Describing access paths for database files

 

An access path describes how records in a database file are retrieved. You can define the access path for a database file in various ways.

Records in a physical or logical file can be retrieved through an arrival sequence access path or a keyed sequence access path. For logical files, you can also select and omit records based on one or more field values in each record. A key field is a field that is used to arrange the records of a particular type within a file member.

• Using arrival sequence access paths for database files
  An arrival sequence access path is based on the order in which records arrive and are stored in a database file.

• Using keyed sequence access paths for database files
  A keyed sequence access path is based on the contents of the key fields as defined in data description specifications (DDS).

• Using existing access path specifications
  You can use the Reference Access Path Definition (REFACCPTH) DDS keyword to copy another file's access path specifications. After you create the file, the system determines which access path to share.

• Using floating-point fields in database file access paths
  The collating sequence for records in a keyed database file depends on the presence of the Signed (SIGNED), Unsigned (UNSIGNED), and Absolute Value (ABSVAL) keywords in data description specifications (DDS). For floating-point fields, the sign is the farthest-left bit, the exponent is next, and the significant is last.

 

Parent topic:

Setting up database files

 

Related concepts

Access path description