Each field consists of a series of bytes. Record, which is a collection of related data fields describing the subject of the record such as course number, professor's name, and room number. File, which is a group of related records such as a file of all courses offered by the school. Database, which is a group of related files such as the registrar's file, the bursar's file, and the admissions file. Key field provide a means of uniquely identifying records so that they can be located, retrieved, updated, and sorted.
Indexes are listings of key fields showing where the associated records are physically stored.
Without theses tools, it is extremely difficult to utilize stored information. Both ISAM and the random access method allow direct access to individual records. As its name implies, the indexed sequential access method uses an index of key fields to accomplish this. The random access method does not use an index. Instead, it uses a mathematical formula called an algorithm to calculate the physical storage location of a record.