Section 5.5. BPEL and Patterns

5.5. BPEL and Patterns

BPEL fares exceptionally well in its support for support for P4 patterns. As rated by P4 members in its paper,^[5] BPEL directly supports 13 of the 20 patterns, and it indirectly supports another one. The results of the paper are captured in Table 5-5.

^[5] P. Wohed, W. van der Aalst, M. Dumas, A. H. M. ter Hofstede, "Pattern Based Analysis of BPEL4WS," FIT Technical Report, FIT-TR-2002-04.

Table 5-5. BPEL support for the P4 patterns

Pattern	Compliance (+, +-, -)	Approach	Notes
Sequence	+	sequence activity
Parallel Split	+	flow activity
Synchronization	+	flow activity followed by another activity, which will not execute until all parallel paths in the flow have completed.
Exclusive Choice	+	switch activity.
Simple Merge	+	switch activity followed by another activity, which will not execute until the one activity selected in the switch has completed.
Multi-Choice	+	flow with conditional links to the activities to be chosen.	See P4 paper, p.8f.
Sync Merge	+	Use dead path elimination to join the results of the multiple choice.
Multi Merge	-	No.
Discriminator	-	No.	See P4 paper, p.9.
Arbitrary cycles	-	Only structured loops are allowed. No goto-like constructs.
Implicit Termination	+	rlow with a link out.
Multiple Instances (MI) Without Synchronization	+	invoke in a while loop.
MI With Design Time Knowledge	+	Run each instance as a separate activity in a flow activity.
MI With Runtime Knowledge	-	Onerous.	See P4 paper, p. 11.
MI Without Runtime Knowledge	-
Deferred Choice	+	pick activity
Interleaved Parallel Routing	+-	Multiple scopes within a flow that compete for a single shared variable whose access is serialized (variableAccessSerializable is set to yes). The order of the scopes is arbitrary but serial.	See P4 paper, p. 12f.
Milestone	-	Poll for milestone in a while loop.	See P4 paper, p.14.
Cancel Activity	+	Fault out of the activity to be cancelled.
Cancel Case	+	terminate activity