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Expression Data Form Drives Expressions on the Status Page

A page may contain a reference to an Expression Data Form, which is a type of ViewDataForm. An Expression Data Form is never actually displayed in the UI. Instead it acts behind the scenes to gather important information about the displayed record and make it available to the page. This allows the page author to write regular expressions to dynamically alter what is displayed on the page.

Within the PageDefinitionSpec XML element is an attribute named ExpressionDataFormID. The ExpressionDataFormID attribute specifies a View Data Form instance to use as a source for expressions within a page. The expression model similar to the one found in Microsoft Reporting Services or in various dialects of Visual Basic.

Looking at the metadata for the completed food bank inventory business process status page below, we can see it leverages an Expression Data Form named "Inventory Process Business Process Status View Form." 

Figure: The status pages utilizes and expression view data form

We can click on the link for the Expression Data Form (Inventory Process Business Process Status View Form) to view its metadata.

Figure: Expression Data Form metadata page displays the form fields retrieved

Three fields are provided by the data form: Name, BusinessProcessCatalogID, and ParameterSetID. The Nameform field represents the value of the USR_INVENTORYPROCESS.Name column which is the name of the parameter set used by this business process instance. The Nameform field is used to dynamically display the caption for page. The BusinessProcessCatalogIDform field represents the ID attribute value from the BusinessProcessSpec used to create the food bank inventory business process. The ParameterSetIDform field represents the primary key value of the parameter set used to by this business process instance. The ParameterSetIDform field value is used within an expression to provide the context for the Create job scheduleaction within the Tasksaction group on the left hand side of the page.

Figure: Expression data dorm fields drive expressions on the status page