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The Policy-Aware Web: Privacy and Transparency on the Semantic Web

The Policy-Aware Web: Privacy and Transparency on the Semantic Web. Jim Hendler Hendler@cs.umd.edu http://www.cs.umd.edu/~hendler. 2004 NSF National Priorities ITR to UMCP and MIT (Hendler, Berners-Lee, Weitzner- PIs). Access and Privacy Control.

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The Policy-Aware Web: Privacy and Transparency on the Semantic Web

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  1. The Policy-Aware Web: Privacy and Transparency on the Semantic Web Jim Hendler Hendler@cs.umd.edu http://www.cs.umd.edu/~hendler 2004 NSF National Priorities ITR to UMCP and MIT(Hendler, Berners-Lee, Weitzner- PIs)

  2. Access and Privacy Control

  3. As we publish more info- how do we control access … Who can see What??

  4. Current Policy Languages • A number of languages being explored: • P3P (data-centric relational semantics -> relational database) • WS-Policy (propositional, and & or, but weak not) • Features and Properties (no operators, easier to map to RDF) • Combinators (choose one/all, similar to WS-Policy) • KaOS Policy and Domain Services • WSPL and EPAL (subsets of XACMLs) • XACML (and, or, not, first and higher order bag functions) • Rei (OWL-Lite + logic-like variables) • A lot of ambiguity about exact expressivity and computational properties (or even the semantics!)

  5. An example: WS-Policy • WS-Policy provides a flexible grammar for expressing C&C of web services • Normalized form (maybe to do non normalized) • Two translation approaches: • Policies as Instances • Readable, but hard to capture semantics • Available at: http://mindswap.org/dav/ontologies/ws-policy_instance.owl • Policies as Classes • Translate WS-Policy constructs into OWL constructs • E.g., wsp:All --> owl:intersectionOf

  6. WS-Policy Example <wsp:Policy> <wsp:ExactlyOne> <wsp:All> <wsse:SecurityToken> <wsse:TokenType>wsse:Kerberosv5TGT</wsse:TokenType> </wsse:SecurityToken> </wsp:All> <wsp:All> <wsse:SecurityToken> <wsse:TokenType>wsse:X509v3</wsse:TokenType> </wsse:SecurityToken> </wsp:All> <wsp:All> <wsse:SecurityToken> <wsse:TokenType>wsse:UserNameToken</wsse:TokenType> </wsse:SecurityToken> </wsp:All> </wsp:ExactlyOne> </wsp:Policy>

  7. Mapping WS-Policy to OWL • “all” is easy: it’s logical conjuction (i.e., intersectionOf) • “exactlyOne” is harder, two readings: • Older version: “oneOrMore” • Inclusive OR, maps to owl:unionOf • “exactlyOne” suggests XOR • Have to map to a disjunction of conjunctions • Quadratic increase in size of disjuncts • Ontology: http://www.mindswap.org/dav/ontologies/policytest.owl

  8. Example • @prefix owl: <http://www.w3.org/2002/07/owl#> .@prefix policytest: <http://www.mindswap.org/~kolovski/policytest.owl#> .policytest:TestPolicyaowl:Class;owl:intersectionOf     ( owl:unionOf     ( policytest:SecurityTokenTypeUsernameTokenpolicytest:SecurityTokenTypeX509policytest:SecurityTokenTypeKerberos ) owl:complementOfowl:unionOf     ( owl:intersectionOf     ( policytest:SecurityTokenTypeUsernameTokenpolicytest:SecurityTokenTypeX509 ) owl:intersectionOf     ( policytest:SecurityTokenTypeUsernameTokenpolicytest:SecurityTokenTypeKerberos ) owl:intersectionOf     ( policytest:SecurityTokenTypeX509policytest:SecurityTokenTypeKerberos )  )    )  .

