A toolkit for model checking of electronic contracts

Abstract

In the business world, contracts are used to regulate business interactions between trading parties. In this context, an electronic contracting systems can be used to monitor business–to–business interactions to ensure that they comply with the rights (permissions), obligations and prohibitions stipulated in contract clauses. Such an electronic contracting system will require an executable version of the contract (e-contract) for compliance checking. It is important to be verify the correctness properties of an e- contract before deploying it for compliance checking. Model checkers are widely used for automatic verification of concurrent systems. However, such tools for e-contracts with means for expressing directly and intu- itively key concepts that appear recurrently in contracts, such as execu- tions of business operations, granting (cancellation, suspension, fulfilment, violation, etc.) of rights, obligations and prohibitions to role players are not yet available. This thesis rectifies the situation by developing a high-level e-contract verification toolkit using the Spin model checker. A formal Contractual Business-To-Business interaction (CB2B) model based on the concepts of contract compliance checking developed earlier at Newcastle university has been constructed. Further, Promela, the input language of the Spin model checker, has been extended in a manner that enables specification of contract clauses in terms of contract entities: role players, business operations, rights, obligations and prohibitions. A given contract can now be expressed using extended Promela as a set of declarations and a set of Event-Condition-Action rules. In addition, the designer can specify the correctness requirements to be verified in Linear-Temporal-Logic directly in terms of the contract entities. A notable feature is that the CB2B model automatically checks for contract independent properties: properties that must hold for all contracts. For example, at run time, a contract should not simultaneously grant a role player a right to perform an operation and also prohibit it. Thus, the toolkit hides much of the intricate details of dealing with Promela processes communicating through channels and enables a designer to build verifiable abstract models directly in terms of contract entities. The usefulness of the toolkit is demonstrated by trying out a number of contract examples used by researchers working on contract verification. The thesis also shows how the toolkit can be used for generating test cases for testing an implemented system.