LIM, MARYLYN GRACE C.

OOA

            Book: Systems Analysis and Design: an Active Approach

            Author: George M. Marakas

            Reference No.: QA

                                    76.9

                                    S88

                                    M37

                                    2001

Chapter 6: Modeling the Data Conceptual & Logical Data Modeling

Quote: “Man is a tool-making animal.”

Review:

            This chapter talks about data modeling. Data modeling illustrates the nature of the data used by a system in terms of the rules and their relationship by which it operates. In data modeling, there is one most common format being used, and that is ERD. ERD represents the conceptual data requirements for the proposed system that identity the rules and interrelationship among data. In ERD, there are 5 basic symbols used for constructing entity-relationship diagrams. 1.) Entity. This is represented by a rectangle. Entity is any data that the user wants to store. There are 2 important characteristics of entities. A.) Entities can be distinguished from other entities by some set of identifying characteristics or attributes. B.) Entities represent a class of things that can occur more than once with the organization. 2.) Attributes. This is represented by an oval. An attribute contains a characteristics or descriptive property of an entity or a relationship. 3.) Relationship. This is represented with a diamond. Relationship is an association between one or more entities that has interest to the organization. Relationships are identified by 3 basic characteristics of complexity. A.) Cardinality. This indicates the number of times that an entity in a relationship that are associated with each instance of the other entities in that relationship. B.) Optionality. This represents the degree which a relationship is mandatory or optional. C.) Degree. This represents the number of entities participating in a relationship. 4.) Associative entities. This is represented by a rectangle with a diamond in it. Associative entity inherits the primary key from more than one entity. 5.) Multivalued attributes. This is represented with an oval and another smaller oval overlapping it. Multivalued attribute is a special type of attribute; this can take multiple values on a single entity instance.

            In this chapter, you should also remember some key terms like entity type, entity instances and key attributes. Entity type is a collection of entities that share a common property or attribute. Entity instance represents a single, unique occurrence of a member of an entity type. Key attributes identifies and differentiates one entity instance from other possible entity instance of an entity.

            Logical data modeling is the process wherein the initial identification of the component elements of the conceptual date model is change into a useful logical model. The logical data modeling has 3 purposes. 1.) Formal structuring of the data in a more stable and desirable from through normalization. 2.) Development of a data model in a form that allows the actual data needed by the organization. 3.) The development of a data model than can construct a physical database design.

            Lastly, this chapter lets you know if a data model is a good data model. A good data model should consist of 8 characteristics. 1.) pictorial 2.) rigorous & specific 3.) top-down decomposable 4.) provides focus 5.) minimally redundant 6.) transparent 7.)  easily navigated 8.) predicts the final system.