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

2. 20040608Policy 2004 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

3. 20040608Policy 2004 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

4. 20040608Policy 2004 Coalition Policy (Contract) Example: 1. 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. 2. Enterprise E 1 is obliged towards E 2 to provide access to application A up to 3 hours, each working day.

5. 20040608Policy 2004 Local Policy of E 1 Example: 1. 10GB of disc-space will be provided to other members but only between 8-10 pm. 2. Employees of E 2 are entitled to access application A for four hours starting at any time during working hours.

6. 20040608Policy 2004 Overview Two independent enterprises E 1 and E 2 R R R R R R R R R RR R CC Coalition Policy

7. 20040608Policy 2004 Overview Access Request Procedure R R R R R R R R R RR R CC Coalition Policy Request Check

8. 20040608Policy 2004 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

9. 20040608Policy 2004 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

10. 20040608Policy 2004 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

11. 20040608Policy 2004 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 (LP t Ei ) Two basic policy components: Obligation and entitlement

12. 20040608Policy 2004 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 R 1 is-less-than R 2. R 1 and R 2 must be of the same type.

13. 20040608Policy 2004 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 = [t s, t e ] is the validity time-period of the obligation

14. 20040608Policy 2004 The Framework Ent A (E, R, I) A is the issuer of the entitlement E is 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

15. 20040608Policy 2004 The Framework Local Policy (LP) is a finite set of entitlements A local policy is in compliance with (meets) an obligation at time t LP P 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.

16. 20040608Policy 2004 The Framework Supported request Req(u, P, R, t) is supported if there is an Obl(P, S, R’, I) if t  I, and u is an employee of an enterprise belonging to S, and R is-less-than R’ Locally supported request Req(u, P, R, t) is supported by a local policy if there is an entitlement supporting it

17. 20040608Policy 2004 The Framework An obligation Obl(P,S,R,I) is violated at time t  I if 1. there is no local policy that meets it at time t, or 2. 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

18. 20040608Policy 2004 The Framework Contract Contract blocks Obligation sequences Obligations Obligation sequence Obl(P, S, (R 1, I 1 ); (R 2, I 2 );…; (R n, I n )) R 1,R 2,…,R n are all of the same type I 1,I 2,…I n 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.

19. 20040608Policy 2004 The Framework A contract block is an expression of the form: obl(P, S 1 ; Seq 1 ) || … || obl(P, S n ; Seq n ) 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.

20. 20040608Policy 2004 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.

21. 20040608Policy 2004 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.

22. 20040608Policy 2004 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)

23. 20040608Policy 2004 Questions?