XML Web 服务基础(Technology Computer English)

XML Web services are the fundamental building blocks in the
move to distributed computing on the Internet. Open standards and the
focus on communication and collaboration among people and applications
have created an environment where XML Web services are
becoming the platform for application integration. Applications are
constructed using multiple XML Web services from various sources that
work together regardless of where they reside or how they were
implemented.
There are probably as many definitions of XML Web Service as
there are companies building them, but almost all definitions have these
things in common:
n XML Web Services expose useful functionality to Web users
through a standard Web protocol. In most cases, the protocol used is
SOAP.
n XML Web services provide a way to describe their interfaces
in enough detail to allow a user to build a client application to talk to
them. This description is usually provided in an XML document called
a Web Services Description Language (WSDL) document.
n XML Web services are registered so that potential users can
find them easily. This is done with Universal Discovery Description
and Integration (UDDI).
One of the primary advantages of the XML Web services
architecture is that it allows programs written in different languages
on different platforms to communicate with each other in a standards-
based way. Those of you who have been around the industry
a while are now saying, "Wait a minute! Didn't I hear those same
promises from CORBA and before that DCE? How is this any
different?" The first difference is that SOAP is significantly less
complex than earlier approaches, so the barrier to entry for a
standards-compliant SOAP implementation is significantly lower. You'll
find SOAP implementations from most of the big software companies,
as you would expect, but you will also find many implementations
that are built and maintained by a single developer. The other
significant advantage that XML Web services have over previous
efforts is that they work with standard Web protocols-XML, HTTP
and TCP/IP. A significant number of companies already have a Web
XML Web 服务是互联网分布计算的基本构件块。开放
的标准、对通信的关注、人与应用软件之间的协作创建了一
个环境，在这个环境中，XML Web 服务正成为应用软件集
成的平台。应用软件用来自于各种资源的XML Web服务构
建，这些资源协同工作，不管它们位于何处、如何实现。
XML Web 服务的定义几乎与开发它们的公司一样多，
但几乎所有的定义都有以下共同点：
n XML Web 服务通过标准Web 协议向Web 用户提供
它的有用功能。在多数情况下，使用的协议是简单对象访问
协议（SOAP）。
n XML Web服务提供了详细描述接口的方法，以便用
户开发客户端应用并与之通信。这种描述通常包含在称为
Web 服务描述语言（WSDL）文档的XML 文档中。
n 要注册XML Web 服务，使潜在用户容易地找到它
们，这用通用发现描述和集成（UDDI）完成。
XML Web 服务体系结构的一个主要优势是：它允许在
不同平台上、用不同语言编写的程序以标准方法相互通信。
你们中的业界新人可能会说：“ 等等！ 难道我没有听过
CORBA 和在此之前DCE（分布计算环境）的类似承诺，它
们有何区别？”第一个不同之处是SOAP比早期方法简单得
多，实现与标准兼容的SOAP，障碍也少得多。正如你预料
的，多数大软件公司都提供SOAP实施方案，你也会发现有
许多由单个开发人员开发和维护的实施方案。与以前其它技
术相比，XML Web 服务的另一个明显优势是它采用标准的
Web 协议即XML、HTTP 和TCP/IP。很多公司已经有Web
基础设施、知识和维护经验丰富的人力资源。因此，进入
XML Web 服务的成本明显低于以前的技术。

 infrastructure, and people with knowledge and experience in maintaining
it, so again, the cost of entry for XML Web services is
significantly less than previous technologies.
We've defined an XML Web service as a software service
exposed on the Web through SOAP, described with a WSDL file
and registered in UDDI. The next logical question is. "What can I
do with XML Web services?" The first XML Web services tended to
be information sources that you could easily incorporate into applications-
stock quotes, weather forecasts, sports scores etc. It's easy
to imagine a whole class of applications that could be built to
analyze and aggregate the information you care about and present it
to you in a variety of ways; for example, you might have a
Microsoft(r) Excel spreadsheet that summarizes your whole financial
picture-stocks, 401K, bank accounts, loans, etc. If this information
is available through XML Web services, Excel can update it
continuously. Some of this information will be free and some might
require a subscription to the service. Most of this information is
available now on the Web, but XML Web services will make
programmatic access to it easier and more reliable.
Exposing existing applications as XML Web services will allow
users to build new, more powerful applications that use XML Web
services as building blocks. For example, a user might develop a
purchasing application to automatically obtain price information from
a variety of vendors, allow the user to select a vendor, submit the
order and then track the shipment until it is received. The vendor
application, in addition to exposing its services on the Web, might
in turn use XML Web services to check the customer's credit,
charge the customer's account and set up the shipment with a
shipping company.
In the future, some of the most interesting XML Web services
will support applications that use the Web to do things that can't be
done today. For example, one of the services that the Microsoft .NET
My Services project will support is a calendar service. If your dentist
and mechanic exposed their calendars through this XML Web service,
you could schedule appointments with them on line or they could
schedule appointments for cleaning and routine maintenance directly in
your calendar if you like. With a little imagination, you can envision
hundreds of applications that can be built once you have the ability to
program the Web.
While much work has been done to make XML Web services a
reality, more is needed. Today, people are having success with XML
Web services, but there are still things that are left as an exercise for
the developers e.g. security, operational management, transactions,
reliable messaging.
我们把XML Web 服务定义为通过SOAP 在Web 提供的
软件服务，这种服务用WSDL文档描述、在UDDI中注册。那
么你自然要问“使用XML Web能做什么？”最早的XML Web
服务旨在成为信息源，你能容易地把这些信息源如股票报价、
天气预报、体育成绩等并入应用软件中。容易想象，能开发一
类应用软件去分析和集成你关注的信息，并以各种方法提供给
你。例如：你用微软的电子表格（Excel）汇总整个财务信息
如股票、401K、银行存款、货款等。若这种信息能通过XML
Web服务得到，电子表格就能不断更新。这种信息，有些是免
费的，有些需要定制。这种信息大多数在Web 上能找到，而
XML Web服务将使编程访问更容易和更可靠。
把现有的应用软件作为XML Web服务提供，将允许用
户构建新的、更强大的应用软件，这些新应用软件将把XML
Web服务用作构件块。例如，一个用户要开发一个采购应用
软件、以自动获取各个供应商的价格信息、允许用户选择供
应商、提交订单、跟踪物流运输。这种供应商应用软件，除
了在Web上提供服务外，还要用XML Web服务去检查顾客
信用、对用户帐户收费、与物流公司办理物流手续。
将来，一些最有趣的XML Web服务会支持应用软件利
用Web去做在今天无法做到的事情。例如：微软.NET的“我
的服务工程”将支持的一个服务是日程表服务。若你的牙医
和维修工通过这种XML Web服务提供他们的日程表，你便
能与他们在线约会，如你愿意，他们可直接在你的日程表上
预约清理和安排维护工作。不难想象，一旦有能力编写这种
Web，你就可以构建数百种应用软件。
虽然人们已经做了许多工作去实现XML Web服务，但
需求仍在增加。今天，人们已经在XML Web服务上取得了
成功，但有些环节仍待开发者完善，如安全、运行管理、事
务、可靠信息传递等。