英语翻译To implement the relational model for the same partial LIMS schema presented in Fig.1 for the hierarchical model,tables would need to be created for each entity relationship in the schema.Fig.3 shows the mapping required in the relational

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英语翻译To implement the relational model for the same partial LIMS schema presented in Fig.1 for the hierarchical model,tables would need to be created for each entity relationship in the schema.Fig.3 shows the mapping required in the relational
英语翻译
To implement the relational model for the same partial LIMS schema presented in Fig.1 for the hierarchical model,tables would need to be created for each entity relationship in the schema.Fig.3 shows the mapping required in the relational model for the Customer-Plant and Plant-Grade relationships of the LIMS schema,where each customer (company) has one or more plant sites and each plant purchases one or more grades of products.A table is created for the Customer,which includes fields for Customer ID and Customer Name.A table is also created for the Plant,which contains the Customer ID,Plant ID,Plant Name,and Plant Address.In this situation,the Customer ID would be the primary key in the customer table,but the secondary key in the plant table.It links the information contained within the two tables and implicitly forms a relationship between the two entities.To describe the Plant-Grade relationship,Grade and Plant-Grade tables are added.
Instead of direct navigation as described in the hierarchical and network models,the relational model requires joins for the Customer,Plant,and Grade tables to find out which Customer purchases a particular Product-Grade.Fig.3 shows that in order to navigate to a related record,the secondary key is used to find the primary key in an index file,which contains a sorted list of keys and physical addresses for each table record.Multiple database accesses are usually required to locate one record in an index,and as the table grows larger,the more database accesses are required.This is why relational databases slow down as they get larger.
Unlike the hierarchical and network databases,which depend on the physical structure of data,a relational database provides data independence,which means that the physical and logical structures are separated so that the user applications do not have to worry about the actual physical address of data.Other features of relational databases include concurrency,recovery,transaction,and an ad hoc query facility.
2.3.1.Client-server relational model
Originally all database files were stored on mainframes or minicomputers.Since dumb terminals were used to access the host computer,all processing occurred on the host.Relational databases were developed in this environment,in which the database server resided on the host and the application programs were processes on the host.When a large number of users needed access to the database information simultaneously,a bottleneck occurred on the host CPU.Dumb terminals were eventually replaced with powerful microcomputer workstations and the Client server architecture was developed to take advantage of the power of the workstation.The application processes were now run on the clients,while the database server remained on the host.

英语翻译To implement the relational model for the same partial LIMS schema presented in Fig.1 for the hierarchical model,tables would need to be created for each entity relationship in the schema.Fig.3 shows the mapping required in the relational
实施关联模型相同的部分实验室颁发的模式图. 1分层模型,图表将要创造每个实体的关系模式. 无花果. 3显示映射所需的关联模型,为客户提供厂房和厂级关系的LIMS的模式, 如果每个客户(公司)都有一个或多个厂址和各厂采购的一个或多个档次的产品. 一张桌子,是创造客户,其中包括领域,为客户ID和客户姓名. 一张桌子,也创造了植物,其中包含客户的身份证,身份证植物,植物名称,工厂地址. 在这种情况下,客户的身分将是主要的关键在客户表但关键中的表厂. 它把载有信息的两张桌子和默示形式关系的两个实体. 描述厂级关系,等级和厂级表. 不是直接通航所描述的层次和网络模型, 关联模型需要加入的客户,工厂, 分级表,以找出哪些客户购买某一特定产品档次. 无花果. 3表明,以切换到了相关的记录, 中学主要是用来寻找的首要关键,在一个索引文件, 其中包含一个排序名单钥匙和物理地址,每个表记录. 多重数据库的通道,通常需要寻找一个记录的一个指标,如表较大增长, 更多的数据库访问要求. 这就是为什么关系数据库慢,因为他们得到较大. 不像分层和网络数据库,而这取决于数据的物理结构数据, 关系型数据库提供了数据的独立性, 这意味着物理和逻辑结构分离,使用户应用不必担心对实际的物理地址的数据. 其他特点关系数据库包括并发,恢复交易,专案查询设施. 2.3.1 . 客户机-服务器关联模型原先所有数据库文件存放于主机或微型计算. 自从哑终端被用于接电脑主机,所有加工发生在东道主. 关系数据库开发者在这个环境中, 其中数据库服务器居住在主机与应用程序的过程中的主人. 当大量的用户需要获取数据库中的信息,同时,瓶颈发生于主机CPU . 哑终端被取代,最终以强大的微机工作站和客户服务器结构,开发利用权力的工作站. 该应用程序正运行于客户,而数据库服务器停留于东道主.

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