How DBEngine Works
DBEngine is a host library program that provides several entry points for retrieving both data definition and data records from a DMSII database. To provide this information, DBEngine reads the DMSII DESCRIPTION file, the CONTROL file, and the audit trail. DBEngine uses the services of the Accessroutines to retrieve data from the database for the initial cloning.
Sources of information for database records for DBEngine are as follows:
When an accessory requests a clone (initial extraction), DBEngine reads each record in the specified data set and sends it to the accessory. This is called data set extraction.
DBEngine’s source of information about updates to database records is the DMSII audit trail, which contains before and after images for all changed records. DBEngine reads the audit trail and selects information for data sets the accessory requested. It sends a copy of each updated record back to the accessory. DBEngine processes only closed audit files (unless DATABridge Plus is installed or the Read Active Audit option is set to true); it does not access the current (in use) audit file.
DBEngine initializes when the Server Accessory and other accessories call it (a single copy of DBEngine is linked to each accessory). DBEngine shares the same code stack as other copies of the engine, but it does not share the same data stack.