Join conditions are evaluated by the target activities of links. With the drop-down Expression language menu, enter an XPath expression that defines the condition of the join. The Suppress Join Failure behavior defined by the process or a containing scope can be overridden with the radio buttons at the bottom.

The Correlation tab lists all correlations that are used by the currently selected Receive, Reply or Invoke activity. Correlations can be added to or removed from the activity through this tab.

Namespaces are URIs (Uniform Resource Identifiers) that uniquely identify a set of resources on the Internet. Because URIs can be very lengthy, shorthand aliases called prefixes are typically defined and used in XML files to make the XML more readable.

The Namespaces tab lists all of the namespace URIs and their prefixes in scope for the currently selected activity. Whenever you create a reference to an external property (an element defined in an XSD) whose namespace has not yet been assigned a prefix, the BPEL Designer will prompt you to create a prefix. This can also be done beforehand through the Namespace tab of the Properties sheet for the property by clicking the Assign Prefix button.

The Process Details tab allows you to select the default Expression and Query language. If you set Exit on Standard Fault to Yes, it will cause the process to terminate if a WS-BPEL standard fault, other than a join failure, is encountered.

The Imports Detail tab lists all of the imported service interfaces (WSDL) and XML Schemas (XSD) used by the process. Additional WSDL and XSD files can be added to the imports on this page. After a new resource has been imported, you may assign a prefix to the namespace URI from the Namespaces tab.

Partner Links help define the conversations between two services. They define the roles each partner plays in the conversation and the types of messages that can be exchanged between them.

The Details tab allows you to choose the Expression language and Query language for selecting elements of a Partner Link.

Variables are used in BPEL to store inbound and outbound messages for examination and manipulation by the business logic; they can also be used to save intermediate results and the process state. There are three kinds of variable declarations: messages types, XML Schema types and XML Schema elements.

The Details tab allows you to define the variable declared type and its structure by selecting from known types. Once a variable type has been defined, the structure of the variable is shown. Clicking on the hyperlink will open the WSDL or XML Schema editor for the selected type or element.

The Empty activity is a placeholder for any undefined Basic Activity and is intended to eventually be replaced by a real activity before the process can actually be executed. If the BPEL engine encounters an Empty activity, it is ignored.

The Details tab allows you to select one of four basic actions: Invoke, Receive, Reply and Assign. Hovering the mouse over one of the selection buttons displays a brief description of that activity.

The Invoke activity requires a Partner Link name and an Operation as defined in the WSDL for that service. You can use the Quick Pick tree control at the right to select the Partner Link and Operation. For one-way invocations of the service, specify only an Input Variable; for request-response invocations you must also specify an Output Variable.

The checkbox labeled Use WSDL Message Parts Mapping provides an alternative to using variables for the request message.

A Receive activity requires a Partner Link name and an Operation as defined in the WSDL for this service. You can use the Quick Pick tree control at the right to select the Partner Link and Operation. A previously defined variable can be used to hold the message data, or the Use WSDL Message Parts Mapping checkbox can be set to store the incoming message in an anonymous WSDL message variable.

The Create a new Process Instance checkbox, when enabled, will cause the BPEL engine to start a new process. This will start a new conversation with a client.

A Reply activity requires a Partner Link name and an Operation as defined in the WSDL for this service. You can use the Quick Pick tree control at the right to select the Partner Link and Operation. A previously defined variable can be used to provide the response message data, or the Use WSDL Message Parts Mapping checkbox can be set to use the data from the anonymous WSDL message variable.

The following figure shows the detail tab of an Assign activity which has an XPath expression as the source (From) and a process variable element as the target (To):

A requirement of the BPEL language is that all complex variables must be initialized with valid XML before they are referenced either as a target of an assignment, or in another BPEL activity. The BPEL Designer understands this and, once you have selected the target of an assignment operation, it will ask if you would like to have an XML fragment generated for the target variable:

Unless you are certain that the variable has been initialized during a previous assignment operation or other activity, you should click Yes. The figure below shows the Assign details tab after the initializer has been generated:

Assignment Operation Categories

Additional type selection or data entry widgets will appear below the From and To combo boxes, depending on the source and target item categories selected in the combo boxes. Initially these will be controls for the selection of process variables, since the default combo box selection is Variable. The possible source and target categories are described in the following table:

The Validate details tab contains a list of variables to be validated.

These activities have the same details tab, which allows you to specify an XPath expression to be evaluated for the conditional activity.

The Link detail tab allows you to specify a condition that will cause Flow synchronization to be satisfied and allow the target activity to continue. This is similar to the details tab of the other conditional activities.

The Pick details tab allows you to specify whether the event will create a new process instance.

