Data Language Interface

Article summary

Data Language One (Data Language/I, DL/I, Data Language/One, Data Language/One ) is the language system used to access IBM's IMS databases 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 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 the 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 parameters passed to the stub.…

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