Extracting entity classes and objects

Designers can extract entity objects according to nouns and noun phrases in the text description of use cases 【abbott ,1983】

Another method is based on a predefined conceptual list , Judge whether there is corresponding entity object in the system item by item , This method can be used as a supplement to the first method

For general software systems , In general, the following concepts can be used to find entity objects in the system :

* A physical or physical object
* The role of man
* organization
* time
* place
* Specification or description of the transaction
* Rules and policies
Once the entity classes are found, they can be grouped according to how common they are , To abstract the entity class in the analysis model , However, in the analysis phase, it is difficult to decide whether an entity object should be classified into the same class as other entity objects , Or should it be grouped into a single class as the only object instance , Under this kind of mine robbing , The feasible way to judge is , If several objects have the same properties . Methods and relationships , The value of knowledge implementation varies , Then they should belong to the same object , Otherwise, they should be abstracted into different classes , General experience is to avoid omission , For those who are difficult to identify , They can be grouped together for the time being , Remain in analytical model

Extract attributes :

generally speaking , In object-oriented analysis , Try to use descriptive language to explain the analyzed attributes , Instead of using procedural languages to define properties and their types precisely , When looking for properties of an analysis class , Focus on properties that have simpler data types , If complex properties are found , Either separate this property as a separate analysis class , Either this property can be expressed by analyzing the relationship between classes

Extraction relation :

Analyzing the relationship between classes indicates the relationship between one or more classes , Looking for relationships between analysis classes : In the text description of the use case , Verbs and verb phrases that represent the relationship between two nouns can help us determine the relationship between analysis classes . for example “.... Yes ”
“ yes ............ Part of ” All of them reveal the relationship between classes or objects more or less
* Normally , The relationships between classes are as follows :
* One to one relationship : Indicates that there is a one-to-one correspondence between two classes
* One to many relationship
* Many to many relationship
* Inductive relation : Concepts can be organized into hierarchies , At the top of the hierarchy is the most general concept , The lower level is the concept of gradual specialization , Inductive relation corresponds to inheritance relation in design process