Logical structure design is generally divided into three steps:
1. The logical design of transforming the database from the ER diagram to the relational model is mainly to transform the conceptual model into a general relational model, which is Transform the entities in the ER diagram, the attributes of the entities, and the connections between the entities into a relational model. The following problems will be encountered during the conversion process:
(1) Naming problem. The naming problem can be the original name or another name to avoid duplication.
(2) The problem of non-atomic properties. The problem of non-atomic properties can be expanded vertically and horizontally.
(3) Contact conversion issues. Contacts can be represented by relationships.
2. Optimization of data model The result of database logic design is not unique. In order to further improve the performance of the database application system, the structure of the data model should also be appropriately modified to improve the query speed.
3. Relational view design Relational view design is also called external mode design, also called user mode design, which is a data mode that users can directly access. In the same system, different users can have different relationship views. The relational view comes from the logical mode, but may be different from the logical mode in structure and form, so it is not a simple subset of the logical mode.
The relational view has three main functions:
(1) By shielding the logic mode from the external mode, it provides a certain logic independence for the application.
(2) Better adapt to the different data needs of different users.
(3) Different users have defined different scopes for accessing data, which is conducive to the confidentiality of data.