  9. Use OWL tools

  10. Policy Aware WEB (NSF ITR; Hendler, Berners-Lee, Weitzner; 2005)

  11. PAW demo…

  12. Use case: A Web browser requests the home page for a girl scout troop and is given it by a Web server. Web Server Content Demo

  13. However, requests for images result in HTTP Error 401, “Unauthorized” Web Server 401 Content 401

  14. The 401 “Unauthorized” response has been modified to provide a URL to a policy: HTTP/1.1 401 Not authorized Date: Sat, 03 Dec 2005 15:32:18 GMT Server: TwistedWeb/2.0.1 Policy: http://groups.csail.mit.edu/dig/2005/09/rein/examples/troop42-policy.n3 Content-type: text/html; charset=UTF-8 Connection: close 10:32:20 ERROR 401: Not authorized. Demo

  15. Example policies Photos taken at meetings of the troop can be shared with any current member of the troop. Photos taken at a jamboree can be shared with anyone in the troop or with anyone who attended the jamboree. Photos of any girl in the troop can be shared with the world if that girl's parent has given permission Policies use linked rules { REQ a rein:Request. REQ rein:resource PHOTO. ?F a TroopStuff; log:includes { PHOTO a t:Photo; t:location LOC. LOC a t:Meeting }. REQ rein:requester WHO. WHO session:secret ?S. ?S crypto:md5 TXT. ?F a TroopStuff; log:includes { [] t:member [ is foaf:maker of PG ]. LOC t:attendee [ is foaf:maker of PG ] }. PG log:semantics [ log:includes { PG foaf:maker [ session:hexdigest TXT ] } ]. } => { WHO http:can-get PHOTO }.

  16. Rein "ontology"

  17. Rein example { <http://dig.csail.mit.edu/2005/09/rein/examples/troop42.rdf> log:semantics ?F } => { ?F a TroopStuff }. # Photos take at meetings of the troop can be shared with any # current member of the troop { REQ a rein:Request. REQ rein:resource PHOTO. ?F a TroopStuff; log:includes { PHOTO a t:Photo; t:location LOC. LOC a t:Meeting }. REQ rein:requester WHO. WHO session:secret ?S. ?S crypto:md5 TXT. ?F a TroopStuff; log:includes { [] t:member [ is foaf:maker of PG ]. LOC t:attendee [ is foaf:maker of PG ] }. PG log:semantics [ log:includes { PG foaf:maker [ session:hexdigest TXT ] } ]. } => { WHO http:can-get PHOTO }. # Photos taken at a jamboree can be shared with anyone in the # troop or with anyone who attended the jamboree. # (i) anyone who is in the troop { REQ a rein:Request. REQ rein:resource PHOTO. ?F a TroopStuff; log:includes { PHOTO a t:Photo; t:location LOC. LOC a t:Jamboree }. REQ rein:requester WHO. WHO session:secret ?S. ?S crypto:md5 TXT. ?F a TroopStuff; log:includes { [] t:member [ is foaf:maker of PG ]. }. PG log:semantics [ log:includes { PG foaf:maker [ session:hexdigest TXT ] } ]. } => { WHO http:can-get PHOTO }. # (ii) anyone who attended the jamboree { REQ a rein:Request. REQ rein:resource PHOTO. ?F a TroopStuff; log:includes { PHOTO a t:Photo; t:location LOC. LOC a t:Jamboree }. REQ rein:requester WHO. WHO session:secret ?S. ?S crypto:md5 TXT. ?F a TroopStuff; log:includes { LOC t:attendee [ is foaf:maker of PG ]. }. PG log:semantics [ log:includes { PG foaf:maker [ session:hexdigest TXT ] } ]. } => { WHO http:can-get PHOTO }. The RDF/XML syntax is even worse: Authorability/Editability are important issues Specialized use (cf. Creative Commons) a partial out.

  18. Use of the PAW proof-generation proxy results in a proof which satisfies the policy: Web Server Proof Third-party services may be consulted to help construct the proof. Demo

  19. The proxy: Uses Rein, a policy engine, to specify rules which match a given policy. The Rein rules are run in Cwm, a forward-chaining reasoner for the Semantic Web. This generates a proof. Proof is HTTP-PUT on the server, and a HTTP-GET on same document is then invoked (requires HTTP 1.1) Demo

