DL/I (Data Language/I) is the language used to manipulate IMS databases. You can either access DL/I directly, through the Call-Level interface (Call 'CBLTDLl'), or indirectly, through the High-Level interface (EXEC DL/I). With the call-level interface, your programs call the DL/I program, CBLTDLl, to access and/or manipulate IMS databases. The value of the parameter passed informs CBLTDLl as to what action the programmer wishes it to perform. In high-level interface, instructions are given using EXEC DL/I commands. These commands are converted to calls to the call-level programming interface via a pre-processor.

The high-level interface was developed subsequent to the call-level interface as a way of simplifying the DL/I interface for the IMS programmers. Because of this, it has become the preferred way of accessing IMS databases. You should still be familiar with the call-level interface because there are still many organizations, those do not use the high-level interface. In addition, there are a significant number of programs, which were written prior to the development of the high-level interface.

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