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1 Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer The Sematic Web Trust Layer Jeremy Carroll, Hewlett-Packard Labs, UK Chris Bizer, Freie Universität Berlin, Germany Joint work with Pat Hayes, IHMC, USA Patrick Stickler, Nokia, Finland WWW 2004, New York Developers Day, 22 May 2004 Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Central Questions for the Semantic Web How trustworthy is information found on the Semantic Web? How do I decide that it is trustworthy? 2 Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Agenda 1. Introduction Basic Roles Trust Mechanisms Requirements for a Semantic Web Trust Layer 2. Publishing Information on the Semantic Web Named Graphs Semantic Web Publishing Vocabulary 3. Trusting Information found on the Semantic Web Example Trust Policies Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Basic Roles Information Providers want that their information is used / believed might want to state their publishing intend (assertion, quote) are only willing to put a certain effort into publishing Information Consumers want to use the information for different tasks have different views of the world have different subjective trust requirements have different subjective preferences for certain trust mechanisms 3 Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Trust Policies We are using a wide range of different trust policies in everyday life: We might trust Andy on restaurants but not on computers, buy only from sellers on eBay who have more than 100 positive ratings, regard literature as irrelevant, when it is older than 5 years, trust professors on their research field, believe foreign news only when they are reported by several independent sources. Goal: Allow a similar wide range of trust policies on the Semantic Web. Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Trust Situation on the Semantic Web 4 Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Trust Mechanisms Reputation-based Trust Mechanisms Context-based Trust Mechanisms Content-based Trust Mechanisms Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Reputation-Based Trust Mechanisms include rating systems and web-of-trust mechanisms are a well researched area have a general problem: They require explicit and topic-specific trust ratings high effort for information consumers 5 Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Context-Based Trust Mechanisms use background information about the information provider e.g. his role in the application domain or his membership in a specific group example policies: "Distrust everything a vendor says about his competitor“ or “Trust all members of organization A.” Information created in the information gathering process publishing and retrieval date and the retrieval URL information whether a signature is verifiable or not example policy: “Trust all information which has been signed and is not older than a month.” Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Content-Based Trust Mechanisms use information content itself, together related information content published by other information providers. Example policies: “Believe information which has been stated by at least 5 independent sources.” “Distrust product prices that are more than 50% below the average price.” “Distrust people claiming that Texan cows are aliens.” 6 Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Requirements for a Semantic Web Trust Layer Support different types of warranties Use of all trust relevant information available: Journalism’s WWWWW: who, what, where, when and why Support different, subjective, task-specific trust policies Reputation-based Context-based Content-based Keep in mind that many applications don’t require total trustworthiness. Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Named Graphs - Motivation <rdf:RDF> ... </rdf:RDF> eg:graph1<rdf:RDF> ... </rdf:RDF> eg :g ra ph 2 <rdf:RDF> ... </rdf:RDF> eg:graph3 Make Naming Explicit 7 Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Named Graphs – Abstract Syntax N = (N, V, U, B, L ) V = U ∪ B ∪ L, URIs, blank nodes and literals N is a partial function - domain U - range RDF graphs (sets of triples from V x U x V) - alternatively a set of pairs – each pair being a named graph For a named graph ng = ( n, g ) name(ng) = n rdfgraph(ng) = g Blank nodes not shared between different graphs in N Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Named Graphs – Semantics For every ng = ( n, g ) in N I(n) = ng in an RDF interpretation I which conforms with a collection of named graphs N - Semantic Extension in terms of RDF Semantics class rdfg:Graph properties rdfg:equivalentGraph rdfg:subGraphOf technical detail considering blank node names 8 Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Named Graphs – Semantics 2 A collection of named graphs N is not given a single semantics Semantics determined by set A of uris of accepted graphs. Semantics of N with respect to A is RDF semantics of ∪{ rdfgraph(N(a)) : a ∈ A} Thus 2|N| different meanings Trust is the problem of determining A Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Named Graphs - Syntax RDF/XML TriX (HPL-2004-56, with Patrick Stickler) TriG (based on Turtle subset of N3) :G1 { _:Monica ex:name "Monica Murphy" . _:Monica ex:email <mailto:monica@murphy.org>. :G1 pr:disallowedUsage pr:Marketing } :G2 { :G1 ex:author :Chris . :G1 ex:date "2003-09-03"^^xsd:date } 9 Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Semantic Web Publishing Determining which graphs we trust depends on WWWWW: who, what, where, when and how named graphs are the hooks on which we pin: who, where, when and how. Graph itself answers what. new SWP vocabulary allows for who, how (either signed or unassigned; asserted or quoted) DC usable for where, and when bootstrapping issue for what, and self-describing graphs the meaning of the graph is given by the RDF Semantics, which means we have to (provisionally) accept the graph to determine whether to accept it. Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Semantic Web Publishing - Vocabulary who? how? how? 10 Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Semantic Web Publishing - Example :G1 { :Monica ex:name "Monica Murphy" . :G1 swp:assertedBy _:w1 . _:w1 swp:authority _:a . _:a foaf:mbox <mailto:chris@bizer.de> } :G2 { :G1 swp:quotedBy _:w2 _:w2 swp:signatureMethod swp:std-method-A^^xsd:anyURI . _:w2 swp:signature "..."^^xsd:base64Binary . _:w2 swp:authority _:s . _:s swp:certificate "..."^^xsd:base64Binary . _:s foaf:mbox <mailto:patrick.stickler@nokia.com> . :G2 swp:assertedBy _:w3 . _:w3 swp:signatureMethod swp:std-method-A^^xsd:anyURI . _:w3 swp:authority _:s . _:w3 swp:signature "..."^^xsd:base64Binary } Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Example Policies First one now, then some formal semantics, then Chris presents another 11 Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Example 1: Knowledge Base Integration Policy: Believe everything that has been explicitly asserted and signed, while maintaining a consistent knowledge base. Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Algorithm (non-deterministic and lazy) K is initial KB (possibly empty or not) 1. Set A := {} 2. Non-deterministically choose n ∈ domain(N) − A, or terminate. 3. Set K0 := K ∪ N(n), provisionally assuming N(n). (Bootstrapping) 4. If K0 is inconsistent then backtrack to 2. 5. Evaluate query on OWL closure K0: SELECT ?certificate ?method ?sign WHERE ( n swp:assertedBy ?w1 . ?w1 swp:authority ?s . ?w1 swp:signatureMethod ?method . ?w1 swp:signature ?sign ) ( ?s swp:certificate ?certificate ) 6. If ?certificate is OK, and ?sign is a signature according to ?method using ?certificate, then set K := K0 and A := A ∪ {n}, otherwise backtrack to 2. 7. Repeat from 2. Step 4 should be evaluated lazily. Step 6 could check that authority is trusted. 12 Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Bootstrapping: Wittgenstein – On Certainty (as presented by Gerd Brand: The Central Texts of Wittgenstein) Doubt only exists as doubting conduct. I cannot live with doubting conduct alone. On the contrary, my normal life is for the most part a non-doubting conduct. [...] doubting behaviour exists only by reason of a non-doubting behaviour, [...] at the beginning stands not-doubting. Because doubt rests on what cannot be doubted [...] I cannot arrive at a genuine doubt as long as I want to doubt everything, A doubt without end is not even a doubt, just as to want to doubt everything means not even coming to doubt. Wittgenstein: “There are cases where doubt is unreasonable, but others where it seems logically impossible. And there seems no clear boundary between them.” (OC 454) Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Semantics of Signatures Extension of RDF Semantics adds legal persons and their agents to domain of discourse interpretation of swp:certificate restricted by identifying information in certificates interpretation of swp:signature restricted by the signature method applied to the asserted or quoted graph with the certificate of the authority. Note certificate validity not checked at this stage, but is part of trust policy details in paper (credit Hayes and Carroll) 13 Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Self-Asserting Graphs as Performatives :G1 { :Monica ex:name "Monica Murphy" . :G1 swp:assertedBy _:w1 . _:w1 swp:authority _:a . _:a foaf:mbox <mailto:chris@bizer.de> } Performatives: e.g. “I do”, “I promise to pay ...” Asymmetric semantics: means more to first person, (as social convention). When Chris interprets :G1 then it is necessarily true, (subject to signatures or other verification) Other people might not trust Chris Details in paper (Hayes) Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Example 2: The TriQL.P Trust Architecture TriQL.P is a query language, that allows the formulation of trust policies within queries similar to RDQL uses graph patterns supports set operations and different ranking mechanisms returns justification trees together with the query results Justification trees provide explanations why data should be trusted can be used to implement Tim Berners- Lee’s “Oh, yeah?” button. 14 Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Architecture Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Example Application domain: Skill management Query: Retrieve all persons with the skill "Programming“. Query specific, context-based Trust Policy: Use only claims by people who have an affiliation to at least 2 projects involving “Programming”. 15 Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer TriQL.P Query SELECT ?person WHERE ?graph (?person km:skill km:Programming . ?person rdf:type km:Person ) (?graph swp:assertedBy ?warrant . ?warrant swp:authority ?author ) (?author km:affiliation ?project ) (?project rdf:type km:Project . ?project km:topic km:Programming ) AND COUNT(?project) >= 2 USING km FOR <http://www.example.org/vocabulary#> rdf FOR <http://www.w3.org/1999/02/22-rdf-syntax-ns#> swp FOR <http://www.w3.org/2004/03/trix/swp-1/> Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Query Result and Justification Tree ?person = http://www.example.org#Monica 16 Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Summary Highlighted the need for subjective, task-specific trust policies Proposed using context- and content-based trust mechanisms, beside of reputation-based mechanisms Proposed extending RDF to Named Graphs Proposed the Semantic Web Publishing Vocabulary Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Key References and Credits http://www.w3.org/2004/03/trix/ Named Graph Website Links to TriX, TriG, TriQL, RDFQ Specs http://www.hpl.hp.com/techreports/2004/HPL-2004-57.html Named Graphs, Provenance and Trust Carroll, Bizer, Pat Hayes and Patrick Stickler http://www.hpl.hp.com/techreports/2004/HPL-2004-56.html TriX: RDF Triples in XML update of initial named graphs paper by Carroll and Stickler http://www.wiwiss.fu-berlin.de/suhl/bizer/TriQLP More information about the TriQL.P trust architecture All papers, specs and sites are early versions, this is work-in- progress 17 Jeremy Carroll, Chris Bizer: The Semantic Web Trust Layer Thanks :-)
