IMS Control Blocks
DC handles information in the form of messages that flow between remote terminals and application programs
Programs and Databases that will run under the control of IMS must be defined in the IMS system definition
Two main categories of resources - Application resources and Data communication resources
Types of IMS DC application programs
BMP: Batch message processing, scheduling by system operator
MPP: Message processing program, scheduled by IMS
IMS/VS forms a layer in between the terminal and the IMS-DC programs, this helps in asynchronous mode of communication. This type of program is called Message Processing Programs(MPPs)
Message - is a unit of data that gets transmitted between a program and a terminal
Primary input to and outputs from DC programs are messages
For each input message, DC program does predictable processing against its databases and sends an output message that to user's screen
The main function of this region is that, all terminal, database, and logging operations associated with IMS-DC programs are performed through this region.
MPP is where IMS schedules and executes message processing program.
The number of MPP regions determines the number of MPPs that can be active at any one time.
A program that occupies an MPP region runs untill it has processed all of the input messages that IMS has received for it. Then it ends, and the MPP region in which it was running is freed and made available for another application program.
A BMP program is much like MPP, except that the terminal response is not required for each input message. the database processing and the input message requires does not have to be done immediately.
They are typicalling batch programs. The main advantage is, it can access databases that are allowed to the IMS control region, for use by MPPs at the same time.
LTERM: For application functions, IMS uses logical terminal names rather than physical names.
Note: within IMS, each LTERM name is associated with one and only one physical terminal. Ex: LDPAYR01
LTERM names are limited to 8 chars
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