The first chapter Database System Overview
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The basic concept of the first database
First, the basic concepts of database
(1) Data: records of a transaction descriptor means, authentication information can be recorded with a physical symbol.
(2), the database: organized in a computer, the long-term storage can be shared data set, wherein the data is organized according to a certain data model, and shared described, having a smaller redundancy, higher data independence , easy to expand and can be shared by users. (Referred to as stored data warehouse)
1, data stored in the database has three characteristics:
永久存储、有组织、可共享.
(3), database management systems: dedicated to establishing and managing a set of database software, between applications and operating systems.
Function of the database management system comprising:
(1), data definition function
(2), data manipulation functions
(3), operation and management functions of the database
(4), the establishment and maintenance of database functions:创建数据库及对数据库空间的维护、数据库的备份与恢复功能、数据库的重组织功能和性能监视、分析.
(5), data organization, storage and management functions: index lookup, sequential search
(6), the other functions: a network communication function and other software, data transfer between different database management systems)
(4), the database system: refers to the system after the introduction of computer database technology. Generally complete database system: databases, database management systems and related utilities, applications, database administrators and users.
Data management technology development Section II
First, the database design goals
(1), manual management stage, the data management features of this stage are as follows:
1, the data is not saved
2, application management dataThe logical structure, physical structure, a method of accessing design work done by writers.
3, the data for the application
A set of data corresponding to only one program. There are a lot of redundant data between programs and procedures, independence of the data is poor.
(2), the file system phase, separating the logical and physical structure of the data, the mapping between the logical structure and physical structure implemented by the storage method. Data can be stored for a long and specialized management features, provides physical data independence, file-level data sharing.
(3), the database system stage, has the following characteristics
1, data integration
数据的集成是数据库管理系统的主要目的。2, data sharing high
3, small redundant data
4, data consistency
5, high data independence
6, unified management and control1), data security is the protection of data
2), the correctness of the data integrity, validity and compatibility
3),并发控制是指当多个用户的并发进程同时存取、修改数据库时，出现错误，因而对多用户的并发操作加以控制和协调。
4), recovery, database recovery from the error state to have a certain function known correct state.
7, reduce the workload of application development and maintenance
Section III database system structure
A tertiary structure model database system
Three architectures: user-level, conceptual level, the physical level
three mode configuration database system refers to a database system is composed of模式、外模式和内模式。
(1), mode ( 称为概念模式或逻辑模式public view, a conceptual view, a database is only one pattern.)
Schema defines the logical data links between data, data related to security and integrity.
Description external database provides data to the user mode, as described in the data storage mode, while the mode is the intermediate layer between the two.
(2), an outer pattern ( 称为子模式或用户模式user view)
an outer view of the pattern is used to meet the needs of different users of the database, a subset of model, the overall data structure is a database of local reconstruction.
(3), the pattern ( 称为存储模式of the physical structure description data in the database and the storage mode, is a representation of the data within the database. A database is only one inner pattern)
(4), two mapping data independence three modes of the structure
1, three mode three mode configuration of database system are three data abstraction, has the following characteristics:
1), and describes the logical structure of a database of characteristics (conceptual schema) is described independently of the other database hierarchy (in / out mode), and is the critical core design database.
2), an internal storage pattern dependent on a conceptual model of the database, but independent of external storage mode mode, independent of the specific storage device.
3), the logical structure of the user (external mode) is defined on the basis of the results described in the global logic, for particular applications, independently of the mode and internal storage devices.
4), a specific application is written on the logical structure of the outer pattern, depending on the particular outer pattern, the pattern and structure of the database stored independently.
2, two images
1), an outer pattern / mode map
Defines the mapping relationship between the conceptual model and the respective outer pattern, the outer mode is described.
2), mode / the mode map,
是唯一的。It defines the correspondence relationship between the logical structure and physical global database stored in the mode described.
Second, the operation and structure of the database application system
(1), client / server architecture (Clinet / Sever, C / S)
(2), the browser / server architecture (Browser / Sever, B / S )
Section IV Data Model
A data characteristic constituent elements of the data model
The data model is used to describe a set of concepts and defining constraints between the data structure definition operations and data on a structure. ( 数据模型通常由数据结构、数据操作和数据约束三要素组成)
(1), data structure (a basic characteristic reaction data model)
Data structure describes the static characteristics of the system, i.e., the type of data link between the data object, content, attributes, and data objects.
(2), data manipulation
Describes a dynamic data manipulation features of the system, examples of various objects is allowed to execute a set of operations, including operations and rules relating to operation. There are two types of data retrieval and update operations.
(3), data constraint 数据完整性约束、安全性约束以及并发控制约束( )
The syntax and semantics of the associated data between the data structure description data constraints, including constraints and dependencies, and each dynamic change rule data, in order to ensure the accuracy, effectiveness and compatibility data.
Second, the classification of the data model
(1), conceptual data model layer
The concept of data abstraction layer is the top level, its purpose is to model the world according to the user's point of view. Conceptual data model layer, also called information model or conceptual model
1, the basic concept of information in the world
1), entities: the objective existence of things can be distinguished from each other entities called.
2), Attribute: entity having a certain characteristic attributes of the entity referred to.
3), the code or key:可唯一标识实体的属性集称为码或键
4), domains: the range of the attribute property called domains.
5), an entity type: an entity having the same attribute must have common characteristics and properties. (The name of the entity names and attributes constituting the set of entity type)
6) entity set:同型实体的集合称为实体集。
7), contact: internal contact entity generally refers to various properties of the link between the entities.
2, the conceptual model of representation
Entity - Contact with ER diagram, also referred to as methods or ER ER model
entity type is represented by a rectangle
attribute, represented by oval
links, represented by diamonds
(2), the logical data model layer 数据的逻辑模型( )
Logical data abstraction layer intermediate layer, the overall logical structure description data.
Logical data model: hierarchical model, the mesh model, the relational model, the object-oriented model
1, the hierarchical model
features: one and only one node has no parent, and the other node has only one parent node.
2, a mesh model
3, the relational model
relational model with two-dimensional table structure to represent the model and physical links between entities and tables in the form of a two-dimensional tissue data in the database.Relational model has the following advantages:
1), the relational model is based on rigorous mathematical concepts on.
2), the relational model concept of a single, unified to represent the links between entities and entity relationship with, data retrieval and update the results is also used to represent the relationship, its simple, clear, easy to understand user, easy to use.
3), the relationship between the access route model transparent to the user, data independence higher, better security and confidentiality, to simplify part of the work.4, object-oriented model
object-oriented model is a conceptual model is a logical model
(3), the physical layer data model (referred to as physical data model)
Each logic model are implemented at the physical model corresponds thereto. Physical model database abstract bottom, determines the physical data storage structure, data access path and adjust and optimize the performance of the database.
Physical model design goals: to improve database performance and efficient use of storage space.
