Object - Oriented

The basic ingredients The three challenges of object-oriented design are: to identify the objects and classes needed to implement the software; describe the relationships between the identiied objects and classes; deene the behavior of the objects by describing the function implementations of each class. A common guideline used to discover the initial set of objects and classes is to look to the noun phrases and nouns used to describe the system requirements and in the sys-tem's analysis. Boo91]. Walking through scenarios of system usage, focusing on the discovery of the important objects and their responsibilities is an important technique used early in the design process JCJO92, WBWW90]. Having found the important objects, the details of the class relationships and object behavior is developed through a set of interconnected models that capture four dimensions of the software architecture: logical static, logical dynamic, physical static and physical dynamic Boo91]. The logical static model describes the relationships of instantiation (class membership), association, aggregation (part-of) and generalization (is-a). This is called the system object model Col94]. The generalization relationship implies inheritance of attributes and methods. Graphical notations derived from the entity relationship notation for data modeling are frequently used to deene the object model RBP + 91]. Constraints, such as cardinality (for example, one-one, one-many, many-many) that are important to the design are also expressed in the object model. A textual notation derived from Backus-Naur-Form grammars is also used Lie96]. Grammars provide a more concise representation of the class structures.