USES OF DATA DICTIONARIES The

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

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ated to one another. When using the relational structure, data dictionaries are crucial to smooth functioning of the database system. Defining the structure of the logical relationships between data elements within data bases results in the development of a database schema, which is overall logical or conceptual view of the relationships. Once the schema is designed and documented, sub-schemas must be defined for each of the user application programs that will be used to access the database. A sub-schema is a subset or transformation of the logical view of the data base schema that is required by a specific application program (Hofer, George, & Valacich, 2002). A database management system provides a query language for end users, a data manipulation language for programmers, and a data definition language for control and manipulation of databases within a system. The structure of a database management system may be (as indicated above) hierarchical, with one-to-many relationships, network, with many-to-many relation-ships, or relational, with tabular relationships for very large and complex systems (Hofer, George, & Valacich, 2002). Object-oriented technology has the ability to integrate data and make its use transparent
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