The documentation suggests that the Workflow component is based on Petri Net but the docs are not complete enough to determine if it supports the requirted routing constructs (AND-split, AND-join, ORsplit and OR-join) to build sequential, conditional, parallel, and iterative routings. See the "4.2 Routing constructs" chapter in The Application of Petri Nets to Workflow Management. To rephrase the question for the Workflow component specifically: how do I add conditional branching to workflows?

EDIT by @lyrixx: The new location for the PDF: http://workflowpatterns.com/documentation/documents/vanderaalst98application.pdf (thanks #20879 (comment))