITH LOGICAL RELATIONSHIPS
- A logical relationship is implemented by specifying them in the DBDGEN for the physical database involved.
In the DBD for Hospital Database
SEGM NAME=PBILL PARENT=((PATIENT, DBLE), (BILLING, HISTDBF))
In the DBD for HISTORY Database
SEGM NAME=BILLING, PARENT=NAME LCHILD NAME=(PBILL, HOSPDBF)
In the DBD for Logical Database
DBD NAME=HOSPITAL, ACCESS=LOGICAL DATASET LOGICAL SEGM NAME=HOSPITAL, PARENT=0, SOURCE=((HOSPITAL, DATA, HOSPDBD)) SEGM NAME=WARD, PARENT=HOSPITAL SOURCE=((WARD, DATA, HOSPDBF)) SEGM NAME=PATIENT, PARENT=WARD, SOURCE=((PATIENT, DATA, HOSPDBD)) SEGM NAME=PBILL, PARENT=PATIENT SOURCE=((BILLING, DATA, HISTDBF)) DBDGEN FINISH END
PSBGEN USING LOGICAL DATABASE
- There is no difference in setting up the PCB in the PSB for the logical database and physical database.
PCB TYPE=DB, DBDNAME=HOSPHIST, PROCOPT=A, KEYLEN= SENSEG NAME=HOSPITAL, PARENT=0 SENSEG NAME=WARD, PARENT=HOSPITAL SENSEG NAME=PATIENT, PARENT=WARD SENSEG NAME=PBILL, PARENT=PATIENT PSBGEN LANG=COBOL, PSBNAME=LOGICPSB END
IMS SYSTEM DATASETS
IMSVS.RESLIB This dataset contains all the IMS load modules that make up the IMS software DB as well as DC. Specified in STEPLIB or JOBLIB
IMSVS.PGMLIB This dataset contains all the IMS application program load modules. Specified in STEPLIB or JOBLIB
IMSVS.PSBLIB This dataset contains all the generated PSB'S used by the application program during execution. Specified in IMS Ddname.
IMSVS.DBDLIB This dataset contains all the generated DBD'S used by the application program during execution. Specified in IMS Ddname.
IMSVS.MACLIB This dataset contains the definitions of the Macros that are used to generate the PSBGEN and DBDGEN macros.
IMSVS.PROCLIB This dataset contains the IMS catalogued procedures supplied with IMS
IMSVS.ACBLIB This dataset is used to store the combined PSB'S and DBD'S information before an application program is executed. An application program execution JCL must have access to the IMSVS.RESLIB and IMSVS.DBDLIB datasets.
When a program is executed, IMS must combine the information in your DBD and PSB before the execution could begin. To save IMS this trouble each time the program executes, the DBA may choose to merge the DBD and PSB information ahead of time. To do this, a procedure called ACBGEN, which stands for Application Control Block Generation is executed. Once generated, the execution JCL must reference IMSVS.ACBLIB rather than the PSBLIB and DBDLIB. The use of this dataset is optional for Batch DL/I programs, but is required for MPP and BMP programs.
APPENDIX - A
Processing Options - PROCOPT
- Get functions GU, GN, GNP, GHU, GHN, GHNP
- Insert function ISRT
- Replace function REPL. Also implies G.
- Deletes function DLET. Also implies G
- All includes above four functions G, I, R, D
- Required for Path calls if D command code is to be used in the SSA for the segment.
- Get calls only, and no Get Hold calls are allowed. If you specify GO or GOP, then only Get calls like GU, GN, GNP are allowed. If specified for all the PCB'S in the PSB, then you can execute a DL/I Batch program without making the on-line Databases off-line.
- Enqueue the segment or database for on-line program. This facility allows MPP programs to exclusively use this resource in a Multitasking environment.
- Load function for database initial loading
- Get segments in Ascending Sequence only (HSAM)
- Load segments in Ascending Sequence only.
- Parameter by Default is a (All)
- The segment is key sensitive only, cannot access data.
APPENDIX - B
DL/I STATUS CODES
- The call did not specify a segment I-O area (All)
- SSA with a hierarchical error. (Get & ISRT)
- Call requires atleast one SSA (ISRT)
- Error encountered when trying to open the database dataset. An error in the JCL DD Statement. (All).
- The call specifies an Invalid SSA
- The field named in a qualified SSA is not correct (All get calls and ISRT)
- Call attempted an unauthorized operation not allowed by the processing options or Sensitive segments specified in the PCB (all calls)
- Call caused an operation resulting in a physical I-O error (All calls)
- The I-O area specified in the call is too large, but the program's PSB may be incorrect. (DLET, REPL and ISRT calls)
- The sequence field with key (non-replaceable field) has been changed in the program's I-O area. (DLET, REPL calls)
- No preceding Get Hold call for a Delete or Replace operation (DLET, REPL calls)
APPENDIX - C
SYSTEM SERVICE - DL/I CALLS
- There are eight DL/I calls using which IMS performs various system services functions.
- Four important calls are listed below
- A point in the execution of program when, the changes made to the database are considered complete and accurate.
- Once checkpointed, the changes made are not reversible.
- By default, the Beginning as well as the normal end of a Batch program are checkpoints. However, intermediate checkpoints can be established while a program is executing by issuing a CHKP call.
- CHKP call causes all the databases changes made since the last checkpoint to be permanently committed to the physical database thereby making a Backout impossible.
