Requirements as Goals and Commitments Too - Intentional Perspectives on Information Systems Engineering - page 142

Fig. 3 Three possible enactments of the protocol of Table 1
manipulated. Traditional approaches force a tradeoff: checking compliance is sim-
ple with rigid automaton-based representations and difficult with flexible reasoning.
Protocols specified using commitments find the golden mean, promoting flexibility
by constraining interactions at the business level, yet providing a rigorous notion of
compliance.
2.4 Architecture, Interoperability, and Middleware
In the discussion above, we used examples where the commitments are defined over
specific agents (for example, Alice and EBook). General protocols can be defined
by stating the commitments among roles instead of agents. For example, we can
replace Alice with Customer and EBook with Vendor and use the commitments
of the previous sections to specify a general protocol for commercial transactions.
These generic protocols can then be used in a specific context by binding a specific
agent to each role of the protocol.
Protocols are architectural specifications: they specify the interconnections
between agents (via roles). Commitment protocols abstract away from consider-
ations of control and data flow, instead focusing on the contractual relationships
among agents. This affords agents flexibility in protocol enactment. However, flex-
ibility poses challenges for interoperability: if an agent may send any message at
any time, how do we ensure that they will come to the same conclusion about their
commitments towards each other? Example 6 illustrates a case of misalignment .
Example 6. Assume both Alice and EBook infer c B . Subsequently, Alice's payment
for the topic and EBook's cancellation of the offer c B cross in transit (we are dealing
with distributed systems). When Alice receives EBook's cancellation, she considers
it as having arrived too late; EBook considers Alice's payment late. Thus, Alice
concludes c UB , whereas EBook does not—they are misaligned.
Interoperability concerns are addressed in [ 6, 7] via the notion of commitment
alignment. Alignment expresses the intuition that whenever a creditor computes
(that is, infers) a commitment, the presumed debtor also computes the same
commitment. If agents get misaligned, their interaction will potentially break down.