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Most fields contain several related pieces of data. Each type of data within the field is called a subfield, and each subfield is preceded by a subfield code. Subfield codes are one lowercase letter (occasionally a number) preceded by a delimiter symbol.
A delimiter is a character used to separate subfields. Each subfield code indicates what type of data follows it.
In the following example, the field for an authorized personal name is defined by the tag 100. This field includes 3 subfields with subfield codes "a", "q", "d."
| 100 1_ Lawrence, D. H. ‡q (David Herbert), ‡d 1885-1930 |
Subfield "a" is for the personal name itself. The symbol "‡a" usually does not show in bibliographic utilities or online catalogs. The subfield “q” is used for a qualifier, fuller forms of the name given in parentheses. Dates of birth and death go in subfield “d.” |