- Checkpoint is also known by other similar terms such as synchronization point, commit point, sync point, integrity point
- A CHKP call causes the database position for a PCB to be reset, apart from releasing all the locks held by program.
- A CHKP call is of two types. They are
BASIC CHECKPOINT CALL
- Can be issued by a BATCH and BMP programs
- MPP and Message Driven Fast Path programs must issue only this call
- Apart from committing changes made to the data, it also establishes position in the program from where to Restart, in case the program abnormally terminates
CALL 'CBLTDLI' USING CHKP I-O PCB MASK CHECKPOINT-ID
The I-O PCB must be the first PCB listed on the ENTRY statement normally used for data communication programs. Checkpoint-ID names a I-O area that contains an Eight-byte value to identify a checkpoint record written to the log file. During recovery, this eight byte Checkpoint-ID is used by IMS to Restart the program.
SYMBOLIC CHECKPOINT CALL
- Can be issued by a BATCH and BMP program
- Apart from committing changes made to the database, it also establishes position in the program from where to Restart, in case the program abnormally terminates.
- The program can also save as many as SEVEN PAIRS of data area along with the checkpoint record. These data areas are restored during the program restart.
- A symbolic checkpoint call works with the Extended Restart (XRST) call to restart the program.
CALL 'CBLTDLI' USING CHKP I-O PCB MASK CHECKPOINT-ID FIRST-AREA-LENGTH FIRST-IO-AREA SECOND-AREA-LENGTH SECOND-IO-AREA ---------- ---------- SEVENTH-AREA-LENGTH SEVENTH-IO-AREA
The I-O PCB mask must be the first PCB listed on the ENTRY statement normally used for data communication programs having a format different from that of database PCB. The CheckPoint-ID names a I-O area that contains an Eight-byte value to identify a checkpoint record written to the log file. Now follows, upto SEVEN PAIRS of field names defined in the working storage of a program the contents of which is to be saved along with the checkpoint record. In each pair the first item contains the length of the datarea to be saved, defined as a Binary field of Full word Type PIC S9 (5) comp, the second field is the name of the data area storing the contents to be saved. For example
01 FIRST-IO-AREA 05 VALID-TRANS-COUNT PIC S9(5) COMP-3 (3 BYTES) 05 INVALID-TRANS-COUNT PIC S9(5) COMP-3 (3 BYTES) 05 CROSS-SALES-VALUE PIC S9(7) V99 COMP-3 (5 BYTES) 01 FIRST-AREA-LENGTH PIC S9(5) COMP VALUE + 11
RESTART CALL (XRST)
- The program that issued a symbolic checkpoint CHKP call must issue a restart call (XRST).
- The XRST call, which is issued only once, does not have to be the first call issued in the program, though it must be issued before any CHKP call.
- Whether a program is to be restarted or not is determined by DL/I with the help of PARM parameter specified in the EXEC statement for the program in the execution JCL, or the CheckPoint ID provided in the Restart Work Area
- If a program is to be Restarted, the XRST call indicates that the following checkpoint call is a symbolic checkpoint.
- Any calls issued before the XRST call are not within the scope of Restart.
CALL 'CBLTDLI' USING XRST I-O PCB MASK Longest Segment Length Restart-Work-Area First-Area-Length First-IO-Area ---------- ---------- Seventh-Area-Length Seventh-IO-Area
The I-O PCB Mask must be the first PCB listed on the ENTRY programs having the longest segment length is the name of a Full Word Binary field of PIC S9(5) comp that contains the length of the longest segment area or path of segments the program processes. DL/I uses this value to acquire the buffer area during a program restart. The restart work area must be set to BLANKS if the program us not to be Restarted. However, a Restart is performed when the Restart Work Area is not blanks or the Checkpoint-ID to be used is provided by the PARM parameter specified in the EXEC statement for the program in the execution JCL, in which case IMS places the Checkpoint-ID value in the Restart Work Area automatically. The total number of I-O areas specified in a call must be less than or equal to the number of areas specified in the CHKP call and IMS restores only those areas within the program during a program Restart.
ROLLBACK CALLS (ROLL AND ROLB)
When issued, will backout all the database updates made by the program since the most recent Checkpoint. This will nullify the effect of any incorrect processing done by the program.
- When issued, the program is Abnormally Terminated with a user Abend code of 0778
- It also deletes any messages for the program that have been retrieved from the message queue since the last checkpoint before termination.
- It can be issued in a Batch program
CALL 'CBLTDLI' USING ROLL
The only parameter specified in the call is the function.
- Following the call statement for further processing
- It can be issued in a Batch program
CALL 'CBLTDLI' USING ROLB I-O PCB MASK
- When issued, Dequeues all the segments, which have been Enqueued by the call using a 'Q' command, code. Q command code is used to establish an Exclusive control over a segment by your program preventing others from updating the segment until your program has released the exclusive control. This will ensure that the segment control will maintain the same data whenever retrieved by the program till it is released.
- DEQ call may be issued for each class from A thru J
- DEQ call releases all the retrieved segments using the 'E' command code, except those
- Segments modified by the program until the program issues a checkpoint.
- Segments required to keep the position in the hierarchy until the position is moved to another record.
- Class of segments that has been locked again as another class.
CALL 'CBLTDLI' USING DEQ I-O PCB MASK I-O AREA
The I-O area is the name of one byte field that contains a one letter character code from A thru J. This represents the segments being Dequeued.