Database Concepts › Data Structure Diagrams › Representing Records Graphically

Representing Records Graphically

The following information about each record type is included in the data structure diagram of a database:

• Record Name- The name of the record type.
• Record Identification (Record ID)-The identification number of the record type. Each record type in the database is assigned a number that is unique across all record types assigned to the same area.
• Record Format- The format of occurrences of the record type:
  • Fixed (F)- all occurrences have the same length
  • Variable (V)- occurrences vary in length
  • Fixed compressed (FC)-all occurrences logically have the same length, but their contents are compressed when stored in the database
  • Variable Compressed (VC)-occurrences vary in length and are compressed

    Note: CA IDMS supplies routines for compressing and decompressing database records. All compressed records are treated internally as variable length even if their record definition appears to be fixed in length. FC (fixed compressed) records are returned to the program as fixed-length records and VC (variable compressed) records are returned as variable-length records.

• Length- The actual data length (in bytes) for fixed length records; for variable length records, the maximum or average length of the record.
• Location Mode- The location mode for the record type:
  • CALC
  • VIA
  • DIRECT

  See Location Mode for a discussion of these options.

• CALC Key or VIA Set Name- For CALC records, the name(s) of the element(s) that form the CALC key; for VIA records, the name of the set through which record placement is determined; for DIRECT records, blank.
• Duplicates Option- For CALC records, one of the following options:
  • DN (duplicates not allowed)
  • DF (duplicates first)
  • DL (duplicates last)
• Area Name- Name of the area in which the record occurrences are stored.

The DEPARTMENT record type within the Commonweather database is graphically represented by the following figure. From the diagram it can be determined that its location mode is CALC using DEPT-ID-0410 as a CALC key whose values must be unique. It is a fixed length record in which every occurrence contains 56 bytes of data. Its internal numeric identifier is 410 and DEPARTMENT record occurrences are stored in the ORG-DEMO-REGION of the database.