On the Realizability of Contracts in Dishonest Systems

Abstract

Abstract. We develop a theory of contracting systems, where behavioural contracts may be violated by dishonest participants after they have been agreed upon -unlike in traditional approaches based on behavioural types. We consider the contracts of [10], and we embed them in a calculus that allows distributed participants to advertise contracts, reach agreements, query the fulfilment of contracts, and realise them (or choose not to). Our contract theory makes explicit who is culpable at each step of a computation. A participant is honest in a given context S when she is not culpable in each possible interaction with S. Our main result is a sufficient criterion for classifying a participant as honest in all possible contexts.

Choreographies in the wild

“…In this section we discuss the notion of honesty [11], providing several examples. Intuitively, a participant is honest when it is always able to fulfil its contractual obligations, in any context, no matter what other participants do.…”

“…Example 5.2 below). Note that Definition 5.1 above extends the notion of ready set in [11] (where only bilateral sessions are considered) to suit our multiparty contract model. We have CRS(c A ) = {{(B 1 , req)}}: in other words, at this point of the contract, an interaction is expected between A and B 1 (since A is waiting for req), while no interaction is expected between A and B 2 .…”

“…The calculus was then generalised in [22,14] to suit different contract models (e.g., contracts as processes or logic formulae). In [11], it has been instantiated to a theory of bilateral contracts inspired by [23]. The main differences between our adaptation of CO 2 and the original presentation in [22] lie in the specification of session establishment and the introduction of participant variables.…”

“…To overcome the state of nature, and move towards the "social contract" (as in Hobbes' Leviathan), some recent works have proposed to discipline the interaction of services through contracts [10,11]. The idea is a contract-oriented, bottom-up composition, where only those services with compliant contracts can establish sessions through which they interact.…”

“…a system gets stuck, it is always possible to identify which participants violated their contracts. We then adapt the notion of honesty of [11]. We show that an honest service is always able to satisfy its contracts by firing some of its actions, even when the other services do not cooperate (Theorem 6.1).…”