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1、1外文文献翻译信息管理系统开发中的数据开发随着可视化编程工具的渐渐流行(例如Visual Basic、Java、Visual C+和第四代语言)可以容易的修改用户和系统之间的接口，原型制作正成为可选择的系统开发方法论。使用原型制作可以相对地容易的改变用户报告和显示的内容和布局。在这个处理过程中，新的数据库需求可以被识别出来，因此现有的用于展开的应用程序的数据库将需要改变。甚至为要求一个新的数据库的系统而使用原型制作。在这种情况下，系统需求通过重复的开发过程中发展，获得采样数据来建造和重建数据库原型。数据库开发的三个模式结构 概念模式是对独立于任何数据库管理技术的组织数据的整体结构的细节描述。概
2、念模式定义整个数据库而无需参照数据如何被存储在计算机的辅存中。通常概念模式被描述成使用实体关系图(E-R)或对象建模符号; 我们称这种概念模式为数据模型。另外，概念模式的细节描述被存放在储存库或数据字典中作为元数据。用户观点(或外模式)也是独立于数据库技术的，但却具有代表性的地包含关联的概念模式的一个子集，与一个特殊用户或用户群有关(例如，存货管理员或应收帐款部门)。用户观点也是用于特殊程序的模式的版本（例如，一个指令输入程序)，因为一个程序是用于一个特殊用户或是用户群。因此，用户观点除了编程语言项（也就是说，和编程语言的句法相一致），也同时被定义在逻辑项（独立的技术）。通常用户观点的原始描述
3、是计算机屏幕显示、商业事务(例如一个订阅更新形式)，或者报告，因为这些显示、事务或者报告经常描述程序需要的全部数据。用户观点的一个逻辑版本可以用一个E-R图或对象图或作为联系表现出来。一个物理模式包括从概念模式而来的数据如何存储在计算机辅助存储器中的规格。对数据库分析员和设计师来说物理数据库(物理模式)的定义是重要的，它提供了分配和管理数据存储和访问的物理辅助存储空间的数据库技术的所有规格。数据库发展和数据库技术是建立在鼓励这三种数据库观点的差别的基础上的。数据库发展项目的一个角色可以这三种观点中的一个关联的任务。例如，在早期的事业中，设计外模式可能用于一个或多个程序。之后，随着经验的发展，设
4、计物理模式或概念模式。数据库设计问题在各层间变化。总的来说，概念模式，外模式和物理模式形成了数据库三个模式的系统结构。在概念模式的第一个相交处是基于根据组织的企业数据模型和对项目数据库要求的一般理解而发展起来的。然后对于每个传输、报告、屏幕显示和其他系统使用的外模式（用户观点）被开发出来。在大多情况下，一种对外模式的分析将产生在概念模式中没显示的新的属性和可能的实体和关系。因此，概念模式随着概念性和外模式的调和而增加。当新的用户观点被识别时，概念模式和外模式的演变过程将重复。为了开始开发数据库和它关联的应用程序，要为关联的物理模式的编写规范。除了概念模式和外模式外，当用与它相关联的物理模式设计
5、物理数据库时，也要考虑硬件和软件特征和用户对数据库性能的期望。在物理数据库的设计中可能会遇到概念模式或用户观点的矛盾或是其他问题，因此循环回到这些设计步骤是可能的。当另外的用户要求以后被识别时，这个过程再次开始。通常新的要求经常批量出现，在外模式和概念模式设计中的新的循环将被共同考虑，因此数据库不能经常的改变。数据库的周期性修改发生在系统开发维护阶段。 2外文文献原文Data Development within Information Management Systems DevelopmentWith the increasing popularity of visual programm
6、ing tools (such as Visual Basic, Java, Visual C+, and fourth-generation languages) in which it is easy to modify the interface between user and system, prototyping is becoming the systems development methodology of choice. With prototyping it is relatively easy to change the contents and layout of u
7、ser reports and displays. During this process, new database requirements may be identified, and hence existing databases used by the evolving application will need to change. It is even possible to use prototyping for a system that requires a new database. In this case, sample data are acquired to b
8、uild and rebuild the database prototype as the system requirements evolve through the iterative development process.Three-Schema Architecture for Database Development A conceptual schema is a detailed specification of the overall structure of organizational data that is independent of any database m
9、anagement technology. A conceptual schema defines the whole database without reference to how data are stored in a computers secondary memory. Usually a conceptual schema is depicted in graphical format using entity-relationship (E-R) or object modeling notations; we have called this type of concept
10、ual schema a data model. In addition, specifications for the conceptual schema are stored as metadata in a repository or data dictionary.A user view (or external schema) is independent of database technology but typically contains a subset of the associated conceptual schema, relevant to a particula
11、r user or group of users (for example, an inventory manager or accounts receivable department). A user view is also the version of the schema used in a particular program (for example, an order entry program), because a program is used by a particular user or group of users. Thus, a user view is def
12、ined in both logical (technology-independent) terms as well as programming language terms (that is, consistent with the syntax of the programs language). Often the original depiction of a user view is a computer screen display, business transaction (such as a subscription renewal form), or a report
13、since each of these often depicts all of the data needed by a program that processes that display, transaction, or report. A logical version of a user view can be represented as an E-R or object diagram or as relations. A physical schema contains the specifications for how data from a conceptual sch
14、ema are stored in a computers secondary memory. Of importance to the database analyst and designer is the definition of the physical database (the physical schema), which provides all the specifications to the database technology to allocate and manage physical secondary memory space where data are
15、to be stored and accessed.Database development and database technologies are based on encouraging the distinction among these three views of databases. A role on a database development project may deal exclusively with tasks associated with only one of these three views. For example, early in a care
16、er, one may design external schemas used in one or more programs. Later, with experience, one will design physical schemas or conceptual schemas. Database design issues vary across the levels.Together, conceptual, external, and physical schemas form the three-schema architecture for databases. A fir
17、st cut at the conceptual schema is developed based on the organizations enterprise data model and the general understanding of database requirements on a project. Then external schemas (user views) for each transaction, report, screen display, and other system use are developed. In most cases, an an
18、alysis of the external schemas will yield new attributes and possibly entities and relationships not shown in the conceptual schema. So, the conceptual schema is augmented with the conceptual and external schemas consistent. When new user views are identified, this process of evolving both the conce
19、ptual and external schemas repeats.To begin developing the database and its associated application programs, write the specifications for the associated physical schema. Besides the conceptual and external schemas, also consider hardware and software characteristics and users database performance ex
20、pectations while designing the physical database with its associated physical schema. It is other issues with the conceptual schema or user views will be encountered, so it is possible to cycle back to these design steps. When additional user requirements are identified later, the process begins again. Usually new requirements are batched and considered together in a new cycle of external and conceptual schema design, so that the database is not constantly changing. Periodic revisions of the database occur during the Maintenance phase of systems development. - 4 -