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此文来自Tuscany 邮件列表<tuscany-user@ws.apache.org>，由Raymond Feng 所写。原文为英文，此处根据自己的理解翻译为中文，不正之处，请修改
1) target 属性
a)一个SCA中的service可表示一个业务功能，该功能由component提供。比如，一个书店提供卖书的服务。
b)一个SCA中的reference表示某个component所需要使用的业务功能。比如，书店需要用到购物车和目录。
1) @target

a) An SCA service represents a business function that a component provides,
for example, a book store selling books.
b) An SCA reference represents a business function that a component
consumes, for example, book store needs to use shopping cart and catalog.

The 'target' attribute of <reference> points to an SCA service that can
provide the business function required by the reference. For example, if the
BookStore component has a catalog reference as follows: reference的属性target 指向该reference所需的service。如下：
BookStore component有一个reference

<component name="BookStoreComponent">
<reference name="catalog" target="CatalogComponent/Catalog"/>
</component>

<component name="CatalogComponent">
<service name=Catalog></service>...
</component>

The @target says CatalogComponent's Catalog service is the provider for
catalog reference. If you change it to "NewCatalogComponent/Catalog", you
basically switch to a new service provider: NewCatalogComponent's Catalog
service.

target属性的意思是，CatalogComponent 的Catalog Service是catalog reference的提供者。
如果我们将CatalogComponent改名为NewCatalogComponent,那么相应的target改为：NewCatalogComponent/Catalog.

2) promote属性
在SCA中，可以采用<implementation.composite>来在一个composite中使用另一个compoiste。比如，Catalog service本身可以以composite的形式部署，
在Catalog composite中，可以用2) @promote

In SCA, a pre-assembled composite can be reused as a building block for
compositions. It's achieved by <implementation.composite>. For example, the
Catalog service itself can be developed as a SCA composite. Inside the
Catalog composite, there could be a few java components.

...