Many users can read and change the same FOCUS database at the same time, through both FOCUS and Host Language Interface (HLI) commands, by using a facility called Simultaneous Usage (SU). In SU, the database is called a centrally controlled database. It exists on a separate user ID called a sink machine or FOCUS Database Server. Users' CMS IDs that are running FOCUS, HLI programs, or batch FOCUS jobs are called source machines or clients. The users (via their source machines) send requests and transactions to the sink machine. The sink machine processes the transactions and transmits the retrieved data or messages back to the source machine.
Note: In the remainder of this manual, the terms sink machine, FOCUS Database Server, and server will be used interchangeably as will the terms source machine, user, and client.
The following figure depicts the SU environment. Three users are executing FOCUS requests. The source machines communicate with the sink machine through the Inter User Communication Vehicle (IUCV). When the sink machine receives a request from a source machine, it changes or retrieves data from the centrally controlled database. The sink machine then transmits the results back to the source machine. Notice that User 3 is also working on a locally controlled database, which is not under SU control.
SU is not necessary if all users are only reading a database (for example, if they issue TABLE requests). SU is needed, however, if one user wants to modify the database while other users are reading it. In that case, all users, even those just reading the database, must use the database in the SU environment.
With the Multi-Threaded SU Reporting Facility, users can read a centrally controlled database without using a sink machine. Operating the Sink Machine, explains how to use the Multi-Threaded SU Reporting Facility.
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