3.3 Database Architecture: Conceptual Structure Design Phase, Conceptual Structure Design, ER Diagram, Conceptual Structure Design Process
conceptual structure design
The conceptual structure design refers to the product of the requirement specification, and also considers the application requirements in the data. The conceptual design is an abstraction of the real world, and what is obtained is a conceptual model. The conceptual model mentioned in the database actually refers to the ER diagram. , also known as an entity-relationship diagram.
In the conceptual structure design stage, the database management system was not considered during the processing process. It has nothing to do with the database management system, that is, it has nothing to do with the DBMS. No matter it is MySQL, Oracle, etc., no matter what it is, during the design process, the concept The structure design stage is just to abstract the corresponding data into the form of ER diagram for the real world.
After getting the ER diagram, the next step is to enter the logical structure design.
ER图
ER diagram is the abbreviation of entity relationship diagram, E means entity and R means relationship.
An entity is a collection of instances, also called an entity set. It is represented by a rectangle. There is a relationship between two entities and an entity. This relationship will be represented by a diamond. In addition to the entity and the relationship, the corresponding entity will also be connected. , special feature values are recorded, called attributes. Attributes are represented by ellipses, and then the corresponding entities are connected by lines.
An attribute can be an attribute of an entity, or an attribute of the relationship itself.
A link between two different entities:
- One to one (1:1)
- One-to-many (1:n)
- many-to-one (n:1)
- many-to-many (n:m)
Conceptual Structure Design Process
Working on ER diagrams by one person requires too much workload. Therefore, according to the needs, first abstract the data, and then distribute it to different people to design partial ER models, and finally merge them.
Integrated method:
- Multiple partial ER diagrams integrated at one time
- Integrate step by step, integrate two local ERs at a time in an accumulative manner
Integration conflicts and solutions:
- Attribute conflicts: including attribute conflicts and attribute value conflicts
- Naming Conflicts: Including Synonyms and Synonyms
- Structural conflicts: the same object has different abstractions in different applications, and the number of attributes and the order of attributes contained in different local ER diagrams of the same entity are not exactly the same