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Dr. Bhavani Thuraisingham The University of Texas at Dallas Lecture #9 Trustworthy Semantic Webs

Data and Applications Security Developments and Directions. Dr. Bhavani Thuraisingham The University of Texas at Dallas Lecture #9 Trustworthy Semantic Webs February 2010. Outline. Semantic web XML and XML security RDF and RDF security Ontologies Rules Applications Reference:

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Dr. Bhavani Thuraisingham The University of Texas at Dallas Lecture #9 Trustworthy Semantic Webs

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  1. Data and Applications Security Developments and Directions Dr. Bhavani Thuraisingham The University of Texas at Dallas Lecture #9 Trustworthy Semantic Webs February 2010

  2. Outline • Semantic web • XML and XML security • RDF and RDF security • Ontologies • Rules • Applications • Reference: • Building trustworthy semantic web, Thuraisingham, CRC Press, 2007

  3. From Today’s Web to Semantic web • Today’s web • High recall, low precision: Too many web pages resulting in searches, many not relevant • Sometimes low recall • Results sensitive to vocabulary: Different words even if they mean the same thing do not results in same web pages • Results are single web pages not linked web pages • Semantic web • Machine understandable web pages • Activities on the web such as searching with little or no human intervention • Technologies for knowledge management, e-commerce, interoperability • Solutions to the problems faced by today’s web

  4. Knowledge Management and Personal Agents • Knowledge Management • Corporation Need: Searching, extracting and maintaining information, uncovering hidden dependencies, viewing information • Semantic web for knowledge management: Organizing knowledge, automated tools for maintaining knowledge, question answering, querying multiple documents, controlling access to documents • Personal Agent • John is a president of a company. He needs to have a surgery for a serious but not a critical illness. With current web he has to check each web page for relevant information, make decisions depending on the information provided • With the semantic web, the agent will retrieve all the relevant information, synthesize the information, ask John if needed, and then present the various options and makes recommendations

  5. E-Commerce • Business to Consumer • Users shopping on the web; wrapper technology is used to extract information about user preferences etc. and display the products to the user • Use of semantic web: Develop software agents that can interpret privacy requirements, pricing and product information and display timely and correct information to the use; also provides information about the reputation of shops • Business to Business • Organizations work together and carrying out transactions such as collaborating on a product, supply chains etc. With today’s web lack of standards for data exchange • Use of semantic web: XML is a big improvement, but need to agree on vocabulary. Future will be the use of ontologies to agree on meanings and interpretations

  6. Semantic Web Technologies • Explicit metadata: • Metadata is data about data; Need metadata to be explicitly specified so that different groups and organizations will know what is on the web • Metadata specification languages include XML and RDF • Ontologies • Explicit and formal specification of conceptualization describes a domain of discourse; relationships • Ontology languages include XML, RDF, OWL • Logic • Logic can be used to specify facts as well as rules; New facts and derived from existing facts based on the inference rules • Descriptive Logic is the type of logic that has been developed for semantic web applications

  7. Layered Approach: Tim Berners Lee’s Visionwww.w3c.org

  8. What is XML all about? • XML is needed due to the limitations of HTML and complexities of SGML • It is an extensible markup language specified by the W3C (World Wide Web Consortium) • Designed to make the interchange of structured documents over the Internet easier • Key to XML used to be Document Type Definitions (DTDs) • Defines the role of each element of text in a formal model • XML schemas have now become critical to specify the structure • XML schemas are also XML documents

  9. XML Elements XML Statement John Smith is a Professor in Texas This can be expressed as follows: <Professor> <name> John Smith </name> <state> Texas </state> </Professor>

  10. XML Elements Now suppose this data can be read by anyone then we can augment the XML statement by an additional element called access as follows. <Professor> <name> John Smith </name> <state> Texas </state> <access> All, Read </access> </Professor>

  11. XML Elements If only HR can update this XML statement, then we have the following: <Professor> <name> John Smith </name> <state> Texas </state> <access> HR department, Write </access> </Professor>

  12. XML Elements We may not wish for everyone to know that John Smith is a professor, but we can give out the information that this professor is in Texas. This can be expressed as: <Professor> <name> John Smith, Govt-official, Read </name> <state> Texas, All, Read </state> <access> HR department, Write </access> </Professor>

  13. XML Attributes Suppose we want to specify to access based on attribute values. One way to specify such access is given below. <Professor Name = “John Smith”, Access = All, Read Salary = “60K”, Access = Administrator, Read, Write Department = “Security” Access = All, Read </Professor Here we assume that everyone can read the name John Smith and Department Security. But only the administrator can read and write the salary attribute.

