Petri Net Markup Language
The Petri Net Markup Language (PNML) is a proposal of an XML-based interchange format for Petri nets. PNML is a concept for defining the overall structure of a Petri net file. There are many different types of Petri nets. Thus, there is a generic concept for adjusting net type specific features via a specific Petri Net Type Definition (PNTD).
For implementing a specific PNTD PNML is enlarged by type specific labels at certain net objects. A label assigns further meaning (besides the Petri net semantics) to a net or its objects. Typically, a label represents a name of a node, the initial marking of a place, the guard of a transition, or the inscription of an arc. The legal labels and the legal combination of labels are defined within a PNTD.
http://www.informatik.hu-berlin.de/top/pnml/