Databases for the average person to say
can be simply understood as a fixed format of data ***,
specifically for the solution of a certain type of data preservation and computation problems and the existence of the
like a unit of a variety of reports and documents,
only the software will help you to save and manage these documents and reports on the computer
help you calculate sums and other operations to generate a variety of data reports you want.
It's just that the software will help you save and manage these documents and reports on your computer,
helping you to calculate sums and so on, generating all the data you want to report.
Utilizing database software and the high-speed nature of computers,
you can greatly improve efficiency and correctness.
Reduce the cost of working time and labor.
Without them can be, but you have to deal with the data manually,
regardless of the amount of data is the same.
2. Overview and History of Database DevelopmentThe data model is the core and foundation of a database system. Therefore, the stage of development of database technology should be divided into the evolution of the data model as the main basis and sign. In general, database technology from the beginning to the present a **** experienced three stages of development: the first generation is a mesh, hierarchical database system, the second generation is a relational database system, the third generation is an object-oriented data model as the main feature of the database system.
The first generation includes mesh and hierarchical database systems, because although their data models are hierarchical and mesh models, but in essence the hierarchical model is just a special case of the mesh model. Both are formatted data models, both researched and developed in the late 60's, whether it is the architecture, database language, or data storage management, all have the *** same characteristics, so they should be divided into a generation.
The second generation of database systems supports the relational data model. The relational model not only has the advantages of simplicity and clarity, but also has relational algebra as a language model and relational data theory as a theoretical foundation. Therefore, the relational database has a good formal basis, strong data independence, database language nonprocedural and other characteristics, these characteristics are database technology has developed to the second generation of the significant signs. Although the relational data model describes the structure of real-world data and some important interconnections, it is still insufficient to capture and express the rich and important semantics of data objects, and thus it belongs to the syntactic model.
The third generation of database systems is characterized by richer data models, more powerful data management capabilities, and the ability to support new application requirements that are difficult to support with traditional databases.
(a) Features
The database management system will have a certain structure of data to form a ***, it mainly has the following characteristics:
1. data structure The data in the database is not disorganized, irrelevant, they have a certain organizational structure, belonging to the same *** of the data has similar characteristics.
2. data *** enjoyment between the various departments of a unit, there is a lot of duplication of information. The purpose of using a database is to unify the management of this information, reduce redundancy, so that each department *** enjoy the same data.
3. Independence of data Independence of data refers to the independence between data records and data management software. The data and its structure should be independent and should not go to change the application program.
4. Data Integrity Data integrity is the assurance that the data in the database is correct. There are many reasons that may cause data to be incorrect, and the database management system manages them by checking the nature of the data.
5. Data Flexibility A database management system is not a simple stack of data, it has many management functions based on recording data information, such as input, output, query, edit and modify.
6. Data security According to the responsibilities of the user, different levels of people have different rights to the database, the database management system should ensure the security of the data.
(ii) Functions
A good database management system should have many functions, the most basic of which are the following three:
1. Data Definition The database management system provides the function of defining the type of data and the form in which the data is stored. The information in each field of each record is one data. As the information in the record is different, its data type should also be different. By defining data types, data integrity can be ensured to some extent. The simplest requirement is that the integrity rules should ensure that no data of text type can be stored in a field defined as a number.
2. Data manipulation Database management systems provide a variety of ways to manipulate data. For example, look up information in a table or perform complex lookups in several related tables or files; update the contents of a field or multiple records using the appropriate commands; perform statistics on the data with a single command, or even program using database management system tools to achieve more complex functionality.
3. Data control The database management system provides certain protections for the data, thus ensuring that when multiple users *** enjoy the data, only authorized users can view or modify the data.
3. History of the development of database management and its corresponding characteristicsDatabase management system (database management system) is a large-scale software to manipulate and manage databases, is used to create, use and maintain databases, referred to as dbms.
It is a unified management and control of databases in order to ensure database security and integrity. Users access the data in the database through dbms, and database administrators also maintain the database through dbms.
It provides a variety of features that enable multiple applications and users to create, modify, and query databases in different ways at the same time or at different times. It enables users to easily define and manipulate data, maintain data security and integrity, and perform concurrent control and recovery of databases with multiple users.
By function, the database management system can be roughly divided into six parts: (1) Schema Translation: provides the data definition language (ddl). The database schema written in it is translated into an internal representation.
The logical structure of the database, integrity constraints and physical storage structure saved in the internal data dictionary. Various data operations of the database (such as lookup, modification, insertion, and deletion) and the maintenance and management of the database are based on the database schema.
