The explanation of the relevant noun in the introduction of database system

Data: Symbolic records used to describe things, data and their semantics are non-divided

Database: An organized, shareable collection of data that is stored in a computer for a long time

Database system: is a system of computer system introduced into the database, composed of database, database management system, application system, Administrator, user "five parts". The core of database system is database management system, which is based on data model. The database has the characteristics of data structure, high sharing, low redundancy and easy expansion.

Database management system: is a layer of system between the user and the operating system, for the efficient definition, access, operation Management, the establishment of maintenance data. Common SQL Sever with Oracle Company's Mysql,microsoft Company

Data model: Is the abstraction of data characteristics, which is usually composed of three parts, data structure, operation and integrity constraints. There are three main data models in the database: Hierarchical data model, mesh data model and relational data model.

Relational model: Relational model consists of three parts, relational data structure, relational operation set and relationship integrity constraint. Typically, the logical structure of data in a relational model is a two-dimensional table that consists of rows and columns.

Relationship: A relationship corresponds to a table that is usually said

Properties: A column in a table is a property

Domain: The value range of a property

Tuples: A single row in a table is a tuple

Code: An attribute group in a table that uniquely identifies a tuple

Candidate code: If the attribute/attribute group K determines (function dependent) The relationship R (can uniquely determine a tuple), then the candidate code called K R

Component: A property value in a tuple

Relationship pattern: A description of a relationship, typically: a relationship name (attribute 1, attribute 2, ..., attribute N)

Three-level schema structure in the database: External mode (also known as user mode, which can see the logical structure of local data currently in use), patterns (also called logical

Schema, which is the description of the logical structure and characteristics of all data in the database), internal mode (also known as storage mode, is the representation of data within the database system)

Data independence: Data independence includes the physical independence of data and the logical independence of data. The model structure of database management system and the function of level two image ensure that the data has high physical independence and logical independence.

Pattern: A description of the logical structure and characteristics of all data in a database

External mode: Local logical structure of data, usually a subset of patterns

Internal mode: Also known as storage mode, is the representation of data within the database system, that is, the physical structure of the data and the description of the storage mode.

Data definition language: DDL, which defines the language of the database schema, the outer mode, the internal schema

Database manipulation Language: DML, a statement used to query, insert, delete, and modify data in a database

Logical independence of data and programs: when the pattern changes (such as adding new relationships, changing attributes), the database administrator changes the image of the external mode/pattern, leaving the external mode unchanged.

Physical independence of data and programs: when the storage structure of a database changes, the schema/internal mode image is changed by the database administrator, so that the pattern remains unchanged so that the application does not have to change.

Cartesian product: A popular point is a collection of two combinations of two elements that are taken out of a set

Base table: The base table is a table that exists independently of itself, and a relationship in SQL corresponds to a table

View: A table that is exported from one or several base tables, and the view itself is not stored independently in the database and is a virtual table. If the view's properties come from a collection function, an expression, the view must not be updated.

Trigger: Is the method that the database administrator on SQL Sever to ensure data integrity

Index: Created on a database table to improve the level of query on the data in the table. Syntax: Action (like Drop) index index name on table name

Normalization of Judgment:

1. Second normal form (2NF): The property is completely dependent on the primary key

2.3NF: property is not dependent on other non-primary properties

3. BCNF: There is a case where the key field determines the key field, which does not conform to the BCNF paradigm

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The explanation of the relevant noun in the introduction of database system