CDM of Data room Charging System

In the process of writing documents, there must be a system database design. How should we design the database? First, let's explain a concept:

CDM: The concept Data Model (CDM) is used to design the process from the concept layer. In the concept layer, you do not need to consider the actual physical implementation details. CDM describes the overall logical structure of the database. It is independent of any software or specific data access structure and can provide a formal description of the business requirements in the requirement specification. Its main functions are:

① Graphically describe the data organization structure;

② Verify the validity of the data structure;

③ Generate the Physical Data Model (PDM, Physical Data Model) for the Physical implementation of the database in the detailed design phase.

Obviously, the first step in database design is the design of CDM. CDM is an abstraction of the real-world data features. It should meet three principles:

1. Ability to simulate the real world

2. easy to understand

3. Easy to implement by Computer

CDM is based on the Entity-RelationShip (E-R) theory, and expands the theory to some extent, from the user's point of view, information modeling, it is mainly used for Conceptual Design of databases.

In general, people abstract the real world into the concept world, and then the concept world into the machine world. In other words, they first abstract objective things in the real world into entity and relationship, it does not depend on a specific computer system or DBMS system. This is the so-called CDM design. Then we will convert CDM to a data model supported by a DBMS, that is, CDM-> PDM.

CDM is a set of strictly defined model elements that accurately describe the static characteristics, dynamic characteristics, and constraints of the system, including the data structure, data operation and integrity constraints.

What is the specific CDM diagram like? I will share with you an instance: the CDM diagram of the data center charging system.

The software I use is PowerDesigner12.5. This is a powerful software of Sybase. It can draw various diagrams. You can find it online for detailed instructions.

The entity type represented by the square diagram, and the elliptical type indicates the relational type.

Of course, the figure above is not perfect, and many things are not written, just to give everyone an intuitive understanding, that's all.