Advanced Semantic Web Policies ____ Preferences and Reactivity

1. Advanced Semantic Web Policies____Preferences and Reactivity Philipp Kärger L3S Research Center, Leibniz University Hannover Research Seminar, DERI Galway, Ireland, July 31st 2008

2. Outline Semantic Web Policies what are they? what do they serve for? Preferences and Policies Why should there be preferences? A Trust Negotiation scenario. Preferences used in two ways for solving the problem Reactive Policies Why should they be reactive? A communication scenario. Combing a reactivity framework and a policy framework

3. Me and the intention of this talk three weeks research visit at DERI This talk should provide you with some background in Semantic Web policies ideas of past and planned research not too many details, rather general for questions, please interrupt! my project context: REWERSE OKKAM TENCompetence

4. What is a policy? In a very broad way, a policy is defined as a statement defining the behaviour of an entity.

5. Policies - Examples “If customers are younger than 26 give a 20% discount on goods subclassing ‘educational item’.” “Up to 15% of network bandwidth can be reserved if payment is done with an accepted credit card” “Move e-mails sent by my FOAF-friends to the folder ‘private’.”

6. Policies are everywhere • Business rules, B2B contracts • e.g. quantity flexible contracts, late delivery penalties • Negotiation • e.g. rules associated with auction mechanisms • Security • e.g. access control policies • Privacy • Information Collection Policies (“ P3P Privacy Policies”) • Workflow management • What to do under different sets of conditions • Context aware computing • Context-sensitive preferences [ by Norman Sadeh, Semantic Web Policy Workshop panel,ISWC 2005 ]

7. Policies on the Semantic Web Build Semantic Web applications/systems/agents where Behaviour can depend on Semantic Web knowledge, that is events, facts, relation between concepts, messages exchanged, etc. e.g., “You can get access if you are a FOAF of mine.”

8. Policies on the Semantic Web: Benefits Reasoning about agent behavior Behaviour can be changed/updated without re-coding, re-compiling, re-installing, etc. in a costless manner Explicit license for autonomous behavior Reusability Extensibility Context-sensitivity Verifiability Support for simple as well as sophisticated agents Protection from poorly-designed, buggy agents

9. Trust Negotiation: Policies in Action request for a book “for the book I need a CreditCard” “for the CreditCard I need a BBB cert.” Alice on-line book shop policy: policy: Disclose Book IFRequestor discloses valid CredidCard Disclose BBB certificate to any requestor Disclose CreditCard IF Requestor has BBB certificate

10. Trust Negotiation: used for … Trust Negotiation is used for Access control Dynamic contracts E.g., in web service composition Autonomic computing Pervasive environments E.g., sensor networks Service-level agreements e.g., more service for certain requestors Etc.

11. Protune – Rule-based Policies on the Semantic Web a policy framework developed at L3S Research Center and Naples University provides a logic-based, declarative policy language features include trust negotiation external actions access to relational databases, RDF stores, file system requests, time and location-aware packages policy explanations “You cannot access because …” (in contrast to just “Access denied.”) • Demo at: http://policy.L3S.uni-hannover.de/

12. Let’s talk about advanced policies … Current Semantic Web policy frameworks miss two important features: Preferences  Reactivity

13. Policies and Preferences What if a policy evaluation has more than one result? request for a book Alice on-line book shop Disclose CreditCard IF Requestor has BBB certificate Disclose bank account information IF Requestor has BBB certificate “for the book I need a CreditCard or your bank account information” Which Credential? CreditCard or bank account information?  exploit user preferences in the negotiation process to decide

14. Preference handling a preference is an order of values having a decreasing preference “I prefer green to red and my last option is brown.” “I prefer English but German is also fine.” preferences are known from: databases: preference queries [Werner Kießling: Preference SQL: design, implementation, experiences. 2002] [Jan Chomicki: Preference formulas in relational queries. 2003] logic programming: preferring answer set [Gerhard Brewka, Thomas Eiter: Preferred Answer Sets for Extended Logic Programs. 1999] 1 2

15. Preferences in Policies - the database approach Idea: exploit user preferences over the credentials: generate all possible next steps in the negotiation and select the optimal step according to these preferences like selecting the optimal entry in a database with a preference query for example{ e-mail, date of birth, passport, credit card } is preferred to { name, ID, bank account } according to the above preferences.