  14. XML DTD DTDs essentially specify the structure of XML documents. Consider the following DTD for Professor with elements Name and State. This will be specified as: <!ELEMENT Professor Officer (Name, State)> <!ELEMENT name (#PCDATA)> <!ELEMENR state (#PCDATA)> <!ELEMENT access (#PCDATA).>

  15. XML Schema While DTDs were the early attempts to specify structure for XML documents, XML schemas are far more elegant to specify structures. Unlike DTDs XML schemas essentially use the XML syntax for specification. Consider the following example: <ComplexType = name = “ProfessorType”> <Sequence> <element name = “name” type = “string”/> <element name = “state” type = “string”/> <element name = “access” type = “strong/> <Sequence> </ComplexType>

  16. XML Namespaces Namespaces are used for DISAMBIGUATION <CountryX: Academic-Institution Xmlns: CountryX = http://www.CountryX.edu/Instution DTD” Xmlns: USA = “http://www.USA.edu/Instution DTD” Xmlns: UK = “http://www.UK.edu/Instution DTD” <USA: Title = College USA: Name = “University of Texas at Dallas” USA: State = Texas” <UK: Title = University UK: Name = “Cambridge University” UK: State = Cambs </CountryX: Acedmic-Instiution>

  17. XML Namespaces <Country: Academic-Institution <Access = Government-official, Read </Access> Xmlns: CountryX = http://www.CountryX.edu/Instution DTD” Xmlns: USA = “http://www.USA.edu/Instution DTD” Xmlns: UK = “http://www.UK.edu/Instution DTD” <USA: Title = College USA: Name = “University of Texas at Dallas” USA: State = Texas” <UK: Title = University UK: Name = “Cambridge University” UK: State = Cambs </CountryX: Academic-Institution>

  18. Federations/Distribution Site 1 document: <Professor-name> <ID> 111 </ID> <Name> John Smith </name> <State> Texas </state> </Professor-name> Site 2 document: <Professor-salary> <ID> 111 </ID> <salary> 60K </salary> <Professor-salary>

  19. Credentials in XML <Professor credID=“9” subID = “16: CIssuer = “2”> <name> Alice Brown </name> <university> University of X <university/> <department> CS </department> <research-group> Security </research-group> </Professor> <Secretary credID=“12” subID = “4: CIssuer = “2”> <name> John James </name> <university> University of X <university/> <department> CS </department> <level> Senior </level> </Secretary>

  20. Policies in XML <? Xml VERSION = “1.0” ENCODING = “utf-8”?> <Policy–base> <policy-spec cred-expr = “//Professor[department = ‘CS’]” target = “annual_ report.xml” path = “//Patent[@Dept = ‘CS’]//Node()” priv = “VIEW”/> <policy-spec cred-expr = “//Professor[department = ‘CS’]” target = “annual_ report.xml” path = “//Patent[@Dept = ‘EE’] /Short-descr/Node() and //Patent [@Dept = ‘EE’]/authors” priv = “VIEW”/> <policy-spec cred-expr = - - - - <policy-spec cred-expr = - - -- </Policy-base> Explantaion: CS professors are entitled to access all the patents of their department. They are entitled to see only the short descriptions and authors of patents of the EE department

  21. Access Control Strategy • Subjects request access to XML documents under two modes: Browsing and authoring • With browsing access subject can read/navigate documents • Authoring access is needed to modify, delete, append documents • Access control module checks the policy based and applies policy specs • Views of the document are created based on credentials and policy specs • In case of conflict, least access privilege rule is enforced • Works for Push/Pull modes

  22. System Architecture for Access Control User Pull/Query Push/result X-Access X-Admin Admin Tools Credential base Policy base XML Documents

  23. Third-Party Architecture • The Owner is the producer of informationIt specifies access control policies • The Publisher is responsible for managing (a portion of) the Owner information and answering subject queries • Goal: Untrusted Publisher with respect to Authenticity and Completeness checking XML Source policy base Credential base SE-XML Owner Publisher Reply document credentials Query User/Subject

  24. XML Databases • Data is presented as XML documents • Query language: XML-QL • Query optimization • Managing transactions on XML documents • Metadata management: XML schemas/DTDs • Access methods and index strategies • XML security and integrity management

