A traditional requirement of Process modeling is to be able to model the items (physical or information items) that are created, manipulated, and used during the execution of a Process. An important aspect of this is the ability to capture the structure of that data and to query or manipulate that structure.

BPMN does not itself provide a built-in model for describing structure of data or an Expression language for querying that data. Instead it formalizes hooks that allow for externally defined data structures and Expression languages. In addition, BPMN allows for the co-existence of multiple data structure and Expression languages within the same model. The compatibility and verification of these languages is outside the scope of this International Standard and becomes the responsibility of the tool vendor.

BPMN designates XML Schema and XPath as its default data structure and Expression languages respectively, but vendors are free to substitute their own languages.