(2) application compilation: the application containing statements to access the database, compiled into a target program that can run under the support of dbms. (3) Interactive query: provides easy-to-use interactive query language, such as sql.
dbms is responsible for executing query commands and displaying query results on the screen. (4) data organization and access: provides the physical organization of data on peripheral storage devices and access methods.
(5) transaction operation management: to provide transaction operation management and operation logs, security monitoring and data integrity checking of transaction operation, concurrency control of transactions and system recovery and other functions. (6) database maintenance: provide software support for database administrators, including data security control, integrity assurance, database backup, database reorganization and performance monitoring and other maintenance tools.
Relational model-based database management system has been perfected, and has been widely used in various industries as commercialized software. It is used in a distributed multi-user environment with a variety of server structures, which further extends the application of database systems.
With the advancement of new data models and data management implementation techniques, it can be expected that the performance of the dbms software will be updated and improved, and the application areas will be further broadened. It provides the following functions: (1) data definition function.
DBMS provides the appropriate data language to define (DDL) database structure, they are portrayed in the database framework, and is saved in the data dictionary. (2) Data access functions.
DBMS provides a data manipulation language (DML) to realize the basic access operations on database data: retrieval, insertion, modification and deletion. (3) database operation and management functions.
DBMS provides data control functions, that is, data security, integrity and concurrency control, etc. to effectively control and manage the database operation to ensure that the data is correct and valid. (4) database creation and maintenance functions.
Including the initial database data loading, database dumping, recovery, re-organization, system performance monitoring, analysis and other functions. (5) database transmission.
DBMS provides processing data transfer, the realization of the user program and the DBMS communication between the user program, usually with the operating system to coordinate the completion. Famous database management systems MS SQL SYBASE DB2 ORACLE MySQL ACCESS VF Common database management systems There are many database products, such as Oracle, Sybase, Informix, Microsoft SQL Server, Microsoft Access, Visual FoxPro and other products each with their own unique features, in the database market to occupy a place.
The following is a brief introduction to several commonly used database management systems. Oracle Oracle is one of the earliest commercialized relational database management system, is also widely used, powerful database management system.
Oracle as a general database management system, not only has a complete data management functions, or a distributed database system, support for a variety of distributed functions, especially to support Inter applications. As an application development environment, Oracle provides a set of interface friendly, full-featured database development tools.
Oracle uses the PL/SQL language to perform a variety of operations with openness, portability, scalability, and other features. Especially in Oracle 8i, it supports object-oriented features such as support for classes, methods, and attributes, making Oracle products an object/relational database management system.
Microsoft SQL Server Microsoft SQL Server is a typical relational database management system that runs on many operating systems, and it uses the Transact-SQL language to accomplish data operations. Because Microsoft SQL Server is an open system, other systems can interact with it perfectly.
The latest version of the product is Microsoft SQL Server 2000, which is characterized by reliability, scalability, availability, and manageability, and provides users with a complete database solution. Microsoft Office As one of the Microsoft Office components, Microsoft Access is a very popular desktop database management system in the Windows environment.
Using Microsoft Access does not require writing any code, just through the intuitive visualization of the operation can be completed most of the data management tasks. A Microsoft Access database includes many of the basic elements that make up a database.
These elements are tables for storing information, forms for displaying human-computer interfaces, queries for effective data retrieval, reports for information output carriers, macros for improving application efficiency, powerful module tools, and so on. It can not only be connected to other databases through ODBC to achieve data exchange and **** enjoyment, but also with Word, Excel and other office software for data exchange and **** enjoyment, and through the object linking and embedding technology in the database embedded and linked to sound, images and other multimedia data.
Principles for selecting a database management system Selection of a database management system should be considered from the following aspects: (1) the ease of constructing a database. Need to analyze the database management system there is no paradigm requirements, that is, whether it is necessary to analyze the real world in accordance with the data model specified in the system, the establishment of the corresponding model; database management statements are in line with international standards, in line with international.
4. A brief history of the development of databasesThe use of computers has given rise to data management techniques as the volume of data processing grows.
The development of data management technology and computer hardware (mainly external memory) system software and the scope of computer applications are closely linked. The development of data management technology has gone through the following four stages: manual management stage, file system stage, database stage and advanced database technology stage.
The birth of data management database history can be traced back to fifty years ago, when data management is very simple. Data was processed through a large number of sorting, comparing and tabulating machines running millions of perforated cards, the results of which were printed out on paper or made into new perforated cards.
