Variables are named data type instances that are accessible by all activities within a business process definition. Variables can have simple data types (string, integer, float, or boolean) or XSD complex data types.
Context Variable
You can define context variable using the variable object, message formats, message parts, and XML element types.
Designing XSD Data Types
XSD schema files contain the definition of the complex data types used within the business process. These data types are used to define context variables that are accessible by the different activities.