chapter 4 types of data models

1 It is a way to visuelise data.

2 It is a concepts for presenting data in ways that are close to the way people perceive data.

3 An entity is the representation of the data in the system. Attributes are parts of an entities data. Relationships represent connections between different entities.

4

• The relational model represents data as relations, or tables. For example, in the membership system at Science World, each membership has many members (see Figure 2.2 in Chapter 2). The membership identifier, expiry date and address information are fields in the membership. The members are individuals such as Mickey, Minnie, Mighty, Door, Tom, King, Man and Moose. Each record is said to be an instance of the membership table.
• The network model represents data as record types. This model also represents a limited type of one to many relationship called a set type, as shown in Figure 4.1.

• The hierarchical model represents data as a hierarchical tree structure. Each branch of the hierarchy represents a number of related records. Figure 4.2 shows this schema in hierarchical model notation.