Database and Data Model

Database TechnologyGenerally includes Data ManagementAnd Data Processinga database system is essentially a system that uses a computer to store data. Basic Concepts: Data->datais the base object stored in the database (text This, graphics, images, audio, video, etc. are data） ：data is a symbol that describes things. of the datainterpretation is a description of the data deduction, the meaning of the data becomes the semantics of the data . Database-database/dbThe warehouse database that holds the data is a collection of large amounts of data that are stored on the computer for long periods of time and are organized and shareable. Features of the database:permanent storage, organized, shareable database management system->database Management System/dbmsis a system software dedicated to the management and maintenance of data database system->database System/dbsThe system after the introduction of the database by the computer, generally byDatabase , database management system, application, database administrator. database administrator->database administrator/dbaUsually: make the database system a databasedisk, DBMS, DB, Application the development of data management technologyMain: file Management and database management Data Independence applications do not rely on any specific physical representations and access techniques, including: Physical independence and logical independence Physical Independence : When the storage location or structure of the data changes, it does not affect the characteristics of the program. Logical Independence： when the information content of the real world changes, such as increasing, deleting, etc., does not affect the characteristics of the application。 Data and Information Data: A symbol record describing a thing Information: Get meaningful content from your data Grammar: The format of the data specifies Semantics: What the data means data is a form of information that can be useful only through interpretation or processing .characteristics of data in a database:1: Static Characteristics: including The basic structure of data, the relation between data, and the restriction of data value range2: Dynamic Features: Refers to the actions and rules that can be performed on the data. （ Query, change ( Insert, delete, update )) Data Model three elements : In general, the static characteristics of the data and dynamic characteristics of the description. That is, to describe the data include：The basic structure of the data, constraints on the data, and actions defined on the data. Data ModelData Model ( Data Model）is the abstraction of the characteristics of the real world data. The data model is used in the database to abstract, represent, and process data and information in the real world. The data model meets 3 requirements: 1: Can realistically simulate the real World 2: Easy to understand 3: can be easily implemented on the computerModel:1: conceptual Layer Data Model2: organization-level data model/data ModelInclude: hierarchical model, mesh model, relational model, object-relational model hierarchy Model: tree-structured mesh model: graphical structure Relational Data Model :is the most important data model at present. The relational data model is derived from mathematics, which sees data asThe elements in a two-dimensional table, and this two-dimensional table is called a relationship in a relational database. A model that represents a relationship between entities and entities is called arelational data model. Oracle,access,microsoft SQL Serverand all that.Relationship-based database management system。The most fundamental difference between the relational data Model and the tomographic model and the mesh model ：The relational data model adopts the non-navigational data access method, and the data structure change does not affect the access to the information. Entity-Contact Model: (Conceptual layer) entities: (entity) A collection of real-world objects that have a common nature and can be distinguished, or objects that have the same structure. (Staff, students, teachers) Property: Attribute A data item that describes the nature or characteristics of an entity or contact, and all instances that belong to an entity have the same pay propertyIdentity attribute/entity code for an entity: a property that uniquely identifies an entity or a minimum set of properties. Contact: Relationship connection is the correlation between data, and it is an objective application statement chain. Intra-entity linkages。 A connection between an entity's internal attributes. the linkages between entities。 The relationships between different entity attributes. Contact:One-to-one contact, one-to-many links, many-to-many links . Database structure: level Three mode, level two mappingBasic concepts of the pattern: Data Model: Describe the organization of data Mode: The specific data is described using the given data model. A schema is a description of the logical structure and characteristics of all data in a database, In effect, it corresponds to the table header of the relational table. a specific value of a pattern is called an instance of a pattern. Pattern is equivalent to a two-D table header, each row in a two-dimensional table is equivalent to an instance of the pattern. Three-level mode structure: external mode, mode, and internal mode of the database1: External modeExternal mode/user mode/Sub-mode, it's content from Pattern。 The outer mode is usually a subset of patterns, and a database can have multipleExternal mode. The external model is also a measure to ensure the security of the database. External mode is also Relationship of, or close to the relationship.2: ModeMode/logic Mode/Conceptual mode: It is the contempt of the logical structure and feature of all data in the database, it is the public view of all users and the middle layer of database structure. Patterns are composed of values of many concept record types. A pattern is actually a view of the database data on a logical level, a database only oneMode. The schema in the relational database must be Relationship of。3: Internal modeInternal Mode/ Storage Mode。 The inner mode is not the same as the physical layer. Internal mode It's not a relationship., which is how the data is physically stored. In fact relationship model independent of internal mode。schema image and data independenceExternal mode/mode Image: Separate application and DB for logical Independence . mode/Internal mode image: Separate application and DB for physical independence . So that database applications do not change with the logical or storage structure of the database data.

Database and Data Model