Database Systems: Concepts, Design and Applications

3.4. Basic Concept of Files

As explained in Chapter 1, Section 1.2.9, a file is a collection of related sequence of records. As further explained in Sections 1.2.7 and 1.2.8, records are a collection of logically related fields or data items made up of bytes and words of binary-coded information, which are the smallest unit of data that has meaning to its user. One or more data items or fields in a record are unique identifier called key that differentiates between records. For example, model number (MOD-NO) of model record in INVENTORY file and employee number (EMP-NO) of employee record in EMPLOYEE file of Fig. 1.9 (a) and (b), respectively, are the unique identifiers (key) to differentiate between records of these two files. These fields ...