【正文】 外文資料原文 Database Systems1. Introduction to Database System Today more than at any previous time the success of ananization depends on its ability to acquire accurate and timely dataabout its operation to manage this data effectively and to use it toanalyze and guide its activities. Phrases such as the informationsuperhighway have bee ubiquitous and information processing is arapidly growing multibillion dollar industry. The amount of information available to us is literally exploding andthe value of data as an anizational asset is being widely paradox drives the need for increasingly powerful and flexible datamanagement systems. A database is a collection of data typically describing the activitiesof one or more related anizations. For example a university databasemight contain information about the following. ●Entities such as students faculty courses and classrooms. ●Relationships between entities such as students’ enrollment incourses faculty teaching courses and the use of rooms for courses. A database management system or DBMS is software designed toassist in maintaining and utilizing large collections of data and the needfor such systems as well as their use is growing rapidly. The alternativeto using a DBMS is to use ad hoc approaches that do not carry over fromone 9 application to another for example to store the data in files and writeapplicationspecific code to manage it. The area of database management systems is a microcosm ofputer science in general. The issues addressed and the techniquesused span a wide spectrum including languages objectorientation andother programming paradigms pilation operating systemsconcurrent programming data structures algorithms theory paralleland distributed systems user interfaces expert systems and artificialintelligence statistical techniques and dynamic programming . Database management continues to gain importance as more andmore data is brought online and made ever more accessible throughputer working. Today the field is being driven by exciting visionssuch as multimedia databases interactive video digital libraries and ahost of scientific projects such as the human genome mapping effort andNASA’s Earth Observation System project and the desire of paniesto consolidate their decisionmaking processes and mine their datarepositories for useful information about their business. Commerciallydatabase management systems represent one of the largest and mostvigorous market segments. Thus the study of database systems couldprove to be richly rewarding in more ways than . Database consists A database consists of a file or a set of files. The information in thesefiles may be broken down into records each of which consists of one ormore fields. Fields are the basic units of data storage and each fieldtypically contains information pertaining to one aspect or attribute of theentity described by the database. Using keywords and various sortingmands users can rapidly search rearrange group and select thefields in many records to retrieve or create reports on particularaggregates of data. Database records and files must be anized to allow retrieval of theinformation. Early systems were arranged sequentially numerically or chronologically the development ofdirectaccess storage devices made possible random access to data viaindexes. Queries are the main way users retrieve database the user provides a string of characters and the putersearches the database for a corresponding sequence and provides thesource materials in which those characters appear. A user can request forexample all records in which the content of the field for a person’s lastname is the word Smith. In flat databases records are anized according to a simple list ofentities many simple databases for personal puters are flat instructure. The records in hierarchical databases are anized in a treelikestructure with each level of records branching off into a set of smallercategories. Unlike hierarchical databases which provide single linksbetween sets of records at different levels work databases createmultiple linkages between sets by placing 10 links or pointers to one set ofrecords in another the speed and versatility of work databases haveled to their wide use in business. Relational databases are used where assoc