There are two techniques used for the purpose of data base designing from the system requirements. These are:
• Top down Approach known as Entity-Relationship Modeling
• Bottom Up approach known as Normalization.
we will focus on top down approach of designing database. It is a graphical technique, which is used to convert the requirement of the system to graphical representation, so that it can become well understandable. It also provides the framework for designing of database.
The Entity-Relationship (ER) model was originally proposed by Peter in 1976 as a way to unify the network and relational database views. Simply stated, the ER model is a conceptual data model that views the real world as entities and relationships. A basic component of the model is the Entity-Relationship diagram, which is used to visually represent data objects. For the database designer, the utility of the ER model is:
• It maps well to the relational model. The constructs used in the ER model can easily be transformed into relational tables.
• It is simple and easy to understand with a minimum of training. Therefore, the model can be used by the database designer to communicate the design to the end user.
• In addition, the model can be used as a design plan by the database developer to implement a data model in specific database management software.
Advantages and Disadvantages of E-R Data Model
Following are advantages of an E-R Model:
• Straightforward relation representation: Having designed an E-R diagram for a database application, the relational representation of the database model becomes relatively straightforward.
• Easy conversion for E-R to other data model: Conversion from E-R diagram to a network or hierarchical data model can· easily be accomplished.
• Graphical representation for better understanding: An E-R model gives graphical and diagrammatical representation of various entities, its attributes and relationships between entities. This is turn helps in the clear understanding of the data structure and in minimizing redundancy and other problems.
Disadvantages of E-R Data Model
Following are disadvantages of an E-R Model:
• No industry standard for notation: There is no industry standard notation for developing an E-R diagram.
• Popular for high-level design: The E-R data model is especially popular for high level.