In this chapter we will learn:
The discussions of what data items are needed in a system and how they flow; We also discussed how a data dictionary is developed for a system. For designing database we need three things – entities, relationships and attributes. In database design it is necessary to develop a conceptual model of data which specifies the relationships between data. This is used to group data into a number of tables. The tables are organized to reduce duplication of data, simplify functions like adding, deleting and changing data in other words, updating data and select data required for processing, in other word, retrieving data. There is also another functionality of database design is normalization. The methods of organizing or structuring data into tables are known as normalization. The normalized database is later converted to a physical database.
By the end of this chapter we should know:
- The use of entity-relationship modeling to develop a conceptual model of data.
- How to organize the data required in an application as a relation.
- The idea of normalization of relations and the need for normalization.
- The methodology of converting relations to successively higher normal forms.
- Collection of normalized relations as a relational database.
- The use of a method called entity-relationship analysis to obtain a conceptual model of data used in applications.
- The organization of data as relations, normalizing relations and obtaining a relational database.
Entity Relationship Model:
The entity-relationship model for data uses three features to describe data. These are:
- Entities which specify distinct real-world items in an application.
- Relationships Which connect entities and represent meaningful dependencies between them.
- Attribute which specify properties of entities and relationships.