Re-knowledge Database

Haven't summed up the database for a long time, brush up

    What the hell is a database for? To carry out our discussion with this question.

First, Introduction

    The database is developed from the file management system and is the advanced stage of the management of the data. We all know that it is used to store data and can be

  to say that the electronic file cabinet, can be used to increase the deletion of data to check operations, but it is not only to store data, with the database technology

  Databases and large database systems have been widely used.

Two or three floor

    These three layers are the physical data layer, the conceptual data layer, and the user data layer, and think about the three layers of learning now.

      1. Physical data tier: storing the most raw data    can be referenced in the data Access layer (D)

      2. Logical data layer: The overall logical description of all data in a database   can refer to the Business Logic layer (B)

      3. User data layer: Data provided for some specific users    can refer to the presentation layer (U)

    Once again refer to the three layer, three layers between the more entities to achieve the transmission of data, then the database of the three-level between the correlation between

  The joint?

    Mapping

    Maintains data consistency across three tiers of the database through mapping

    The mapping between the user data layer and the logical data layer is generally defined in the user data layer

    The mapping between the physical data layer and the logical data layer time is generally defined in the physical data layer

Third, discuss the merits

    1. Data sharing

       The database contains all the user information, the user can also access the database through the interface, to achieve the sharing of data, such as the interconnection

    Network era of data sharing, almost all information can be found on the Internet

    2. Reduce the Shanyu of data

       When data sharing is achieved, users no longer have to create files separately, reducing the amount of duplicated data

    3. Centralized Data Control

       Use the database to control and manage data centrally, and through the relationship between data model table data

    4. Data security, integrity and concurrency control

       Security: Prevents data loss, error updates, and unauthorized use

       Integrity: Ensure the correct, effective and compatible data

       Concurrency control: Allows multiple users to access at the same time, or prevent the user from not working properly

    5. Failure recovery

       Database management system can detect and repair faults in time and prevent data from being destroyed.

Summary:

    The content of the database is very much, need to study slowly, but can feel the database is playing a more and more important role now

    Learning is not a matter of overnight, but if you look back, there will be more resonance.

Re-knowledge Database