数据库原理基本概念Basic concepts of database theory一、数据---DataData is everything.Data can exist in a variety of forms -- as digital numbers, text, image, sound, video and etc.二、数据库---DatabaseA database is a repository for a collection of computerized data files.A database is an organized collection of data for one or more purposes, usually in digital form. The data are typically organized to model relevant aspects of reality (for example, the availability of rooms in hotels), in a way that supports processes requiring this information (for example, finding a hotel with vacancies). The term "database" refers both to the way its users view it, and to the logical and physical materialization of its data, content, in files, computer memory, and computer data storage.三、数据库系统---DBS(Database System)A database system is a term that is typically used to encapsulate the constructs of a data model, database Management system (DBMS) and database.四、数据库管理系统---DBMS(Database ManagementSystem)A database management system (DBMS) is a software package with computer programs that control the creation, maintenance, and the use of a database. It allows organizations to conveniently develop databases for various applications by database administrators (DBAs) and other specialists.A collection of programs that enables you to store, modify, and extract information from a database.五、数据库管理员---DBA(Database Administrator)A database administrator is a person responsible for the design, implementation, maintenance and repair of an organization's database.六、模式---SchemaA database schema of a database system is its structure described in a formal language supported by the database management system (DBMS) and refers to the organization of data to create a blueprint of how a database will be constructed.In other words, schema is the structure of the database that defines the objects in the database.七、内模式---Internal SchemaInternal Schema: storage schema– Describes how data is stored and what the physical structureof data is.– Totally dependent on particular implementation.– There is only one internal schema in a DB.八、外模式---External SchemaExternal Schema: user schema or subschema– Interface between users and DBS– Describes the logical structure of some local data oriented tosome applications and users– There may be many external schemata in a DB.九、三级模式---Three Levels of Schema-Physical level: describes how a record (e.g., customer) is stored.-Logical level: describes data stored in database, and therelationships among the data.-View level: application programs hide details of data types. Views can also hide information (such as an e mployee’s salary)for security purposes.十、映像---MappingData mapping is the process of creating data element mappings between two distinct data models. Data mapping is used as a first step for a wide variety of data integration tasks including:●Data transformation or data mediation between a data source anda destination●Identification of data relationships as part of data lineageanalysis●Discovery of hidden sensitive data such as the last four digitssocial security number hidden in another user id as part of a datamasking or de-identification project●Consolidation of multiple databases into a single data base andidentifying redundant columns of data for consolidation orelimination十一、逻辑独立性---Logical Independence When schema changes (e.g., new relation/new attribute added), DBA changes the Ex-schema/schema mapping, so the external schema can stay unchanged, i.e. applications needn’t be changed.十二、物理独立性---Physical Independence When internal schema changes ，DBA changes the schema/internal schema mapping, so the schema can stay unchanged . Thus, the external schema also keeps the same.十三、数据模型---Data ModelA data model in software engineering is an abstract model, that documents and organizes the business data for communication between team members and is used as a plan for developing applications, specifically how data is stored and accessed.A data model can be sometimes referred to as a data structure, especially in the context of programming languages. Data models are often complemented by function models, especially in the context of enterprise models.。