Introduction to Database System study notes (i)
Time: First week Grade: Junior Students: Nantong University network engineering He Tiseng
2017.9.14
I. INTRODUCTION
1.1 Database System Overview
1. Data
Symbolic records describing things are called data. The meaning of the data is called the semantics of the data, and the data is not divided with its semantics. For example, 93 is a data, he can be a student's grade, can also be his weight, but also may be a class number.
2. Database
The database is the repository where the data is stored. Strictly speaking, data is a collection of large amounts of data stored in a computer, organized, and shareable over a long period of time. The data in the database is organized, described and stored in a certain data model, with smaller Sanyudo (redundancy), high data independency and Extensibility (scalability), and sharing for various users.
The database has three basic features: permanent storage, organized and shareable.
Redundancy is also known as affluence, that is, from a security perspective to consider the excess of a quantity, which is to ensure that the instrument, equipment or a work under normal conditions can also operate normally.
Data independence means that the application and data structures are independent from each other and are not affected. Data independence includes data logical independence and data physical independence.
Extensibility is the degree to which you can upgrade, and the more scalable you are, the more space you will have to upgrade.
3. Database management System
The database management system is a layer of data management software located between the user and the operating system. The database management system and the operating system are the basic software of the computer.
His main functions are as follows:
1. data definition :DBMS provides data definition language DDL (Language) for user-defined database Three-level schema structure, Two-level images and constraints such as integrity constraints and confidentiality restrictions. DDL is mainly used to establish and modify the database structure. The library structure described by DDL only gives the framework of the database , and the framework information of the database is stored in the data Dictionary.
2. Data manipulation: DBMS provides data manipulation language DML (manipulation Language) for users to implement data append, delete, update, query and other operations. 3. Database operation Management: Database operation management function is DBMS's operation control, management function, including concurrency control in multiuser environment, security check and access limit control, integrity check and execution, organization management of running log, transaction management and automatic recovery, that is to guarantee the atomicity of transaction. These functions ensure the normal operation of the database system. 4. Data organization, storage and management: DBMS to classify and organize, store and manage various kinds of data, including data dictionary, user data, access path and so on, need to determine what file structure and access way to organize the data at the storage level, how to realize the connection between data. The basic goal of data organization and storage is to improve storage space utilization and choose appropriate access method to improve access efficiency. 5. Database protection: Data in the database is the strategic resource of the information society, so the protection of data is of paramount importance. The DBMS protects the database through 4 aspects: Database recovery, database concurrency control, database integrity control, database security control. Other protection functions of DBMS include the management of system buffers and some adaptive regulation mechanism of data storage. 6. Maintenance of the database: This section includes data loading, conversion, dump of database, reconfiguration of database and performance monitoring functions, which are completed by various use programs respectively. 7. Communication: DBMS with the operating system online processing, time-sharing system and remote job input related interface, responsible for processing data transmission. The database system in the network environment should also include the communication function between DBMS and other software systems in the network, and the interoperability function between the databases. 4. Database System
The database system is made up of a database, a database management system and its application development tools, Applications (application) and database administrators (databases Administrator) are systems that store, manage, process, and maintain data. DBS includes DB, DBMS, DBA, APP. 5. Development of data management technologyhuman management stage → file system stage → database system phase. 1.2 Data Model Data Model is also a model, he is the real world data characteristics of the abstract, is the real world simulation. Data model is the core and foundation of database system. 1. Class two data ModelThe data model should meet three requirements: one is to be able to realistically simulate the real world, the second is easy to understand, third is easy to implement on the computer. The data model is divided into two categories based on the different purposes of the application: the first is the conceptual model (conceptual model) and the second is the logical model and the physical model. Conceptual Model: modeling data and information according to the user's point of view, primarily for database design. (not suitable for computers)logical Model: mainly includes the hierarchical model (hierarchical models), the network model, the relational model (relational model), the face object data model Model) and the object-relational data models (object relational, semistructured data model), and so on, he modeled the data according to the computer system's point of view, mainly used in the database management system implementation. hierarchical model refers to the use of a "tree-oriented" data structure to represent various entities and relationships between entities, each node in the tree represents a record type, the tree structure represents the relationship between entities. Hierarchical model is the first data model used in commodity database management system. advantages: The relationship between records is implemented by pointers, and the query efficiency is high.
disadvantage: Can only represent 1:n relationship, because the hierarchical order of tree structure is strict and complex, the query and update operation of data is more complicated, so it is very complicated to write the program. Mesh Model:the model of the relationship between entity type and physical body is represented by network structure. As the name implies, one thing is connected to the other, which makes up a network diagram. A mesh model is a database model that can flexibly describe things and their relationships. First invented by the American Charles Bachman. advantages: The relationship between records is implemented by pointers, and the query efficiency is high; a m:n connection can also be achieved by splitting it into two 1:n connections. Cons: Writing a program is complicated, and programmers must be familiar with the logical structure of the database. Relational Model: a relationship is actually the state or content of a relationship pattern at a certain point in time. That is, the relationship pattern is type, and the relationship is its value. Relational patterns are static and stable, and relationships are dynamic, changing over time, as relational operations constantly update data in the database. In practice, however, relationship patterns and systems are often called relationships, and readers can distinguish them from context. The biggest difference between the relational model and the hierarchical model and the mesh model is that the keywords are used instead of the pointers to retrieve the data, the tables are easy to understand and the SQL language is widely used as the standardized language of the relational database. Typical relational database products are DB2, ORACLE, SYBASE, INFORMIX, Access. 2.in order to abstract and organize the concrete things in the real world into a data model supported by a database management system, people often first abstract the real world into the information world and then transform the information world into the machine world. Real world → information World → machine worldSeven. Database design7.1 Introduction to Database designdatabase design is to construct (design) optimized database logical mode and physical structure for a given application environment, and to establish database and its application system, so that it can effectively store and manage data, satisfy various users ' application requirements, including information management requirements and data operation requirements. Information Management requirements: what data objects should be stored and managed in the database. Data operational requirements refer to what needs to be done on the data object, such as querying, adding, deleting, changing, and counting. The goal of data design is to provide an information infrastructure and an efficient operating environment for users and various application systems. Efficient operating environment refers to the efficiency of database data access, database storage space utilization, database system operation and management efficiency, etc. are high. features of 7.1.1 database designThree-point technology, seven-point management, more than basic data. More than basic data emphasizes that the collection, collation, organization and updating of data is an important link in database construction. structure (data) design and behavior (processing) design. Database design should be combined with application system design. That is to say the whole design process to the database structure design and data processing design close together. Basic steps of 7.1.3 database design6 StagesDemand AnalysisConceptual Structure AnalysisLogical Structure AnalysisPhysical Structure AnalysisDatabase Implementationdatabase operation and MaintenanceIn the design process, requirements analysis and conceptual structure design can be independent of any database management system (not related to the programmer ....) ), logical structure design and physical structure design are closely related to the selected database management system.
Introduction to Database System study notes (i)
