Implementing database design

In an IMS system in which the IMS management of ACBs is enabled, you can describe the characteristics of your databases and application programs to IMS by using either SQL Data Definition Language (DDL) statements or by coding IMS utility macro instructions. If the IMS management of ACBs is not enabled, you can use only the IMS utility macro instructions.

In IMS, the description of a database is referred to as a database descriptor (DBD). A DBD describes the physical and logical characteristics for each database.

The description of the characteristics of an application program is called a program specification block (PSB). A PSB describes the characteristics of an application program and how the program uses data and terminals. Because a PSB also defines what an application program can see of a database, a PSB is also referred to as a program view.

When the IMS management of ACBs is enabled in an online system, DBDs and PSBs are accessed in the IMS catalog only. Utilities and batch systems can access the DBDs and PSBs from either the IMS catalog or the DBDLIB and PSBLIB libraries if available.

When the IMS management of ACBs is not enabled in an online system, DBDs and PSBs are accessed in the ACBLIB libraries. Utilities and batch systems can access the DBDs and PSBs either from the IMS catalog or the DBDLIB and PSBLIB libraries.

For use during run time, the information from a set of related DBDs and PSBs is combined and converted into application control blocks (ACBs).

In IMS systems that manage ACBs, IMS converts the DBD and PSB information into ACBs for you. In IMS systems that use ACB libraries, you can either build the ACBs by using the ACB Maintenance utility or, for some batch application programs, IMS can build the ACBs dynamically during run time.