机械外文翻译文献翻译数据库管理系统

机械外文翻译文献翻译数据库管理系统内容摘要：

, phone number, and age, were now considered to belong to that person instead of being extraneous data. This allows for relationships between data to be relation to objects and their attributes and not to individual fields. 机械专业中英文文献翻译 Another big game changer for databases in the 1980s was the focus on increasing reliability and access speeds. In 1989, two professors from the University of Michigan at Madison, published an article at an ACM associated conference outlining their methods on increasing database performance. The idea was to replicate specific important, and often queried information, and store it in a smaller temporary database that linked these key features back to the main database. This meant that a query could search the smaller database much quicker, rather than search the entire dataset. This eventually leads to the practice of indexing, which is used by almost every operating system from Windows to the system that operates Apple iPod devices. 4. DBMS building blocks A DBMS includes four main parts: modeling language, data structure, database query language, and transaction mechanisms: Components of DBMS DBMS Engine accepts logical request from the various other DBMS subsystems, converts them into physical equivalents, and actually accesses the database and data dictionary as they exist on a storage device. Data Definition Subsystem helps user to create and maintain the data dictionary and define the structure of the files in a database. Data Manipulation Subsystem helps user to add, change, and delete information in a database and query it for valuable information. Software tools within the data manipulation subsystem are most often the primary interface between user and the information contained in a database. It allows user to specify its logical information requirements. Application Generation Subsystem contains facilities to help users to develop transactionintensive applications. It usually requires that user perform a detailed series of tasks to process a transaction. It facilitates easytouse data entry screens, programming languages, and interfaces. Data Administration Subsystem helps users to manage the overall database environment by providing facilities for backup and recovery, security management, query optimization, concurrency control, and change management. Modeling language A data modeling language to define the schema of each database hosted in the DBMS, according to the DBMS database model. The four most mon types of models are the: •hierarchical model, •work model, •relational model, and •object model. Inverted lists and other methods are also used. A given database management system may provide one or more of the four models. The optimal structure depends on the natural anization 机械专业中英文文献翻译 of the application39。 s data, and on the application39。 s requirements (which include transaction rate (speed), reliability, maintainability, scalability, and cost). The dominant model in use today is the ad hoc one embedded in SQL, despite the objections of purists who believe this model is a corruption of the relational model, since it violates several of its fundamental principles for the sake of practicality and performance. Many DBMSs also support the Open Database Connectivity API that supports a standard way for programmers to access the DBMS. Before the database management approach, anizations relied on file processing systems to anize, store, and process data files. End users became aggravated with file processing because data is stored in many different files and each anized in a different way. Each file was specialized to be used with a specific application. Needless to say, file processing was bulky, costly and nonflexible when it came to supplying needed data accurately and promptly. Data redundancy is an issue with the file processing system because the independent data files produce duplicate data so when updates were needed each separate file would need to be updated. Another issue is the lack of data integration. The data is dependent on other data to anize and store it. Lastly, there was not any consistency or standardization of the data in a file processing system which makes maintenance difficult. For all these reasons, the database management approach was produced. Database management systems (DBMS) are designed to use one of five database structures to provide simplistic access to information stored in databases. The five database structures are hierarchical, work, relational, multidimensional and objectoriented models. The hierarchical structure was used in early mainframe DBMS. Records’ relationships form a treelike model. This structure is simple but nonflexible because the relationship is confined to a onetomany relationship. IBM’s IMS system and the RDM Mobile are examples of a hierarchical database system with multiple hierarchies over the same data. RDM Mobile is a newly designed embedded database for a mobile puter system. The hierarchical structure is used primary today for storing geographic information and file systems. The work structure consists of more plex relationships. Unlike the hierarchical structure, it can relate to many records and accesses them by following one of several paths. In other words, this structure allows for manytomany relationships. The relational structure is the most monly used today. It is used by mainframe, midrange and microputer systems. It uses twodimensional rows and columns to store data. The tables of records can be connected by mon key values. While working for IBM, . Codd designed this structure in 1970. The model is not easy for the end user to run queries with because it may require a plex bination of many tables. The multidimensional structure is similar to the relational model. The dimensions of the cube looking mo。