Messaging in the process specification language

data types receive messages in a similar way to functions, but the reactions are based on the type of thing operated on, as shown in Expression 12. The SHAPEPART activity has subactivities for receiving pieces of metal and plastic, and for sending drill and mill messages, or mold and trim messages, in response. Then the last two statements of Expression 12 require receiving a shape part message to be followed immediately by sending a drilling and milling message, or molding and trimming messages, depending on whether the part is metal or plastic. (activity shapePart) (forall (?x ?occDrillAndMill) (implies (and (metal ?x) (occurrence_of ?occDrillAndMill drillAndMill)) (subactivity send-message(?x ?occDrillAndMill) shapePart))) (forall (?x ?occMoldAndTrim) (implies (and (plastic ?x) (occurrence_of ?occMoldAndTrim moldAndTrim)) (subactivity send-message(?x ?occMoldAndTrim) shapePart))) (forall (?x ?ra ?sSend) (implies (and (metal ?x) (= ?ra receive-message(?x ?sSend))) (subactivity ?ra shapePart))) (forall (?x ?ra ?sSend) (implies (and (plastic ?x) (= ?ra receive-message(?x ?sSend))) (subactivity ?ra shapePart))) (forall (?occShapePart ?sReceive ?x ?sSend) (implies (and (occurrence_of ?occShapePart shapePart) (subactivity-occurrence-of ?sReceive ?occShapePart receive-message(?x ?sSend)) (metal ?x)) (exists (?occDrillAndMill ?sSendDrillAndMill) (and (occurrence_of ?occDrillAndMill drillAndMill) (subactivity-occurrence-of ?sSendDrillAndMill ?occShapePart send-message(?x ?occDrillAndMill)) (next_subocc ?sReceive ?sSendDrillAndMill)))))