Maria Lourdes C. Capilitan

SysAnal

July 8, 2008

Book Review

Systems Analysis and Design Methods

(Fourth Edition)

Jeffrey L. Whitten, Lonnie D. Bentley

QA 76.9 S88 W48 1998

Quote(Chapter 5): Data Modeling as systems analysis tool. The proper way of using a modeling tool, entity relationship diagrams, document data that must be captured and stored in a system, independently of showing how data is used. Relationships are business associations that exist between one or more entities. Entities are described by their degree and cardinality.

Cardinality Notations

Cardinality shows degree of each relationship. It also defines the minimum and maximum number of occurrences of one entity for a single occurrence of the related entity.  It must be defined in both directions for every relationship.

A Recursive Relationship

Degree of a relationship is the number of entities that participate in the relationship.

The  recursive relationship exist between different instances of the same entity. It is also called as Unary relationship.

            N-ary relationship (tenary relationship) it is the relationship exist between more than two different entities.

            Associative entity an entity that inherits primary key from more than one other entity. Each part that concatenated key points to one and only instance of each connecting entities. Can be describe by its own non key attributes. It is used to represent a logical association between two or more entities.

Foreign Keys

Foreign keys is a primary key of one entity that is contributed to another entity to identify instances of a relationship. It always matches the primary key.

Nonspecific Relationship is one in many instances of one entity are associated with many instances of another entity. It can be resolved into a pair of one-to-many relationship. It should be used only in the early stages of data model.

Generalization it is an approach that seeks to discover and exploit the commonalties between entities. It is a technique where the attributes are common to several types of an entity are group into their own entity and called as super type.