USES OF DATA DICTIONARIES IN SYSTEMS ANALYSIS
The logical design for a database system shows the grouping of users by organizational structure. In a logical design, the principal concerns are the relationships among the users of the system. The logical design for the system is reflected in an Entity Relationship Diagram (ERD) that is presented as a database schema. It is composed of entities, attributes, and relationships (Dennis & Wixom, 2003).
Entities are the people, places, things, actions, and concepts relevant to a system. Attributes are the data elements that describe the entities (Dennis & Wixom, 2003).
Relationships are the connections that exist among entities. Relationships may be (a) one-to-one, (b) one-to-many, and (c) many-to-many. Many-to-many relationships in a system are undesirable because they tend to confuse relationships within a system (Dennis & Wixom, 2003).
Database management systems may be structured to express the relationships between the data contained in the databases in one of three logical data structures or models (Kendall & Kendall, 1999). These functions are accomplished as follows:
1. Hierarchical structure. In this structure, the relationships between records form a hierarchy or tree structure. In this structure, also, all records are dependent and are arranged in multilevel structures consisting on one root record and any number of subordinate levels. All data relationships in this structure are one-to-many, as each data element may be related to several other data elements below in the hierarchy, but may be related to only one data element above it. The data level at the highest level of a hierarchy is called the root record, and this root record is the point of entry into the hierarchy. Data elements are stored and located by moving progressively downward from the root to the subordinate data elements until the desired data element is located.
2. Network struc...