Database theory--conceptual model, logical model, physical model

1. Conceptual model

After understanding the user's needs, the user's business areas of work, after analysis and summary, refined to describe the user's business needs some concepts of things.

such as the sales business "customer" and "order", there is "goods", "salesman". The main thing is to extract the concepts in the system (can not include attributes at this time, only entity sets, the analysis structure of the contact set)

The most common representation of a conceptual model is the entity-Relationship Diagram . E-r diagram is mainly composed of three elements of entity, attribute and relation.

A simple generalization, that is--"What is it?"

2. Logical model

The logical model is to embody the conceptual model, that is, to realize what the concept model describes, what specific functions are needed, and what specific information to process, which is the further refinement of the conceptual model.

Also take the sales business as an example: "Customer" information should basically include: unit name, contact person, contact phone, address and other attributes; "Product" Information basically includes: name, type, specifications, unit price and other attributes; "Order" information basically includes: Date and time attributes. and "order" to the "customer", "salesman" and "product" details are associated.

The system needs to establish several data tables: Salesman information table, Customer Information table, Commodity information table, order form.

The system should include several functions: salesman information maintenance, customer information maintenance, commodity information maintenance, the establishment of sales orders.

A simple generalization is--"What to Do"

3. Physical model

　　The physical model is a description of the real database. Some objects in a relational database are tables, views, fields, data types, lengths, primary keys, foreign keys, indexes, constraints, nullable, default values.

Implemented on specific physical media. For example, the database uses SQL Server 2000 so that you can write specific SQL scripts to set up the database on the database server. Including salesman information table, Customer Information table, Commodity information table, order form.

A simple generalization is--"How To Do"

　　Reference reading:

http://blog.csdn.net/lishehe/article/details/24809965

https://wenku.baidu.com/view/8cacb9335a8102d276a22fcf.html

Database theory--conceptual model, logical model, physical model