16. Preferences in Policies - the database approach (2) drawbacks of this approach: non-preferred disclosure sets are first created although they will be thrown away later conditional preferences can not depend on arbitrary conditions e.g., “A is preferred to B only if it is sunny in Galway.” preferences are defined on grounded literals (representing credentials) i.e., preference statements with variables are impossible e.g., “X is preferred to Y only if age(X) > age(Y).” Solution: defining the preferences as parts of the policies.

17. Preference and Policies – a log. progr. approach A policy with preferences: If possible: Disclose bank account Otherwise: Disclose credit card IF Requestor has BBB certificate inspired by Answer Set Programming with Ordered Disjunctions: advantage: variables in preferences arbitrary conditions for preferences non-preferred solutions (here answer sets) are not created so far no partial order preferences possible  requires extensions

18. Let’s talk about advanced policies … Current Semantic Web policies miss two important features: Preferences Reactivity 

19. Reactive PoliciesWhile doing valuable research … My students can call me only on Wednesday morning. After the semester, deny their calls. DERI members can only call me during business hours. Always accept files sent by DERI members but only if it’s not an exe file. Show my date of birth only to family members. Automatically accept “share contact dates” for DERI members and for the contacts of my family. Notify me if one of my contacts has birthday and goes online. If someone phones me while I am on a call, deny the call and open a chat instead.

20. Reactive Policies vs. Current Policies Current policies define under which circumstances conditions are true. for example, who exactly gets access why we grant access what is needed to get access

21. Reactive Policies vs. Current Policies But what is missing in current policy frameworks? When is the policy evaluated?  Triggering Events What exactly happens if a policy is evaluated to true or false?  Actions (as reactions to events) IF EVENT “call comes in” HAPPENS AND “I am on another call” HOLDS PERFORM ACTION “deny call and open chat” If someone phones me while I am on a call, deny the call and open a chat instead. Reactivity!

22. Reactive Policies - Applications applications for Reactive Semantic Web Policies: react to changes in the Semantic Web notifications of changes propagation of events and updates automated re-crawling of Semantic Web resources making applications Semantic Web driven (e.g., communication in messengers)

23. Research on Reactivity Reactivity inDatabases: “Active Database Systems”, Book, 1995 many more Reactivity on the web: “An Event Condition Action Language for XML”, WWW2002 EDBT 2006 Workshop “Reactivity on the Web” REWERSE Work Package “Evolution and Reactivity” some more

24. Event Condition Action Policies - inspired by Event Condition Action Rules (ECA rules) always three components: Event: when is the rule evaluated Condition: what has to be satisfied Action: what is the reaction to the event ON a call comes inIF I am on another callDO deny call and open chat If someone phones me while I am on a call, deny the call and open a chat instead.

25. Reactive Policies – An Implementation Idea: Combining a Reactive Framework and a Policy Framework: r³ and Protune

26. Reactive Policiesr3 – Resourceful Reactive Rules r3 – Resourceful Reactive Rules (developed at the AI Center, Universida de Nova de Lisboa (Portugal)) (Semantic) Web Rule Engine for Reactive Rules evaluates rules of the form: <rule> <event>myEventLanguage:SkypeCallComesIn(User)</event> <condition>myConditionLanguage:isNotTrusted(User)</condition> <action>myActionLanguage:denyCall(User)</action> </rule> plugging in arbitrary languages makes it really flexible

27. Reactive Policies - Combining r3 and Protune any event language (e.g., XChange, Prova) Protune goals • <rule> • <event>myEventLanguage:SkypeCallComesIn(User)</event> • <condition>PROTUNE:isNotTrusted(User)</condition> • <action>PROTUNE:denyCall(User)</action> • </rule> Protune external actions L3S Research Seminar

28. Reactive Policies - Benefits enhance reactivity with policies • Protune • allows for negotiations, information exchange • provides explanations • allows for (external) actions • r³ • allows for arbitrary event languages • evaluates Event Condition Action rules • handles the binding across events, conditions, actions making policies reactive

29. Summary Semantic Web Policies used to define automated behavior Policies in action: Trust Negotiation a Semantic Web policy framework: Protune Preferences in Policies needed for adequate representation of user intention two approaches inspired by Databases and Log. Progr. ECA policies enhance policies with events and actions needed for many Semantic Web applications combining r³ and Protune merges policies and reactivity L3S Research Seminar

30. Thank you for your attention. Please let me know if there are any questions. Philipp Kärger kaerger@L3S.de http://www.L3S.de/~kaerger