ISO 2709 - Basic Structure

Basic Structure

A ISO 2709 record has three sections:

• Record label—the first 24 characters of the record. This is the only portion of the record that is fixed in length. The record label includes the record length and the base address of the data contained in the record. It also has data elements that indicate how many characters are used for indicators and subfield identifiers. (See Variable fields, below)
• Directory—the directory provides the entry positions to the fields in the record, along with the field tags. A directory entry has four parts and cannot exceed nine characters in length:
  • Field tag (3 characters)
  • Length of the field
  • Starting character position of the field
  • (Optional) Implementation-defined part
• Datafields (Variable fields)—a string containing all field and subfield data in the record
• Record separator—a single character (IS₃ of ISO 646)

Note that although tags are often displayed as labels on bibliographic fields and each bibliographic field has an associated tag, the tags are stored in the directory not in the bibliographic field.