Forms the base of all activities. Simply makes sure that each activity has a name. The basic activity which, through a substitution group allows requests to include activities that are not defined in this schema. Activity input forms the base of a named element that provides an untyped input stream into the activity. Activity output forms the base of a named element that provides an untyped output stream from the activity. This base element defines a sequent of "any" elements so that default output data can be defined, e.g. in the "value" output of the parameter activity. The document that is passed into the Perform operation. A sequence element describes a number of entities that should be processed by the engine in sequential order. A sequence element can contain a sequence of sub-elements where each is either an activity, another sequence or a flow. A flow element describes a number of entities that should be processed by the engine in parallel. A flow element can contain number of elements where each is either an activity, a flow or a sequence. The mode attribute value can be used to instruct a session to terminate.