Principle--er model and relational model of database system

The database system is one kind of software, the database system naturally also has his own life cycle--the lifetime. Its lifetime begins with planning, until it is uninstalled. Its intermediate process is very complex, in order to realize the user's idea, the database personnel will abstract the real life data, then in the classification and the operation, lets the data after the integration together, encapsulates them as a system lets the user use it, finally the database personnel in the result carries on the maintenance unceasingly, This not only satisfies the user's needs, but also embodies the idea of serving the people wholeheartedly.

1 The relationship between software and database

The database system is a subclass of software which is an instantiation of the superclass, of course, the software can also be regarded as a strong entity, the database system when a weak body, vulnerable to rely on the existence of strong entities. In the stage of database design, it is a key point that the concept model wants to transform the relational model, the data should be corresponded in the process of transformation, and the data redundancy should be eliminated, of course. In the database design, the database Designer to the real world data and the relationship between data abstraction, respectively, with the entity, contact, attribute three to represent. For the maintenance of the database, it is the most time-consuming and the most troublesome step, after the database is built, it will accompany the database until the old.

2 ER model

Er model consists of entity and relation, entity is abstract in real life, and information transmission between entity and entity is realized by contact. A property is a business card that the entity shares with the contact. Attributes are categorized as simple and composite properties, with single-valued and multivalued properties, and stored and derived properties. In the composite attribute, there is a certain logical dependency between the various attributes, or a hierarchical relationship, such as the book address attribute, it can be divided into provinces, cities, counties ... The confrontation attribute does not have a certain connection between them, such as a degree, it can have a master, PhD, bachelor and so on.

The operation of the ER model is actually the operation of the ER model element, which is the operation between the entity, the relation and the attribute, and the purpose of the operation is to realize the requirement of the user while reducing the redundancy of the data.

Transformation of 2 ER model to relational model

The transformation from the ER model to the relational model is to further organize the abstract data so that the data can be presented in a two-dimensional form after the conversion, so that the data is saved in the database. Database we operate on the data.

Er model is a method and tool for people to know the objective world. The relational model is the product of transforming the ER model into the DBMS world. They are designed to continue to meet the needs of users of the embodiment.

Principle--er model and relational model of database system