Retractability, games and orchestrators for session contracts

TL;DR

This paper introduces affectible session contracts that model adaptable client/server interactions, providing a game-theoretic framework and establishing equivalences with orchestrator-mediated compliance and rollback-based interactions.

Contribution

It extends session contracts to include affectible outputs, defines affectible compliance with a game-theoretic interpretation, and links winning strategies to orchestrators.

Findings

Affectible compliance has a three-party game interpretation.

Effective correspondence between winning strategies and orchestrators.

Subcontract relations for affectible contracts are characterized.

Abstract

Session contracts is a formalism enabling to investigate client/server interaction protocols and to interpret session types. We extend session contracts in order to represent outputs whose actual sending in an interaction depends on a third party or on a mutual agreement between the partners. Such contracts are hence adaptable, or as we say "affectible". In client/server systems, in general, compliance stands for the satisfaction of all client's requests by the server. We define an abstract notion of "affectible compliance" and show it to have a precise three-party game-theoretic interpretation. This in turn is shown to be equivalent to a compliance based on interactions that can undergo a sequence of failures and rollbacks, as well as to a compliance based on interactions which can be mediated by an orchestrator. Besides, there is a one-to-one effective correspondence between winning strategies and orchestrators. The relation of subcontract for affectible contracts is also investigated.