Figure H-11: Summary of Data Structures and Data Organizations Used for Order Flat Files
As shown in Figure H-11, sequential lists can be stored using any of three file organizations. In practice, however, they are usually kept on sequential files. In addition, although both linked lists and indexes can be stored using either indexed sequential or direct files, DBMS products almost always store them on direct files.
How Can We Represent Binary Relationships?
In this section, we examine how each of the specialized record relationships—trees, simple networks, and complex networks—can be represented using linked lists and indexes.
A Review of Record Relationships
Records can be related in three ways. A tree relationship has one or more one-to-many relationships, but each child record has at most one parent. The occurrence of faculty data shown in Figure H-12 illus-trates a tree. There are several 1:N relationships, but any child record has only one parent, as shown in Figure H-13.
A simple network is a collection of records and the 1:N relationships among them. What distinguishes a simple network from a tree is the fact that in a simple network, a child can have more than one parent as long as the parents are different record types. The occurrence of a simple network of students, advis-ers, and major fields of study shown in Figure H-14 is represented schematically in Figure H-15.
Figure H-12: Occurrence of a Faculty Member Record
Figure H-13: Schematic of Faculty Member Tree Structure
Figure H-14: Occurrence of a Simple Network