BPEL4WS1.1学习笔记[3]

Basic Activities

Standard Elements：<source><target>

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<invoke>

An asynchronous invocation requires only the input variable of the operation because it does not expect a response as part of the operation.

A synchronous invocation requires both an input variable and an output variable这些属性只在executable processes中有用。WSDL fault 由QName标识，target Namespace of the corresponding portType and the fault name.

一个acitivity可与另一个activity（作为其compensation）关联

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<receive>

business process通过<receive>&<reply>向其partner提供服务。<receive>指定了the partner link it expects to receive from,and the portType & operation that it expects the partner to invoke定义一个variable用来接收message data.

The only way to instantiate a business process is to annotate a <receive>activity with the createInstance attribute set to "yes".

Anonoted<receive> acitivities must be initial activities.

<receive>is a blocking activity

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<reply>

send a response to a request previously accepted through a <receive> activity.Such response仅对同步交互有意义。

An asynchronous response is sent by invoking the corresponding one-way operation on the partner link，可定义一个variable包含message data to be sent in reply.

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<throw>

业务流程显式地发出内部故障信号时，使用<throw>。每个故障需要有一个全局唯一的QName。<throw>活动为故障提供QName，可提供一个variable of data，提供故障的其他信息。Fault Handler可使用such data分析处理fault。

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<wait>

允许business process specifies a delay for a certain period of time or until a certain deadline is reached.

<wait (for = "duration-expr"|until = "deadline-expr") ></wait>

典型的应用是invoke an operation at a certain time(一般是个常数，或依赖流程状态的表达式)

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<empty>

When a fault needs to be caught and suppressed.

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Structured Activities

规定了一组活动发生的顺序。

1. 活动间的一般顺序<sequence><while><switch>
2. 活动间的并发和同步<flow>
3. 基于外部时间的不确定的选择<pick>

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<sequence>

一个sequence包含一个或多个按顺序执行的活动，in the order in which they are listed within the <sequence> element.The sequence activity completes when the final activity in the sequence has completed.

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<switch>

由有序的一个或多个条件分支组成<case>可能有<otherwise>分支。选择条件为true的第一个分支并执行其活动。如果都不符合，选<otherwise>。如<otherwise>未显式制定，an otherwise branch with an <empty>活动将被执行

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<while>

支持repeated performance of a special iterative activity. Until the given Boolean thile condition no longer hold true.

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<pick>

等待一组事件中的一个发生，然后执行与发生的事件相关的活动。事件的发生往往是互斥的。如果不止一个事件发生，选最先发生的那个。

<pick>是一组形为event/activity的分支，当pick接收到一个event后，便不再接收其他events。

可能的事件：

1. 消息的到达——调用进站的单向操作或request/response操作。
2. alarm based on a timer

case：接收到一个消息而创建流程实例，pick本身的createInstance的值是yes（缺省为no），pick中的event必须为进站消息。

每个<pick>必须包含至少一个onMessage Event.

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<flow>

提供并发（concurrency）和同步（synchronization）

如果一个活动的使能条件为false，该活动被跳过。从而终止。

<link>用来表达synchronization dependencies.

<source><target><transitionCondition>source 和 target中都要指定linkName.

links可以跨越结构化活动的边界。

link不能跨越活动<while>,serializable scope,event handler,compensation handler的边界

A->B link是A的outgoing link（出站）

B->A link是A的incoming link（进站）

Y->X X has a synchronization dependency on Y.

每个座位link target的活动都有一个implicit or explicit joinCondition属性与之关联。

要求至少一个incoming link的status为positive.

joinCondition is a Boolean experession

该表达式由Boolean operators & thebpws:getLinkStatus函数来构造。

1. A的outgoing link的status positive or negative确定某个link的状态，需要求出transition Condition
2. A->B B is ready to start; B 的所有incoming links 的status被确定。
3. 如果1.2条件都true，求B的join condition的值；如果join Condition值为false，bpws:joinFailure抛出，否则activity B is started.

如果一个有多个outgoing links 的活动完成，enable多个target activities such an antivity is often called a "fork activity".

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