Speci cationformalismsinwhichcausalityandindependenceofactionscanbeexplicitlyexpressedarebene cialfromadesignpointofview.Theexplicitpresence(orabsence)ofacausaldependencybetweenactionscanbeusede ectivelyduringthedesign.Weconsideraspeci cationformal-isminwhichcausalrelationsbetweenactionsplayacentralroleandprovideasemanticsintermsof(anextensionof)labelledplace/transitionnets.Thebehaviourofnetsisde nedbylabelledpartiallyorderedsets.