Introduction

With the FOCUS IMS/DB Interface, you can use FOCUS to access IMS or DL/I databases. (From this point forward, IMS refers to IMS and/or DL/I.) FOCUS is well adapted to the IMS environment and fully supports its data model.

Beginners as well as advanced data processing professionals can take advantage of Interface data retrieval and analysis facilities comprehensive enough to satisfy virtually any requirement. FOCUS file descriptions integrate all facilities and provide transparent access to the underlying data file.

Since IMS and FOCUS both view databases as hierarchical multipath trees, FOCUS concepts map easily to those of IMS. For example, FOCUS represents IMS segments as FOCUS segments and IMS fields as FOCUS fields. You can represent an IMS repeating field as an OCCURS segment. To implement relationships between IMS files dynamically, you can use the JOIN command.

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The Interface provides read-only access to existing IMS databases; as a result, FOCUS features that perform write operations, such as MODIFY and FSCAN, are not supported. The Interface uses only standard IMS read-only calls; it never jeopardizes the integrity of an IMS database. The Interface also supports certain IMS security features and complements existing IMS security. FOCUS DBA security features permit controlled data access at the user, file, field, or field-value levels.

When you issue a FOCUS retrieval request, the Interface translates it into an equivalent set of IMS DL/I (Data Language/I) calls. When the IMS DBMS returns data in response to the request, the Interface passes this data to the FOCUS Report Writer for formatting and, possibly, additional processing. The Report Writer can process data from any FOCUS-readable file. The Interface does not recreate the data in the form of a FOCUS database.

The following diagram depicts report processing:

FOCUS and the IMS DBMS interact as follows:

  1. Given a report request, the Interface builds DL/I calls that define the request in terms the IMS DBMS can understand.

  1. Having received these calls from the Interface, the IMS DBMS retrieves data targeted by the request and returns it to FOCUS.

  2. The IMS DBMS sends records one at a time and/or a return code back to the Interface, which in turn passes it to FOCUS for further processing.

The Interface creates SSAs (Segment Search Arguments) to optimize DL/I calls based on request criteria and thus performs two primary tasks :

Just as important, the Interface initiates and monitors communication between itself and the IMS DBMS and provides descriptive error messages when necessary.

Information Builders