Collection Development may need data about publishers, and so on. Each row is one record, each column is a field, and the table is a collection of records. In these examples, the field names are shown at the top of each column, and data fills the table. The first table, BIB, contains serials bibliographic data. A characteristic of a relational database is that common fields, called keys , link tables together.
Keys are one or more fields that uniquely identify a record.
No two rows may have the same key value. In the BIB table, above, the ISSN is the key. The next table, COPY, contains data about each copy in the library, one row per copy. Observe that ISSN is the common field that links the two tables together. Common fields must contain the same data, but not necessarily have the same name.