软件设计师专业英语(1)

Computer English

Networks can be interconnected by different devices. In the physical layer, networks can be connected by repeaters or hubs, which just move the bits from one network to an identical network. One layer up we find bridges and switches, which operate at data link layer. They can accept frames examine the MAC address, and forward the frames to a different network while doing minor protocol translation in the process. In the network layer, we have routers that can connect two networks. If two networks have dissimilar network layer, the router may be able to translate between the packet formats. In the transport layer we find transport gateway, which can interface between two transport connections. Finally in the application layer, application gateways translate message syntax. As an example, gateways between Internet e-mail and X.400 e-mail must parse the e-mail message and change various header fields.

网络可以用不同的设备互连。在物理层，用中继器或集线器互连，这些设备只是在相同的网络之间传送比特串。在上面的数据链路层，可以使用网桥或交换机，这些设备接收数据帧，检查MAC地址，并可以实现少量的协议转换，把数据帧转发到不同的网络中。在网络层，我们使用路由器连接两个网络的网络层不同，路由器能够对分组格式进行转换。在传输层，我们使用传输网关，它可以在两个传输连接之间建立接口。最后，在应用层，应用网关实现消息语法之间的翻译。例如，在Internet 邮件和平X.400 邮件之间的网关可以对邮件报文进行语法分析，对报文的各个报头字段做出改变。

The purpose of the requirements definition phase is to produce a clear, complete, consistent, and testable specification of the technical requirements for the software product.

During the requirements definition phase, the requirements definition team uses an iterative process to expand a broad statement of the system requirements into a complete and detailed specification of each function that the software must perform and each criterion that it must meet. The starting point is usually a set of high – level requirements from the customer that describe the project or problem.

In either case, the requirements definition team formulates on overall concept for the system and then defines rules showing how the system will be operated, publishes the system and operations concept document, and conducts a system concept review (SCR ).

Following the SCR, the team derives outlined requirements for the system from the high level requirements and the system and operations concept. Using structured or object – oriented analysis, the team specifies the software functions and algorithms needed to satisfy each detailed requirement.

需求定义阶段的作用就是为软件产品产生一个清晰的、完整的、一致的、可测试的技术需求规格说明。

在需求定义阶段，需求定义团队通过迭代过程把有关系统需求的宽泛的陈述扩展成系统必须实现的各个功能的、完整而详细的规格说明，以及系统应该满足的各种准则。这个过程的起点通常是由用户提供的描述项目或问题的一组高级需求。

在任何情况下，需求定义团队应该阐明与系统有关的整体概念，并且设定一种能够显示系统如何动作的情景，发布有关系统和运行的概念文档，并进行系统概念的评审（SCR）。

在SCR 之后，团队应该根据高级需求和系统运行概念导出详细的系统需求。通过结构分的或面向对象的分析技术，团队可以规范系统功能，说明满足每一细节需求的算法。

Requirement ：需求定义 concept document：概念文档  review：评审          specification ：说明、描述