And data management is the physical storage and processing of all these perforated cards. However, the data management revolution was sparked in 1950 when a computer called the Univac I from Remington Rand Inc. introduced a tape drive that could input hundreds of records a second.
In 1956 IBM produced the first disk drive, the Model 305 RAMAC, which had 50 platters, each 2 feet in diameter, and could store 5MB of data.
The biggest advantage of using disks was that they could access data randomly, whereas perforated cards and tapes could only access data sequentially.1951: The Univac system used magnetic tape and perforated cards for data storage.
The germ of the database system appeared in the 1960s. At that time, computers began to be widely used for data management, and there was an increasing demand for *** enjoyment of data.
The traditional file system can not meet the needs of the people, can be unified management and *** enjoy the data of the database management system (DBMS) came into being. The data model is the core and foundation of the database system, a variety of DBMS software is based on some kind of data model.
So usually also in accordance with the characteristics of the data model will be divided into traditional database system mesh database, hierarchical database and relational database three categories. The earliest mesh DBMS, is the United States General Electric Company Bachman et al. developed in 1961 IDS (Integrated Data Store).
1964 General Electric Company (General ElectricCo.) Charles Bachman successfully developed the world's first mesh DBMS that is, the first database management system - Integrated Data Store (Integrated Data Store), laying the foundation for the first mesh DBMS. Store IDS), laid the foundation for mesh databases, and was widely distributed and used at the time. IDS has the characteristics of the data schema and logging, but it can only run on GE hosts, and the database has only one file, and all the tables of the database must be generated by hand coding.
Later, a GE customer, BF Goodrich Chemical, eventually had to rewrite the entire system, naming the rewritten system the Integrated Data Management System (IDMS). The mesh database model is a more natural analog for both hierarchical and non-hierarchical things, and before the advent of relational databases mesh DBMSs were more commonly used than hierarchical DBMSs.
Mesh databases occupy an important place in the history of database development. Hierarchical DBMS is followed by the emergence of networked databases, the most famous and typical hierarchical database system is the IBM company in 1968 developed IMS (Information Management System), a hierarchical database suitable for its mainframe.
This is the earliest large database system program product developed by IBM. Since its creation in the late 1960s, it has evolved to IMSV6, which provides support for advanced features such as clustering, N-way data ***sharing, and message queuing ***sharing.
This 30 year old database product is now playing a new role in today's WWW application connectivity, business intelligence applications, and in 1973 Cullinane (later Culli Software), began selling an improved version of Goodrich's IDMS and grew to become the largest software company in the world at the time.
Reticulated and hierarchical databases have solved the problem of centralization and ****-enjoyment of data very well, but there is still a big lack of data independence and level of abstraction. When users access these two databases, they still need to specify the storage structure of the data and point out the access path.
The later emergence of relational databases better solve these problems. 1970, IBM researcher Dr. E.F. Codd in the publication "munication of the ACM" published an article called "A Relational Model of Data for Large A Relational Model of Data for Large Shared Data Banks" in the journal munication of the ACM, Dr. E.F. Codd, a researcher at the University of California, Berkeley, introduced the concept of relational modeling and laid the theoretical foundations of relational models.
This paper is widely recognized as a landmark in the history of database systems, despite the fact that Childs had already proposed a ***-oriented model in 1968, and Codd's vision was to create a beautiful data model for databases.
Later, Codd published several articles on paradigm theory and the 12 criteria for measuring relational systems, laying the foundation for relational databases with mathematical theory. The relational model has a strict mathematical foundation, a relatively high level of abstraction, and is simple and clear to understand and use.
But at the time, there were also people who thought that the relational model was an idealized data model that was unrealistic to use to implement a DBMS, and were particularly concerned that the performance of relational databases would be unacceptable, and even more so that some people viewed it as a serious threat to the normalization of mesh databases, which was in progress at the time. To promote understanding of the issues, the ACM took the lead in organizing a symposium in 1974, where there was a debate between the pro- and anti-relational database factions, led by Codd and Bachman, respectively.
This famous debate drove the development of relational databases, which eventually became the mainstay of modern database products.
In 1969 Edgar F. "Ted" Codd invented the relational database.
After the relational model was established in 1970, IBM added more researchers to the San Jose labs to work on the project, which became known as System R. The goal was to demonstrate the feasibility of a full-featured relational DBMS.
The project ended in 1979 with the completion of the first DBMS to implement SQL. however, IBM's commitment to IMS prevented System R from going into production, and it was not until 1980 that System R was formally introduced to the market as a product.
Three reasons for IBM's slow pace of productization: IBM valued reputation, quality, and minimizing failures; and IBM was a .