About the different access modes

When your database is allocated to an online system, you access it in BMP mode. BMP mode provides strict controls that are suited to live production environments. For example, you can only access those database data sets that have been defined for your IMS subsystem. Any changes that you make are logged in the IMS online log data set and IMS controls such things as multi-user access to the segment data and automatic backouts if needed.

When running in BMP mode, you can choose to access the database using a Static PSB or a Dynamic PSB. Static PSBs provide control over what segments are available and what processing options, such as Browse or Edit, can be performed on the available segments. Typically, an end-user who updates data in a live production environment would access a database in BMP mode using a Static PSB.

You can also use Dynamic PSBs in BMP mode, if your site installation has been set up to allow this type of access. Because this combination provides full access to live data, some sites may choose not to enable it. Dynamic PSBs are generated by FM/IMS from the specified DBD and allow both Read and Update access to all segments in a database (PROCOPT=G or GO for Browse and PROCOPT=A for Edit). This type of access might be required by a Database Administrator who wants to make critical changes to live data, without having to bring the entire IMS subsystem offline.

Note: To allow the use of Dynamic PSBs in BMP mode, your FM/IMS administrator must have followed the setup process, as explained in the Customization Guide.

When your database is offline, you access it in DLI mode. In DLI mode, you must specify the data sets that you want to access and security is controlled at the data set level, that is, if you have access to the data sets via ISPF, you can access them via FM/IMS in DLI mode. These data sets are allocated to your TSO address space. This type of access is typically used by developers. While DLI mode usually provides single user access, you can share databases with other users by working with the IRLM option turned on (depending on your IMS subsystems definitions).

In DLI mode, you can use a Static PSB or a dynamic PSB. Static PSBs provide the same measure of control in DLI mode as that given in BMP mode. Using a Dynamic PSB in DLI mode requires no special set up at installation time and allows you to have full access to the data sets you have specified.

Note: You can also control the type of read provided in the Browse, Extract, Print, and Batch Browse functions by changing the PROCOPT settings (PROCOPT=G for normal read, PROCOPT=GO for read without integrity) on the DLI Mode Options panel (option 0.6.4) or BMP Mode Options panel (option 0.6.6).

A setting of G means that database read locks are set and released as you read the data, ensuring that you are always reading the complete updated database record.

A setting of GO means that no locks are set, which can result in internally inconsistent segments (with different parts of the segment updated by two different units of work).