Requirements and business model analysis requirements 13 data modeling

Book13- Data modeling

1. summary

1. Data modeling describes the definition of data 、 Structure, relationship and other characteristics of technology .
2. Data model performance
   1. Conceptual data model ： Explain the data model in problem domain language , Student ( Student number 、 full name 、 Date of birth )
   2. Physical data model ： The physical data model is an explanation of the solution system language of the data model , Describe the implementation of shared transaction in solution system , Is a formal definition ,Student{(Number,Long,Not Null, primary key),(Name, Varchar 50, Not Null),(Birthday,Date, Null)}.
   3. Logical data model ： Student =( Student number , identifier )+( full name ,4 Chinese characters )+( Date of birth , date )
3. The most commonly used are entity relationship diagrams

2. entity model

2.1. Entity

1. Logical entity is the refinement of conceptual entity , Have a complete description of the characteristics .
2. Entities in entity relationship modeling generally refer to logical entities .
3. Process entities ： For example, sales behavior process entity .

2.2. attribute

1. Above picture email Is a multivalued attribute .
2. Store attributes and export attributes .

2.3. Relationship

1. The degree of the relationship ： Number of entities participating in the relationship

2. Cardinality of the relationship ( constraint )： Describe the number of relationships that the example may participate in
   1. maximum cardinality ： Key constraint
      1. One 1
      2. Many >1
   2. Minimum cardinality ： Participate in the constraints
      1. Optional 0
      2. Mandatory 1

3. Subtype relationships ： Multiple entities are mostly similar 、 A few are different .

4. Entities affected by relationships
   1. Weak entity ： The existence and identification of entities that need to depend on other entities , For example, examination. ( Weak entity ) For the course ( Parent entity ).
   2. Related entities ： The entities attached to the relationship

3. Creation of entity relationship diagram

3.1. Create an entity relationship diagram that fully describes the information

1. Where sufficient information is available
   1. The system is small and simple
   2. The system functions are divided into simple parts , To a certain part
2. step
   1. Identify entities from description information
   2. Identify the identifier of the entity
   3. Establish relationships between entities
   4. Add detailed description
3. example ： textbook 330-332

3.2. Create according to entity relation diagram of hard data form

1. Creating steps
   1. Analyze form content , Determine form subject
   2. Establish relationships between topics
   3. Organize form items around forms
   4. Supplement the details of the entity relationship
2. Example ： textbook P333-335

3.3. Entity relationship diagram creation in complex situations

1. Discover the conceptual domain of the system
2. Create a description of the concept domain
3. Expand concept fields
4. Merge local data models of conceptual domains

4. Relation between entity relation diagram and process model

1. Technology to synchronize entity relationship diagram and process model ： function / Entity matrix .

2. Build functionality / The entity matrix process is also an excellent check , It can help to verify the correctness of process model and data module , Find the mistake 、 missing 、 Redundancy and inconsistency .