外文文獻翻譯數(shù)據(jù)庫_外文翻譯中英文對照(編輯修改稿)
2025-01-09 04:21 本頁面
【文章內(nèi)容簡介】 tion that specifies the operation and the describedrecord or bination of records. A query optimizer translates the description into aprocedure to perform the database Model The work model creates relationships among data through a linkedliststructure in which subordinate records can be linked to more than one parent approach bines records with links which are called pointers. The pointersare addresses that indicate the location of a record. With the work approach asubordinate record can be linked to a key record and at the same time itself be a keyrecord linked to other sets of subordinate records. The work mode historically hashad a performance advantage over other database models. Today such performancecharacteristics are only important in highvolume highspeed transaction processingsuch as automatic teller machine works or airline reservation system. Both hierarchical and work databases are application specific. If a newapplication is developed maintaining the consistency of databases in differentapplications can be very difficult. For example suppose a new pension application isdeveloped .The data are the same but a new database must be Model The newest approach to database management uses an object model in whichrecords are represented by entities called objects that can both store data and providemethods or procedures to perform specific tasks. The query language used for the object model is the same objectorientedprogramming language used to develop the database application .This can createproblems because there is no simple uniform query language such as SQL . Theobject model is relatively new and only a few examples of objectoriented databaseexist. It has attracted attention because developers who choose an objectorientedprogramming language want a database based on an objectoriented Database Similarly a distributed database is one in which different parts of the databasereside on physically separated puters . One goal of distributed databases is theaccess of information without regard to where the data might be stored. Keeping inmind that once the users and their data are separated the munication andworking concepts e into play . Distributed databases require software that resides partially in the largerputer. This software bridges the gap between personal and large puters andresolves the problems of inpatible data formats. Ideally it would make themainframe databases appear to be large libraries of information with most of theprocessing acplished on the personal puter. A drawback to some distributed systems is that they are often based on what iscalled a mainframeentire model in which the larger host puter is seen as thema
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