Data Language One (Data Language/I, DL/I, Data Language/One, Data Language/One) is the language system used to access IBM's IMS

database In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases sp ...

s and its data communication system. It is implemented from many languages 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 (; an acronym for "common business-oriented language") is a compiled English-like computer programming language designed for business use. It is an imperative, procedural and, since 2002, object-oriented language. COBOL is primarily us ...

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 Communication Block), and this is used as one of the

parameter A parameter (), generally, is any characteristic that can help in defining or classifying a particular system (meaning an event, project, object, situation, etc.). That is, a parameter is an element of a system that is useful, or critical, when ...

s passed to the stub. Other types of PCB are used to send and receive

transaction processing Transaction processing is information processing in computer science that is divided into individual, indivisible operations called ''transactions''. Each transaction must succeed or fail as a complete unit; it can never be only partially comple ...

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 PL/I (Programming Language One, pronounced and sometimes written PL/1) is a procedural, imperative computer programming language developed and published by IBM. It is designed for scientific, engineering, business and system programming. I ...

, the 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

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);.

References

{{Reflist

External links

Information Management Software for z/OS Solutions Information Center

Data-structured programming languages Data Language One