by pat helland
microsoft corporation

summary: pat helland explores service oriented architecture, and the differences between data inside and data outside the service boundary. additionally, he examines the strengths and weaknesses of objects, sql, and xml as different representations of data, and compares and contrasts these models. (26 printed pages)

总述：pat helland探询soa以及服务的内外数据。他还调查了作为数据表现的不同形式的对象，sql，xml的有缺点，比较这些模型。

contents

introduction
the shift towards services
assumptions about service oriented architecture
outside data: sending messages
outside data: reference data
data on the inside
data: then and now
representations of data: inside and outside
conclusion

introduction

up until now, most of the discussions on service oriented architecture (soa) revolved around topics about integration of disparate systems, leveraging companies existing assets, or creating a robust architecture. all of these issues are relevant to soa. yet, there are other significant and engaging issues involving soa that are worth close attention. in its goal to connect heterogeneous and autonomous systems, soa adheres to several core design principles. one of the principles maintains that independent services involve pieces of code and data interconnected through messaging.

到现在为止，大部分关于soa讨论的topic都是关于异构系统的集成，有效利用公司先存资产【译者:遗留系统的利用】以及创建robust的架构。所有这些都是和soa相关的。然而，还有其他关于soa非常有意义的，很吸引人的方面值得关注的.在soa连接异构自治系统的目标中，soa坚持几个核心设计原则。其中原则之一就是通过消息传送来维护独立的服务，包括代码和交互的数据。

indeed, services are inextricably tied to messaging in that the only way into and out of a service are through messages. however, services still operate independently of each other. because of the unique relationship between services and messages, architects, developers, and programmers alike began asking critical questions. some of the questions deliberated on were how does data flow between services, how are messages defined, what data is shared, how is data inside of a service different from data outside a service, and how is data represented inside and outside services.

实际上，服务是不可避免的和消息传送绑定在一起的，因为传入传出服务的唯一方法就是通过消息。然而，服务仍然独立于彼此运行。因为服务和消息之间的唯一的联系方式，架构师，开发者，程序员都类似的开始问关键的问题。一些疑问是关于服务间数据如何流动，消息如何定义，那些数据是共享的，服务内部的数据和服务外部的数据区别，服务内外部的数据如何表示。

findings to these questions exposed seminal differences between data on the inside of a service and data that existed outside of the service boundary. data outside a service is sent between services as messages and must be defined in a way understandable to both the sending service and the receiving service. data inside a service is deeply rooted in its environment. unlike data outside services, data on the inside is private to the service. in fact, it is only loosely correlated to the data on the outside.

通过这些问题，可以发现服务内部的数据和存在于服务外部边界外部的数据之间的本质却别。服务外部的数据作为消息在服务间传送，必须以一种发送方服务和接受方服务都可以理解的方式定义。服务内部的数据是和他的环境紧密相关的。不象服务外部的数据，服务内部数据是服务的私有数据。实际上 ，它只是和服务外部数据松散联系。