  20. The Web server checks the proof and serves the content if it is valid. Web Server Content Demo

  21. The server: Uses Cwm to validate the proof. Takes action based on validation (serves content or denies). Demo

  22. Current demo work: Get it working - Fix cwm proof generation (log:supports?) Make use of multiple distributed authentication systems (instead of holding secrets in the proxy). Associate content with RDF metadata and base policy decisions on the RDF (cf. policy 3) Address issues of eventual integration of the proxy with a Web browser (e.g. cookie storage). Extend system to "distributed" scenarios (different authorities hold parts of policy, may have own rules on access) Demo

  23. Open, Distributed Rules Challenges • Common Notation • "Small matter of standardization" • N3, SWRL, RuleML • Identity vs. privacy • How do you identify yourself w/o violating the very privacy concerns we hope to address? • Current identity schemes are centralized and universal • Can we do a distributed ID model (maybe email based)? • Inconsistency • In logic "P ^ -P => Q" • On Web it better not! (Supported(Bush) ^ --Supported(Bush)) => you owe me $1000 • Can we use a "non-standard" logic solution?

  24. Another Cool thing… • What is a rule of logic? • In traditional philosophy it relates to "Truth" • What is truth on the Web? • Ex: How many cows are in Texas? • On the Web, we could use an idea of agreed upon rules, grounded at URI • Social definition of truth via shared contexts • Ex: Because Mom said so…

  25. Conclusions • Information lives in specific contexts • The Semantic Web helps us place information into these (multiple) contexts. • Control of information requires control of contexts • Explication of policies • Linked in a Web-like way • Integrated directly into the Web • With extensions for rules and proofs • Is really hard • Issues of identity, inconsistency, grouding, change over time • But holds great potential • Personal Control of your information spaces • "Policy-Aware" Web project (joint between UMCP and MIT) • Goal: make this real! http://www.mindswap.org/~hendler/2004/PAW.html

  26. backup

  27. Truth on Web Pages [based on Heflin etal, 1998] • Inference rules could be used to determine the credibility of claims • I might believe the claims made by a reliable Newspaper • Trustable(x) :- x; reliableNewspaper. • And I could establish the Washington Post as reliable... • i.e. I assert: http://www.washingtonpost.com owl:class reliableNewspaper. • or if I infer it • ReliableNewspaper(X) :-> X owl:class ReliableNewspaper;http://MediaWatchList. • (?) reliableNewspaper(X) :- X owl:class ReliableNewspaper; src ^ trusted(src). • The rules are "grounded" in a testable way • cf. If I can HTTP-get the fact, then it is asserted

  28. Rule Sets could be shared • You can ground your sources • X :- X; src ^ src owl:class TrustedSource; http://…/myMomSet.rdf • Or infer trusted sources based on other rule sets • X :- X; src ^ src owl:class TrustedSource; http://ex.com/RushLimbaughSet.rdf • X :- X; src ^ src owl:class TrustedSource; http://ex.com/UnabomberRules.rdf ^ --( X;http://www.rushLimbaugh.com/truths.rdf)

  29. Annotated Logic(in 25 words or less) • Traditional Logic P & -P => Q (P and -P are inconsistent) • Annotated Logic • P;X & -P;Y are not inconsistent • P;X & -P;X => Q;X but not Q;Y • P;X & -(P;X) is inconsistent and must be avoided (but this is easily checked if inference of RHS is restricted)

  30. On the Web • Annotations represent document contexts X;Y and -(X;Y) cannot co-occur (unless Web is broken) (modulo temporal change, but that's another talk) <foaf:Person> <foaf:name>Jim Hendler</foaf:name> <foaf:title>Dr</foaf:title> <foaf:firstName>Jim</foaf:firstName> <foaf:surname>Hendler</foaf:surname> <foaf:mbox_sha1sum> be972c7a602683f7cf3c7a1fd0949c565debe4d3 </foaf:mbox_sha1sum> <foaf:homepage rdf:resource="http://www.cs.umd.edu/~hendler"/> <foaf:depiction rdf:resource="http://www.semanticgrid.org/q-iantbljim.jpg"/> <foaf:workplaceHomepage rdf:resource="http://owl.mindswap.org"/> </foaf:Person> <foaf:name>Jim Hendler</foaf:name> ; http://www.cs.umd.edu/~hendler/2003/foaf.rdf == http://www.cs.umd.edu/~hendler/2003/foaf.rdf

  31. "Because it's there…"

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