A SESAM/SQL application program is not able to access the data in a database directly. Instead, access to the data in a database is provided by the Data Base Handler (DBH). In conjunction with connection modules, the DBH provides an interface between the application program and the database.
The DBH performs the following tasks:
it analyzes the statements from the application programs, determines the optimum access method and executes the statements
it passes the results of database operations back to the application program
it monitors all database activity
it controls the service tasks for utility functions
it logs important information on database activity in DBH-specific log files)
it reports any errors that occur
Working with multiple databases
The SESAM/SQL-DBH supports operation with multiple databases. It can handle as many as 254 databases in parallel. Which means that each individual application program can access as many as 254 databases. If this proves to be insufficient in large applications, implementation of the SESDCN distribution component should be considered (see section “Distributed processing with SESAM/SQL DCN”).
Working with multiple requesters
Multiple requesters can work simultaneously with the SESAM/SQL database. Simultaneous access to the database by multiple requesters is managed and coordinated by the DBH.
SESAM/SQL allows an optional number of requesters. In timesharing, a requester is either a batch or an interactive program, a terminal or a pair consisting of the user ID and the terminal.