Data Language Interface
Encyclopedia
Data Language Interface is the language system used to access IBM’s IMS
database
s, and its data communication system.
It is implemented from any language by making calls to a software stub, DFSLI000. This stub has entry points to handle a variety of programming languages e.g. calling CBLTDLI from a COBOL
program. This stub is linked to the calling program, passes on the request to the IMS system, and returns the results and a status code.
In any full-function IMS database, the smallest element that can be retrieved is a segment. Each segment is made up of fields, one of which, typically, will be a key field. The segments are arranged hierarchically in the database, the highest level segment type being a root segment. 255 different segment types, on up to 15 levels, are allowed in any database. A database record consists of a specific root segment and all its dependent child segments — there is no limit to the number of segments in a record, or to the number of records in a database (apart from physical limitations of storage space).
The structure of any database is presented to the application program as a PCB (Program Control Block), and this is used as one of the parameter
s passed to the stub. Other types of PCB are used to send and receive transaction processing
messages, access and write to the user’s VDU
screen, and to print reports etc.
When accessing a database segment the application program also uses an SSA (Segment Search Argument) as a parameter, to specify the segment or segments that it needs. This would typically contain the segment type required, and the contents of any key fields.
For all languages except PL/I
, first parameter in a call is the Function Code — a four character field, examples being: “GU ” (Get Unique), “GN ” (Get Next), “REPL” (Replace), and “ISRT” (Insert). With PL/I, due to the way this language does not mark the last parameter with a '1' in bit 0, the first parameter must instead be a fullword (Fixed Bin(31)) containing the number of following parameters.
A typical call from a COBOL program might be . . . CALL “CBLTDLI” USING GU, Stores-Database-PCB, Stores-Segment-Area, Stores-Root-SSA. The program would then automatically wait till the requested data was retrieved and placed in the Segment-Area. The status code contained within the PCB would be updated with either blanks (if all went well) or some informational or error code.
A typical call from a PL/I program might be . . . CALL PLITDLI(FOUR, GU, Stores-Database-PCB, Stores-Segment-Area, Stores-Root-SSA);
Information Management System
IBM Information Management System is a joint hierarchical database and information management system with extensive transaction processing capabilities.- History :...
database
Database
A database is an organized collection of data for one or more purposes, usually in digital form. The data are typically organized to model relevant aspects of reality , in a way that supports processes requiring this information...
s, and its data communication system.
It is implemented from any language by making calls to a software stub, DFSLI000. This stub has entry points to handle a variety of programming languages e.g. calling CBLTDLI from a COBOL
COBOL
COBOL is one of the oldest programming languages. Its name is an acronym for COmmon Business-Oriented Language, defining its primary domain in business, finance, and administrative systems for companies and governments....
program. This stub is linked to the calling program, passes on the request to the IMS system, and returns the results and a status code.
In any full-function IMS database, the smallest element that can be retrieved is a segment. Each segment is made up of fields, one of which, typically, will be a key field. The segments are arranged hierarchically in the database, the highest level segment type being a root segment. 255 different segment types, on up to 15 levels, are allowed in any database. A database record consists of a specific root segment and all its dependent child segments — there is no limit to the number of segments in a record, or to the number of records in a database (apart from physical limitations of storage space).
The structure of any database is presented to the application program as a PCB (Program Control Block), and this is used as one of the parameter
Parameter
Parameter from Ancient Greek παρά also “para” meaning “beside, subsidiary” and μέτρον also “metron” meaning “measure”, can be interpreted in mathematics, logic, linguistics, environmental science and other disciplines....
s passed to the stub. Other types of PCB are used to send and receive transaction processing
Transaction processing
In computer science, transaction processing is information processing that is divided into individual, indivisible operations, called transactions. Each transaction must succeed or fail as a complete unit; it cannot remain in an intermediate state...
messages, access and write to the user’s VDU
Computer display
A monitor or display is an electronic visual display for computers. The monitor comprises the display device, circuitry, and an enclosure...
screen, and to print reports etc.
When accessing a database segment the application program also uses an SSA (Segment Search Argument) as a parameter, to specify the segment or segments that it needs. This would typically contain the segment type required, and the contents of any key fields.
For all languages except PL/I
PL/I
PL/I is a procedural, imperative computer programming language designed for scientific, engineering, business and systems programming applications...
, first parameter in a call is the Function Code — a four character field, examples being: “GU ” (Get Unique), “GN ” (Get Next), “REPL” (Replace), and “ISRT” (Insert). With PL/I, due to the way this language does not mark the last parameter with a '1' in bit 0, the first parameter must instead be a fullword (Fixed Bin(31)) containing the number of following parameters.
A typical call from a COBOL program might be . . . CALL “CBLTDLI” USING GU, Stores-Database-PCB, Stores-Segment-Area, Stores-Root-SSA. The program would then automatically wait till the requested data was retrieved and placed in the Segment-Area. The status code contained within the PCB would be updated with either blanks (if all went well) or some informational or error code.
A typical call from a PL/I program might be . . . CALL PLITDLI(FOUR, GU, Stores-Database-PCB, Stores-Segment-Area, Stores-Root-SSA);