MY BOOK REVIEW

OBJECT ORIENTED ANALYSIS and DESIGN

Book

Edward Yourdon and Carl Argila

Author

QA 76.64 Y68 1996

Reference no.

CHAPTER 8

God and all the attributes of God are eternal.

-         Spinoza

The attribute layer of the OOA model incorporates both object attributes, as well as relationships between objects instance connection. The objects attributes establish which data are encapsulated in object, object can only do work on those data which they encapsulate. They instance connections, which we will focus on in next chapter, can be thought of as capturing business rules, or application domain constraints. These connections tell us how an object in one class must be related to an object in another class. When these object classes are implemented, these business rules dictate how services must work to be consistent with our established system policies.

Entities contain attributes, which are characteristics or modifiers, qualities, amounts, or features. An attribute is a fact or non-decomposable piece of information about an entity. Later, when you represent an entity as a table, its attributes are added to the model as new columns.

You must identify the entities before you can identify the database attributes. After you determine the entities, ask yourself, "What characteristics do I need to know about each entity?" For example, in an address entity, you probably need information about street, city, and zip code. Each of these characteristics of the address entity becomes an attribute

Earlier we characterized objects as independent, synchronous, concurrent entities which know things. Attributes are the mechanism by which objects know things.

All stored data requirements for a proposed system must appear as object attributes.

Attributes may also be viewed as characteristic of object. There is a distinction between instance attributes and a class attributes. Instance attributes must be applicable and appropriate for each member of a class, they cannot take on value of “not-applicable.” A number of techniques may be used to identify attributes; however, the identification of attributes is an iterative process.