How Applications Share Data | An Introduction to IMS: Your Complete Guide to IBMs Information Management System

To understand data sharing, you must understand how applications and IMSs share data.

The processing options for an application program are declared in the PSB and express the intent of the program regarding data access and alteration. The processing options are specified with the PROCOPT keyword as part of the group of statements that make up the program communication block (PCB) for a particular database access. The PCB declaration implies a processing intent.

If the application program is to insert, delete, replace, or perform a combination of these actions, the application program is said to have update access. An online program that has exclusive access, specified as PROCOPT=E, is interpreted as having update access.

Programs that need access to a database but do not update the data can do so in two ways. They can access the data with the assurance that any pending changes have been committed by the program that instigated the change; this is termed read access (PROCOPT=G). Alternatively, programs can read uncommitted data, if the program does not specify protection of data status. This is termed read-only access (PROCOPT=GO).