Design of database model in software project document

background: The structural design part of the database design specification of the software project document should understand that the conceptual structure design, the logical structure design and the physical structure design of the database are the conceptual model, the logical model and the physical model of the design database. So. What is the conceptual model, logical model and physical model of a database?

Reflection: The original study of the principles of the database system when the understanding is not very thorough. It's not too late to mend!

Conceptual Model

Official explanation: Conceptual design is based on the user's needs to design the conceptual structure of the database. It expresses in canonical form the understanding of what the user needs to design, and this stage involves terminology: entity, entity set, attribute, entity identifier.

Popular explanation: The concept model is after understanding the user's needs. After analyzing and summarizing, the concept and noun which are used to express user's demand are obtained. such as the computer room fee system "students", "General users", "card" and so on.

At this stage, we can express the entities and attributes by using ER graph and describe the relationship embodied in the narrative e-r diagram by use case diagram.

Attached: The ER pattern should meet the following criteria: The number of entity types should be as small as possible. The entity type contains as few attributes as possible. No redundancy is associated between entity types.

Logical model

Official explanation: The logical design is based on the conceptual design of the results of the design of the logical structure of the database, namely the expression and implementation methods. Logical design can have many different methods. Terms can include: Fields, records, files, key codes, etc.

The logical model is to detail the conceptual model, to realize the relationship expressed in the conceptual model, need the detailed function to deal with, also can be understood as the transformation of the E-r graph to the relational model, on the basis of the conceptual model, the relationship between entities and entities is transformed into relational patterns.

Take the computer room system as an example: "Student" information should basically include: professional name, school number, class, gender and other attributes; "card" information should basically include: card number. Type. Register time, Ischeck and other attributes.

and "orders" to the "customer", "salesman" and "product" details are associated.

        systems need to include several data sheets: Student information sheets, card tables, etc.

        system to include several functions: up and down functions, user registration, query information and other functions.

        All of these are building logical models that simply indicate what the system is implementing. But how to achieve. What tool to implement is not yet spoken. The latter belongs to the physical model range.  

Physical model   physical model on

  The       physical model is based on the above-mentioned logical model and is implemented on detailed physical media. For example, the relational schema in the database with a detailed table written out, is our student_info,recharge_info table and so on.

summary:   of these three processes. is to implement a software system from abstraction to detailed three key steps, from analysis, design, to implementation of the step-by-step process.

Database model design in the software project document