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Version: 3.1.X

Physical Database Architecture

ABCD uses the CISIS technology (compatible with CDS/ISIS). A "Database" in ABCD is not a single file, but a collection of related files with the same name but different extensions.

Core Files​

For a database named users, you will find the following files on the server disk:

Master File (.mst)​

  • Purpose: Stores the actual data (content) of the records.
  • Criticality: Extreme. If this file is lost, data is lost.
  • Format: Binary. Cannot be opened with a text editor.

Cross-Reference File (.xrf)​

  • Purpose: An index pointing to the physical location (offset) of each active record in the .mst file.
  • Relation: There is one entry per MFN (Master File Number).
  • Recovery: Can often be reconstructed from the .mst file if corrupted.

Inverted File (.cnt, .n01, .n02, .l01, .l02, .ifp)​

  • Purpose: The search index. Allows fast retrieval of records.
  • Structure: B-Tree structure.
  • Maintenance: Needs to be regenerated (Full Inverted File Generation) if the .mst is updated externally or if the FST (Field Selection Table) changes.

Control Files​

  • Field Definition Table (.fdt): Defines the fields (tags), names, and input types.
  • Field Selection Table (.fst): Defines how fields are indexed for searching.
  • Print Formats (.pft): Scripts defining how records are displayed on screen or print.