Services as a Paradigm of Computation - Formal Methods and Hybrid Real-Time Systems - page 531

Fig. 3. inner ( A )

communication with other services. Technically, the inner subnet inner ( N )can
be conceived as a representation of workflows. A workflow net N additionally
requires special properties of initial and final markings.

4.3 Composition of Open Workflow Nets

As outlined in the introduction, composition of services is a major concern of
SOC. Consequently, composition of service models should be as general and as
simple as possible.
We can always assume that two oWFNs M and N don't share inner elements,
but only interface places. Then the composition M

N of two oWFNs M and N
is just the (sorted) union of their elements. Figure 4 shows an example. Appendix
A2 provides formal details.

⊕

coin coin

“tea!”

“coffee!” “coffee!”

beverage beverage

oWFN B oWFN A ⊕ B

Fig. 4. Composition of services