CA IDMS VSAM Transparency Architecture › Request Processing Modules › The CA IDMS VSAM Transparency Back End

The CA IDMS VSAM Transparency Back End

The CA IDMS VSAM Transparency back end accepts requests from the front end and translates VSAM requests to CA IDMS/DB database calls. The back end does the following:

• Initializes the run unit. The back end:
  • Validates open and close requests.
  • Initializes and terminates the back-end control blocks. This includes loading the file management tables, which establish correspondences between VSAM requests and the database, and loading the transaction name table, which establishes correspondences between CICS transactions and CA IDMS/DB subschemas.
• Translates VSAM requests. The back end:
  • Processes VSAM request parameter lists (RPLs)
  • Uses the file management table to convert VSAM requests to the corresponding DML statements
• Accesses the database. The back end:
  • Issues standard DML calls to access the database
  • Receives requested data from the database, including CA IDMS/DB status codes
  • Converts database output to VSAM format
  • Sends the VSAM data and status information to the front-end communication manager routine, which then returns the output to the application program