Choreographies in the wild

Abstract

We investigate the use of choreographies in distributed scenarios where, as in the real world, mutually distrusting (and possibly dishonest) participants may be unfaithful to their expected behaviour. In our model, each participant advertises its promised behaviour as a contract. Participants may interact through multiparty sessions, created when their contracts allow to synthesise a choreography. We show that systems of honest participants (which always adhere to their contracts) enjoy progress and session fidelity.

Honesty by Typing

“…The concept of contract-oriented computing (as surveyed in Section 1) has been introduced in [14], and CO 2 has been later proposed as a contract-agnostic calculus for contract-oriented computing in [12]. CO 2 has been instantiated with several contract models -both binary [13,10,9] and multiparty [12,36,8]. Here, similarly to [9], we consider bilateral contracts, formalised as binary session types (Section 2).…”

“…Coherently, the main property we are interested in is honesty, which is a property of components, and not of global applications. Some works mixing top-down and bottom-up composition have been proposed in the past few years [26,37,36,8].…”

“…(2) when C B is stipulated, the buyer chooses apples (buyA) or bananas (buyB); (3) if the buyer chooses apples, S gets the payment (pay1E), and ships the item (shipA); (4) otherwise, if the buyer chooses bananas, S checks if the item is in stock; (5) if bananas are in stock, S provides the buyer with the quotation of 1 (quote1E), receives the payment (pay1E), and ships the item (shipB); (6) otherwise, if bananas are not in stock, S advertises the contract C D ; (7) when C D is stipulated, S pre-orders bananas from the distributor (buyB); (8) S sends a 3 quotation to the buyer (quote3E) and waits for the buyer's reply; (9) if the buyer pays 3 (pay3E), then S pays the distributor (pay2E), receives the item from the distributor (shipB), and ships it to the buyer (shipB). The store service terminates correctly whenever two conditions hold: the buyer is honest, and at step 7 the middleware selects an honest distributor.…”

Contracts as games on event structures

“…In the case a violation is found, the judge will eventually provide the prescribed compensations/punishments. Some formal models for contract-oriented computing have been proposed, using as contracts logical formulae [14], process algebras [17], binary [29], and multi-party session types [30]. Since honesty is undecidable [29], some papers have addressed the problem of devising verification techniques to safely overapproximate it [31,32].…”

“…Some formal models for contract-oriented computing have been proposed, using as contracts logical formulae [14], process algebras [17], binary [29], and multi-party session types [30]. Since honesty is undecidable [29], some papers have addressed the problem of devising verification techniques to safely overapproximate it [31,32]. In the setting of contract-oriented computing, the notion of protection studied in this paper addresses the issue of providing participants with non-losing strategies when the contract broker establishes sessions in the absence of an agreement.…”