CA IDMS databases are accessed using a Data Manipulation Language (DML). DML is a sub-language that is imbedded within another host language, such as COBOL or PL/I. Since the host-language compiler does not understand DML, a program containing DML must be pre-processed using a CA-supplied pre-compiler. The pre-compiler converts the DML requests into host-language statements that result in a run-time call to CA IDMS.
There are two types of CA IDMS database environments: local mode and central version.
Local Mode
Local mode is a single-user environment providing database services to just one application. Only batch application programs can access a database in local mode. The CA IDMS database manager (DBMS) executes within the same address space as the batch application program as illustrated in the following diagram.
Central Version (CV)
Batch applications may and online applications always access CA IDMS databases in central version mode. A central version environment supports concurrent access from multiple applications, controls concurrent use of resources, and provides automatic data recovery in the event of failure. The following diagram illustrates both an online and a batch application accessing a database through a central version that is a component of a DC/UCF system.
Any number of local mode or central version environments may be active within an operating system at one time.
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