英语翻译The relational model is a theoretical model of databases

英语翻译
The relational model is a theoretical model of databases because with it one can create sets of formulas that represent or model database systems.With such a model a database designer or researcher may study the properties of a database system without actually having to implement it.Having analysed database systems in theory it is then possible to come to conclusions as to what is the best way of achieving a good database design and what are the best ways of using the database.
Theoretical models abound in all branches of science.For instance,the economist may study how the economy of a country will behave,given certain conditions,by construction a system of definitions and formulas that model the behaviour of the economy.The astronomer may similarly model the behaviour of the solar system.The accuracy and reliability with which a theoretical model mimics the properties and behaviour of what which it attempts to model depend on the assumptions built into the model.If these assumptions are unrealistic or oversimplified the predictions and analyses made by using the model may be nive or unrealistic.For example,attempts by economists to predict the behaviour of the economy illustrate this problem.Different schools of economic thought will use models based on different and sometimes contradictory assumptions resulting in a wide range of advice on how to create a healthy economy.The quality of a theoretical model must ultimately be determined by how its analyses and predictions coincide with the actual behaviour of that which it models.The relational model must be judged on its ability to model accurately,and to predict the properties and behaviour of database systems.
The relational model has been criticized as being unrealistic and oversimplified in various respects.However,the relational model has been the major vehicle of database research for over a decade; it is the basis for many current DBMSs; and results from the theory of relational databases have found their way into many current computer system design methods.Though the relational model has many known imperfections,it was adopted by most databases researchers in the 1970s and 1980s as the best database model available.The search for something which is widely accepted as being better is still in progress.
The relational model is a particular type of theoretical model:it is a data model.A data model provides a means of representing data and relationships between data items.It also specifies the ways in which the data may be used.A data model will therefore include three parts:

关联模型是一个理论模型数据库,因为它可以制造套公式代表 或模型数据库系统.这种模型数据库设计者或研究者可能性能研究的一个数据库系统,而不真正具有 推行这项工作.在分析数据库系统,在理论上是可能的话,来作为结论,什么是最好的 方式实现了良好的数据库设计和什么是最好的方式,利用该数据库.理论模型比比皆是,在所有学科.比如,经济学家可以研究如何对一个国家的经济将表现,在一定条件下,建筑系统的定义和计算公式,模型经济行为的.天文学家的,可同样的模式,行为的太阳系.的准确性和可靠性提供了理论模型的火堆中的性能和行为究竟它试图 模型取决于假设建成模型.如果这些假设是不现实的或过于简单的预测和分析,利用该模型可以或nive 不现实的.例如,曾试图经济学家预测经济行为的说明这个问题.来自不同学校的经济思想将利用模型基于不同的,有时相互矛盾的假设产生了广泛 就如何创造一个健康的经济.质量的一个理论模型,最终必须取决于它如何分析和预测符合实际 行为,它的型号.关系模型必须判断能力,其模型准确,和预测的性能和行为数据库系统.关系模型已被批评为不切实际和过于简单化了,各方面的.但是,关联模型一直是大型车辆数据库研究超过十年; 这是基础,目前许多数据库; 结果,并从理论的关系数据库中找到自己的方式成为目前许多计算机系统设计方法.虽然关联模型,有许多已知的缺陷,这是大多数国家采取的数据库研究者,在70年代和80年代作为最好的数据库模型.寻找一些被广泛接受为较佳工作仍在进行中.关联模型是一种特定类型的理论模型:这是一个数据模型.数据模型提供了一种手段,即数据和关系数据的项目.该法还规定,在办法中的数据可以使用.数据模型,将包括三部分