Environments

• FOCUS can run in a separate address space from all IMS components and pass its DL/I calls to either the IMS region controller (DFSRRC00) or the CICS region controller (DFHDRP) in a second address space.

  To initiate this configuration, you execute either program DFSRRC00 or program DFHDRP. This region controller program then loads the XMI server (program XMI). After the XMI server is loaded and executing, you can invoke the Interface from a CLIST or batch JCL. In order for the FOCUS address space to communicate with the region controller address space, you must allocate a common communication file in each. See Access to IMS Through the XMI Server, for information about the XMI server environment.

Note:

• In prior releases, the BMP extension (program FOCBMP) served the function now performed by the XMI server. In Release 7.0, by default you access the XMI server, described in this chapter. For information about accessing the BMP extension, see Release Dependent Interface Features.
• IMS Version 5.1 does not support program DFHDRP. It supports access via DBCTL.

This is the required configuration for accessing IMS databases from CICS; for information about access from CICS, see Release Dependent Interface Features.

This configuration supports access from MSO.

• FOCUS can run in the same address space as the IMS region controller.

To invoke the Interface with this configuration, you execute either program DFSRRC00 (for IMS). This region controller then loads FOCUS.

Access to IMS databases with this configuration is quick, eliminates the separate FOCUS address space needed with the XMI server, and does not require you to allocate a communication file. However, it is not available through MSO or CMS. In addition, IMS or CICS must allow shared access to the databases. See Access to IMS With FOCUS Loaded by the Region Controller, for information about this environment.

Note: IMS Version 5.1 does not support program DFHDRP.

Access to IMS Through DBCTL, Access to IMS Through the XMI Server, Access to IMS With FOCUS Loaded by the Region Controller, discuss each environment and provide CLISTs and JCL for invoking the Interface. For your convenience, Summary Chart, contains a chart that summarizes the environments available with the Interface, including the advantages and disadvantages of each. Environment Switching, explains how you can change from one environment to another within your session.

Several of the environments through which you can invoke the Interface provide access to Fast Path databases (see the summary chart in Summary Chart). If your site accesses Fast Path, it should have included certain parameters in the IMS control region startup procedure. You may need to know the values of the following parameters in order to access Fast Path through the Interface:

Parameters	Definition
BSIZ	Specifies the size of the Fast Path buffer. It should be large enough to handle the largest Fast Path record.
DBBF	Specifies the number of buffers (of size BSIZ) to be allocated. A formula for calculating DBBF follows this chart.
DBFX	Number of DBBFs IMS should page fix at startup time.

When you access Fast Path databases through the IMS region controller program, DFSRRC00, you specify two additional parameters: NBA (Normal Buffer Allocation, the number of DBBFs that the DFSRRC00 region can use) and OBA (Overflow Buffer Allocation, the number of DBBFs that the DFSRRC00 region can use as overflow buffers). Initiating the XMI Server in BMP Mode: PARM='BMP,XMI,psbname', and Invoking the Interface in BMP Mode: PARM='BMP,FOCUS,psbname', discuss these parameters.

When you access Fast Path DEDB databases from the DBCTL environment, the CNBA parameter (included in the DRA Startup Table, discussed in Installation Instructions) identifies the number of Fast Path NBA buffers.

DBBF is determined by the following formula:

DBBF = CNBA + NBA + OBA + DBFX + (a 20-30% cushion)

Technically speaking, the Interface is not an IMS transaction, since it does not communicate through the IMS message queues and, therefore, does not require an IMSGEN. The PSB you use should specify PROCOPT=GO to inform IMS that the records returned to this program need not be enqueued; in the event of a failure of the IMS/DC region, the restart processing can ignore this program. PROCOPT=GO indicates read without integrity; that is, you may not get the most recent update.

Note, however, that the PROCOPT actually specified in the PSB, or in the PCB itself, is transparent to the Interface and has no effect on its retrieval logic. Therefore, you can actually use any PROCOPT. If you use PROCOPT=A, indicating all rights, you may get locked out while another user updates the database; also, IMS will use additional time and resources to check whether you updated the database, an operation not available through the Interface.