The OnMessage activity is used in either a Pick or event handler.

The Details tab allows you to specify the Partner Link, Operation and Message Type expected by the activity, and the process variable that will contain the received message data.

The OnAlarm activity is used in either a Pick or event handler to handle timeouts while waiting for messages to arrive. This activity can be configured to wait for a certain period of time or until a specific date and time.

The Details tab allows you to specify the Partner Link, Operation and Message Type expected by the activity, and the process variable that will contain the received message data.

Repeat conditions are only allowed for an OnAlarm in an event handler. This allows the activities enclosed in the activity to be executed repeatedly. Repeat duration is the amount of time the process will wait before each repetition. The Repeat screen follows:

The details tab of the ForEach activity allows you to specify a counter variable to be used for keeping track of the loop iterations. The Parallel execution checkbox, when enabled, will execute all iterations in parallel.

The Counter Values tab is where the required starting and ending counter values are specified.

The optional Completion tab allows you to specify the early termination condition for the loop.

The details tab of the Wait activity allows you set a delay (Duration) or specify a date and time (Date) for when to continue process execution.

The details tab for the Scope activity allows you to define whether the Scope is isolated.

The Throw activity will invoke a fault handler in an enclosing Scope activity. Throw requires the name of either a standard BPEL fault, or the name of a user-defined fault message. A variable is used to hold the value of the fault data.

The CompensateScope activity will invoke a compensation handler in the Scope or the Invoke activity given by the name of the Target Activity.

The Validate activity is used to validate the values of variables against their XML Schema and WSDL data definitions. This includes the variable’s data type as well as structure. If validation fails, the BPEL standard fault invalidVariables is thrown.

The If activity allows conditional execution of one or more sequences of activities. It consists of a sequence of one or more conditional branches defined by If and optional ElseIf elements. The elements are evaluated in left-to-right order (or top-to-bottom if you have selected horizontal layout). An optional Else branch will be executed if none of the other conditions are true.

An If activity must define a condition (expressed as an XPath) and an activity which is executed if the condition evaluates true. To insert additional ElseIf and Else elements, right-click the If figure and select the desired element from the context menu. The figure above shows a complete If activity with optional ElseIf and Else elements.

The While activity repeatedly executes the contained activity as long as a condition evaluates true at the beginning of each iteration. A While activity must define a condition and must contain an activity.

ForEach is a looping activity that executes the activities contained in its Scope a specified number of times. A counter variable, defined in the ForEach property detail tab, is used to keep track of the iterations. The ForEach properties must be configured with starting and ending value expressions for this counter variable. The counter is initially set to the starting value and activities in the Scope are executed until the counter exceeds the ending value.

This activity can also be configured to execute all iterations in parallel, meaning the enclosed Scope activity behaves as if multiple Scopes are enclosed in a Flow activity.

An optional early termination value can be defined, which will cause the loop to complete before the counter has reached its ending value. The ForEach will complete when the counter is equal to this early termination value for the sequential execution case. For the parallel execution case, the early termination value is the number of completed iterations. For example, the ForEach completes when at least some number of some action have finished.

The RepeatUntil activity repeatedly executes the contained activity as long as a condition evaluates true at the end of each iteration. A condition must be defined for a RepeatUntil, and it must contain an activity.

If it were necessary to perform an assignment and then invoke another web service, the Assign and Invoke could be contained within a Sequence. The Sequence would then become the target of the If:

A Scope provides a context for its enclosed activity. This context includes variables, partner links, message exchanges, correlation sets, event handlers, fault handlers, a compensation handler and a termination handler. These Scope contexts can be nested hierarchically where the root context is provided by the process itself.

In this example, the Billing department can begin preparation of a customer invoice, but it needs to know if sufficient stock is on hand to fulfill the order and if an outside vendor needs to provide the additional quantities ordered. The following condition would enable the Link so that execution can continue for the price calculation and customer invoicing:

This process is only partially complete though as it does not consider the number of outside vendors, or if the total quantity being ordered can ever be filled.

The Exit activity causes the process to immediately terminate.

The Throw activity propagates a specified fault to its ancestor Scope, or the process itself.

A Rethrow activity can only be used inside a fault handler. It is used to propagate the fault that was caught by the handler, using the original fault data.

The Compensate activity is used to invoke a compensation handler. This activity can only be used within a fault handler, compensation handler or termination handler.

The CompensateScope activity is used to invoke a compensation handler in the enclosing Scope. This activity can only be used within a fault handler, compensation handler or termination handler.

Fault and event handlers can be defined for the process by right-clicking the Start activity and selecting the desired handler from the context menu.