In the process of writing documents, there must be a system database design, so How to design the database? Let me first explain a concept to everyone:
CDM: Conceptual Data Model (CDM) is used to design from the conceptual level Process. Because is at the conceptual level, there is no need to consider the details of the actual physical implementation. CDM describes the overall logical structure of the database. It is independent of any software or specific data access structure, and can formally describe the business requirements in the Requirements Specification. Its main function is:
①Describe with graphics The organizational structure of the data;
②Verify the validity of the data structure性;
③ Generate a physical data model (PDM, Physical Data Model), used for the physical realization of the database in the detailed design stage.
is obvious, the first step in database design It is the design of CDM. CDM is an abstraction of real-world data characteristics. It should satisfy three principles:
1. It can simulate the real world more realistically
2. Easy to understand
3. Convenient for computer implementation
CDM is Based on the Entity-RelationShip (ER) theory, this theory has been extended to a certain extent, and the information is modeled from the user’s point of view, which is mainly used for the conceptual design of the database.
Generally speaking, people abstract the real world into a conceptual world, and then convert the conceptual world into a machine world, in other words, It is to first abstract the objective things in the real world into entities and relationships, and do not rely on specific computer systems or DBMS systems. This is the so-called CDM design, and then we will convert the CDM into a data model supported by a DBMS. That is, CDM—>PDM.
CDM is a set of strictly defined model elements , They accurately describe the static characteristics, dynamic characteristics and constraints of the system, including three parts: data structure, data operation and integrity constraints.
Then what does the specific CDM map look like, I Let me share an example: CDM diagram of computer room charging system
The software I use is PowerDesigner12.5, which is a very powerful software from Sybase, which can draw various diagrams. You can find specific usage methods on the Internet, and there are detailed instructions.
The entity type represented by the box diagram, and the elliptical type represents the relationship type.
Of course, the above picture is not perfect, many things have not been written, just to give you an intuitive understanding, only this That’s it