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XPath Basics

TIBCO ActiveMatrix BusinessWorks uses XPath (XML Path Language) to specify and process elements of data schema. These data schema are either process variables or input schema for an activity. You can also use XPath to perform basic manipulation and comparison of strings, numbers, and booleans. To use XPath in TIBCO ActiveMatrix BusinessWorks, you need only be familiar with the basic XPath concepts, but you may wish to learn more about XPath when building complex expressions. For a complete description of XPath, refer to the XPath specification (which can be obtained from www.w3.org).

Addressing Schema Elements

All process data and activity input are represented as an XML schema. Regardless of where the data comes from or its format, TIBCO ActiveMatrix BusinessWorks represents the data as a schema tree. The data can be simple (strings, numbers, booleans, and so on), or it can be a complex element. Complex elements are structures that contain other schema elements, either simple elements or other complex elements. Both simple and complex elements can also repeat. That is, they can be lists that store more than one element of the given type.

XPath is used to specify which schema element you would like to refer to. For example, the following schema may be available for an activity’s input:

The process data area of the example input tab illustrates the output schema of the activities in the process. There are three output schema, each a root node in the process data area: GetCustomerInformation, GetOrderInformation, and GetOrderId. Each of these schema has its own associated structure, for example, GetCustomerInformation has a set of simple values and GetOrderInformation has simple data and other complex data.

To reference a particular data item in any of these schema, you start with the root node and then use slashes (/) to indicate a path to the desired data element. For example, if you wish to specify the Street attribute in the ShipName complex element that is in the GetOrderInformation node, you would use the following syntax:

 

$GetOrderInformation/ShipName/Street

The path starts with a dollar sign to indicate it begins with a root node, then continues with node names using slashes, like a file or directory structure, until the desired location is named.

Evaluation Context

XPath also has a method for referencing relative paths from a particular node. If you have an evaluation context, or a particular starting node in a schema tree, you can specify the relative path to other elements in the tree.

For example, if your evaluation context is $GetOrderInformation/ShipName, then you can reference the sub-items of ShipName without specifying the entire path. If you wish to reference $GetOrderInformation/RequiredDate, the relative path would be ../RequiredDate. The path is relative to the evaluation context — RequiredDate is one level higher in the schema tree than the elements of ShipName.

Namespaces

Some schema elements must be prefixed with their namespace. The namespace is automatically added to elements that require this when creating mappings on the Input tab of an activity or when dragging and dropping data in the XPath formula builder.

Search Predicates

An XPath expression can have a search predicate. The search predicate is used to locate a specific element of a repeating schema item. For example, the $GetOrderInformation/OrderDetails/OrderItem item is a repeating element. If you wish to select only the first item in the repeating element, you would specify the following:

 

$GetOrderInformation/OrderDetails/OrderItem[1]

The [1] specifies the first element of a repeating item.

Sub-items can also be examined and used in a search predicate. For example, to select the element whose ProductId is equal to "3A54", you would specify the following:

 

$GetOrderInformation/OrderDetails/OrderItem[ProductId="3A54"]

You can also use functions and expressions in the search predicate. For example, if you wish to find all elements after the first, you would specify the following:

 

$GetOrderInformation/OrderDetails/OrderItem[position()>1]

See the online documentation available in the XPath formula builder for a list of the available operators and functions in XPath.

You can also build custom Java functions and make them available in XPath by using the Java Custom Function shared resource. See the description of the Java Custom Function shared configuration resource in TIBCO ActiveMatrix BusinessWorks Palette Reference for more information about creating custom functions and making them available in XPath.

Testing For Nil

Some elements can be explicitly set to nil. You can test an element to determine if it is set to nil or not. For example, the following XPath expression returns true if the $Order/Item/OnSale element is set to nil:

 

$Order/Item/OnSale/@xsi:nil="true"

Comments

You can add comments to XPath expressions using the XPath 2.0 syntax for comments. The syntax is:

 

{-- <comment here> --}

For example, the following XPath expression contains a comment:

 

$GetOrderInformation/ShipName/Street {-- returns the street --}

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