Data Model is an abstraction of data characteristics, which describes the static characteristics, dynamic behaviors and constraints of the system from an abstract level.
Provide an abstract framework for the information representation and operation of the database system.
The content described by the data model has three parts, namely data structure, data operation and data constraint.
The data model is a tool used to abstract the real world in database design, and it is a formal framework used to provide information representation and operation methods in a database.
The data model is the core and foundation of the database system.
In fact, it is a form of ER diagram.
There are three common data models: hierarchical model, mesh model and relational model.
The relationship is actually the meaning of a two-dimensional table, the rows and columns correspond, similar to the meaning of y and x, and the relationship is similar to the meaning of the functional relationship of f(x).
The hierarchical model and the mesh model are easy to understand, just look at the figure. Mainly talk about the relational model.
Hierarchical model:
Mesh model:
The connection between things in the real world is more non-hierarchical. It is not intuitive to express this relationship with a hierarchical model. The network overcomes this drawback and can clearly express this non-hierarchical relationship.
Features of the relational model:
(1) The data structure is single. In the relational model, both entities and the connections between entities are represented by relationships, and the relationships correspond to a two-dimensional data table, with a simple and clear data structure.
(2) The relationship is standardized and established on a strict theoretical basis. The basic norms that constitute a relationship require that each attribute in the relationship be indivisible, and the relationship is established on the basis of strict mathematical concepts with a solid theoretical foundation.
(3) The concept is simple and the operation is convenient. The biggest advantage of the relational model is its simplicity, which is easy for users to understand and master. A relation is a two-dimensional table, and users can operate the database with a simple query language.
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We already know that relational databases are built on relational models.
The relational model is essentially a number of two-dimensional tables storing data, which can be regarded as many Excel tables.
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