A Framework for Contractual Resource Sharing in Coalitions

1. A Framework for Contractual Resource Sharing in Coalitions Babak Sadighi Firozabai (SICS), Marek Sergot (IC), Anna Squicciarini (UoM) and Elisa Bertino (UoM)

2. Overview • Coalition: heterogeneous and independently managed enterprises collaborating to achieve a common goal • Sharing resources may be part of the collaboration • No single line of authority dictating how resources can be shared among the coalition members • Resource sharing is regulated by a contract between coalition members Policy 2004

3. Overview • Resources are managed locally and released upon requests • A coalition policy (contract) specifies obligations of coalition members to share their resources among them • An enterprise is a member of a coalition only if it agrees to follow the coalition contract • A Local policy (or a plan) specifies when and under what conditions a coalition member allows use of its resources by other coalition members • Members publish their local policies within the coalition Policy 2004

4. Coalition Policy (Contract) • Example: • Each member of the coalition is obliged to provide 10GB of disc-space, for two hours a day, to all other members of the coalition. • Enterprise E1 is obliged towards E2 to provide access to application Aup to 3 hours, each working day. Policy 2004

5. Local Policy of E1 • Example: • 10GB of disc-space will be provided to other members but only between 8-10 pm. • Employees of E2 are entitled to access application A for four hours starting at any time during working hours. Policy 2004

6. Coalition Policy R R R R R R R R R C C R R R Overview Two independent enterprisesE1andE2 Policy 2004

7. Check Request Request Overview • Access Request Procedure Coalition Policy C C R R R R R R R R R R R R Policy 2004

8. Overview • Each party must publish a local policy complying with the coalition contract • Parties are not, in practice, forced to follow their local policies (plans) • A party may choose to not grant a request although it has promised it in its local policy • An enterprise may be member of several coalitions and as the result it may have promised access to its resources more than what it can answer Policy 2004

9. Overview • Obligation as a deontic concept • Obligations can be violated • Entitlement as strong permission • If X is entitled to access A, then Y (the controller of A) is obliged to grant X’s request for accessing A • Denying an entitled request is regarded as violation of corresponding obligation • Publishing an entitlement in a local policy is regarded as an obligation (a promise) by the publisher to the entitled agent Policy 2004

10. Overview • Local policies may change • A coalition member may change its promises as time passes based on how its resources are actually used • Changing local policy is a way of scheduling and optimising resource usage • Contracts do not change • In current version of the framework we do not allow changes of contractual terms during coalition life-time Policy 2004

11. The Framework • Coalition elements • Set of resources shared among coalition members • Set of users of the coalition resources • Finite set of enterprises that are coalition members • Set of policies of a coalition, namely the coalition policy (the contract) and the set of local policies of the members (LPtEi) • Two basic policy components: Obligation and entitlement Policy 2004

12. The Framework • Resources • A generic specification of resources based on the following metrics • Time (e.g. (22-09-2003,13:54:23) • Scalar (some suitable numeric value) • Max limit – Min limit (limits on the given metrics) • Generic resource comparison • R1is-less-than R2. R1 and R2 must be of the same type. Policy 2004

13. The Framework • Obl(P,S,R,I) where • P is the enterprise that is the bearer of the obligation • S is the set of enterprises to whom the obligation is owed • R is the specified amount of a resource • I = [ts, te] is the validity time-period of the obligation Policy 2004

14. The Framework • EntA(E, R, I) • A is the issuer of the entitlement • Eis the set of entitled enterprises • R is the promised resource by A • I is the validity time-period of the entitlement • An entitlement is regarded as an obligation of A to grant access to R upon requests from employees of enterprises E • Promises are obligations which means that they may get violated Policy 2004

15. The Framework • Local Policy (LP) is a finite set of entitlements • A local policy is in compliance with (meets) an obligation at time t • LPP meets Obl(P, S, R, I) iff • There is a set of entitlements that covers I and R, and • t  I • At each time point of a coalition life-time, each coalition member must have (published) a local policy that meets its obligations stated in the coalition contract. Policy 2004

16. The Framework • Supported request • Req(u, P, R, t) is supported if there is an Obl(P, S, R’, I) if • tI, and • uis an employee of an enterprise belonging to S, and • Ris-less-thanR’ • Locally supported request • Req(u, P, R, t) is supported by a local policy if there is an entitlement supporting it Policy 2004

17. The Framework • An obligation Obl(P,S,R,I) is violated at time t  I if • there is no local policy that meets it at time t,or • a request supported by it is not granted. • Otherwise the obligation is fulfilled if t is after I • An obligation is fulfilled if no supported request is submitted • ”use-it-or-loose-it” principle Policy 2004

18. The Framework • Contract • Contract blocks • Obligation sequences • Obligations • Obligation sequence Obl(P, S, (R1, I1); (R2, I2);…; (Rn, In)) • R1,R2,…,Rn are all of the same type • I1,I2,…In is an ordered sequence of contiguous time • An obligation sequence is violated at time t if any of its constituent obligations is violated at t. • A local policy is in compliance with an obligation sequence at time t if every constituent obligation is either fulfilled at t or the local policy meets it at time t. Policy 2004

19. The Framework • A contract block is an expression of the form: obl(P, S1; Seq1)|| … ||obl(P, Sn; Seqn) • P is the bearer of the obligations in the block • A contract block is fulfilled at time t iff any of its obligation sequence is fulfilled at time t. • A contract block is violated at time t if all its obligation sequences are violated at t. Policy 2004

20. The Framework • The idea of contract block is to give a free choice to the bearer about which of the obligation sequences it wants to fulfil. • In practice, contract blocks can be used to specify obligations which violation of one results in activation of a more stricter obligation to be fulfilled. • Contract blocks are the way we define violation punishments and sanctioning mechanisms in our framework. • Note that an enterprise choose among the obligation sequences of a contract block by specifying an entitlement in its local policy that meets that specific obligation sequence. Policy 2004

21. The Framework • Finally: • A contract is a finite set of contract blocks. • A contract is fulfilled at time t if all its contract blocks are fulfilled at time t. • A contract is violated at time t if any of its contract blocks is violated at time t. Policy 2004

22. Future work • An architecture for contractual performance monitoring • A more elaborated resource description language • Use of the framework for resource optimisation and automatic resource-usage scheduling • Mechanisms to decide which obligations to fulfil in order to maximize resource usage and minimize sanctioning costs • Relations to other ongoing work on contracts and service level agreements such as Web Service Level Agreement (WSLA) Policy 2004

23. Questions? Policy 2004