Although XPRESS can be used with a standalone interpreter, it is typically embedded within an application that wants to use XPRESS statements to control or customize their behavior. This application is called the host application. Two of the more important host applications within the Identity Manager system are workflow and forms.
The host application makes calls to the XPRESS interpreter and supplies services to the interpreter. One of the more important services that the host application provides is the resolution of external variable references. Expressions often reference variables that are not defined within the expression, and the host application must then provide the values of these variables. In the case of the workflow host application, an expression can reference any variable defined within the workflow process. In the forms host application, an expression can reference the value of any form field or defvar whose value is set before the expression is evaluated.