The Access File

In most environments, you select a PSB prior to invoking FOCUS. However, if you connect to IMS using the DBCTL environment, you select the PSB during your session, and you have the option of switching PSBs between requests.

You have two options for selecting a PSB within the session:

• You can issue the IMS SET PSB command either from the command line, within your FOCUS or MSO profile, or in a FOCEXEC (see the instructions for implementing DBCTL in Environments).
• You can use an Access File to identify the PSB. Each Access File corresponds to one Master File; it identifies the PSB associated with its corresponding Master File.

If you use an Access File, the Interface identifies the appropriate PSB when you reference a Master File in a request. The selection is automatic and transparent to you.

Each Access File contains one attribute starting within the first eight bytes. The syntax is

PSB=psbname,$

where:

psbname

Indicates the name of the FOCPSB library member to use. This name must be identical to the name of the actual PSB that IMS will access. If the member does not exist, the following error message is generated:

(FOC4261) FOCPSB MEMBER NOT FOUND: psbname

Access Files are members of a partitioned dataset. The member name of an Access File within its partitioned dataset must be the same as the member name of the corresponding Master File within its partitioned dataset. At run time, the Access File dataset is allocated to ddname ACCESS. (This allocation is optional if all PSB selection is dynamic.)

Note:

• All participating files in a join must use the same PSB. Any attempt to join files that require different PSBs generates the following error message:

(FOC4295) ACCESS POINTS TO DIFFERENT PSBS IN JOIN

• The IMS SET PSB command supersedes the PSB attribute in the Access File.

The following is a sample Access File corresponding to the DI21PART Master File. The Access File is member DI21PART in the Access File library:

PSB=FOCSD,$