DB/DC environment

In the DB/DC environment, data is centrally managed for applications that are being executed concurrently and made available to terminal users. Database Recovery Control (DBRC) facilities help to manage database availability, data sharing, and system logging.

The following figure shows an example DB/DC environment.

Figure 1. Example of a DB/DC environment

DB/DC includes: control region, dependent regions, databases, terminals, log, DBRC, DRA, and CCTL. MVS console starts control region. MTO starts dependent regions. User terminals enter transactions.

In the figure, DL⁄I is shown as part of the control region, but it does not need to run there. You can run DL⁄I in its own address space.

To understand the DB/DC Environment and how it works, it is important to understand the transaction. The basic unit of work in a DB/DC environment is the transaction. Transaction processing consists of:

Receiving a request for work that has been entered at a terminal. The request is in the form of a transaction code, which identifies the kind of work to be performed and the data needed to do it.
Invoking a program to do the work, and preparing a response for the terminal operator (for example, an acknowledgment of work performed or an answer to an inquiry).
Transmitting the response to the terminal that requested the work.

The simplest kind of transaction involves two messages: an input message from the terminal user and an output message in return. Application programs can also send messages to terminals other than the input source, and they can generate transactions.