Question

Describe the steps involved in converting an entity-relationship diagram to a set of normalised tables.

Answer 1

Data modeling is an iterative process. Generally a preliminary data model is constructed which is then refined many times. There are many guidelines (rules) for refining an ERD:

1.)Transform attributes into entity types. This transformation involves the addition of an entity type and a 1-M (one-to-many) relationship.
2.)Split compound attributes into smaller attributes. A compound attribute contains multiple kinds of data.
3.)Expand entity types into two entity types and a relationship. This transformation can be useful to record a finer level of detail about an entity.
4.)Transform a weak entity type into a strong entity type. This transformation is most useful for associative entity types.
Add historical details to a data model. 5.)Historical details may be necessary for legal as well as strategic reporting requirements. This transformation can be applied to attributes and relationships.
Add generalization hierarchies by transforming entity types into generalization hierarchy.
Application of normalization principles toward ERD development enhances these guidelines. To understand this application

(i) Representation of dependency concepts in an ERD is outlined, followed by:

The attributes of a table is said to be dependent on each other when an attribute of a table uniquely identifies another attribute of the same table.

(ii) Representation of normal forms toward the development of entity type structure. Guidelines for identification of various dependencies is avoided in the paper so as to focus more on their application. Only the first four normal forms and the Boyce-Codd normal forms are considered.

Normalization rules are divided into the following normal forms:

First Normal Form
Second Normal Form
Third Normal Form
BCNF
Fourth Normal Form.