  25. Inference/Privacy Control Interface to the Semantic Web Technology By UTD Inference Engine/ Rules Processor Policies Ontologies Rules XML Documents Web Pages, Databases XML Database

  26. Why RDF? • XML cannot be used to specify semantics • Example: • Professor is a subclass of Academic Staff • Professor inherits all properties of Academic Staff • RDF was specified so that the inadequacies of XML could be handled • RDF uses XML Syntax • Additional constructs are needed for RDF

  27. RDF • Resource Description Framework is the essence of the semantic web • Adds semantics with the use of ontologies, XML syntax • RDF Concepts • Basic Model • Resources, Properties and Statements • Container Model • Bag, Sequence and Alternative

  28. RDF Basics • Resource: Everything is a resource • Person, Vehicle, etc. • Property: properties describe relationships between resources • E.g., Invented • Statement: (Object, Property, Value) Triple • Berners Lee invented the Semantic Web

  29. RDF Container Model • Bag: Unordered container, may contain multiple occurrences • Rdf: Bag • Seq: Ordered container, may contain multiple occurrences • Rdf: Seq • Alt: a set of alternatives • Rdf: Alt

  30. RDF Specification <rdf: RDF xmlns: rdf = “http://w3c.org/1999/02-22-rdf-syntax-ns#” xmlns: xsd = “http:// - - - xmlns: uni = “http:// - - - - <rdf: Description: rdf: about = “949352” <uni: name = Berners Lee</uni:name> <uni: title> Professor < uni:title> </rdf: Description> <rdf: Description rdf: about: “ZZZ” < uni: bookname> semantic web <uni:bookname> < uni: authoredby: Berners Lee <uni:authoredby> </rdf: Description> </rdf: RDF>

  31. RDF Specification • RDF specifications have been given for Attributes, Types Nesting, Containers, etc. • How can security policies be included in the specification • Example: consider the statement “Berners Les is the Author of the book Semantic Web” • Do we allow access to the connection between author and book? Do we allow access to the connection but not to the author name and book name?

  32. RDF Policy Specification <rdf: RDF xmlns: rdf = “http://w3c.org/1999/02-22-rdf-syntax-ns#” xmlns: xsd = “http:// - - - xmlns: uni = “http:// - - - - <rdf: Description: rdf: about = “949352” <uni: name = Berners Lee</uni:name> <uni: title> Professor < uni:title> Level = L1 </rdf: Description> <rdf: Description rdf: about: “ZZZ” < uni: bookname> semantic web <uni:bookname> < uni: authoredby: Berners Lee <uni:authoredby> Level = L2 </rdf: Description> </rdf: RDF>

  33. RDF Schema • Need RDF Schema to specify statements such as professor is a subclass of academic staff <rdfs: Class rdf: ID = “professor” <rdfs: comment> The class of Professors All professors are Academic Staff Members. <rdfs: comment> <rdfs: subClassof rdf: resource = “academicStaffMember”/> <rdfs: Class>

  34. RDF Schema: Security Policies • How can security policies be specified? <rdfs: Class rdf: ID = “professor” <rdfs: comment> The class of Professors All professors are Academic Staff Members. <rdfs: comment> <rdfs: subClassof rdf: resource = “academicStaffMember”/> Level = L <rdfs: Class>

  35. RDF Axiomatic Semantics • First order logic to specify formulas and inferencing • Built in functions (First) and predicates (Type) • Modus Ponens • From A and If A then B, deduce B • Example: All containers are Resources • Type(?C, Container)  Type(?c, Resource) • If we have Type(A, Container) then we can infer (Type A, Resource)

  36. RDF Inferencing • While first order logic provides a proof system, it will be computationally infeasible • As a result horn clause logic was developed for logic programming; this is still computationally expensive • RDF uses If then Rules • IF E contains the triples (?u, rdfs: subClassof, ?v) and (?v, rdfs: subClassof ?w) THEN E also contains the triple (?u, rdfs: subClassOf, ?w) That is, if u is a subclass of v, and v is a subclass of w, then u is a subclass of w

  37. RDF Query • One can query RDF using XML, but this will be very difficult as RDF is much richer than XML • Is there an analogy between say XQuery and a query language for RDF? • RQL – an SQL-like language has been developed for RDF • Select from “RDF document” where some “condition”

  38. Policies in RDF • How can policies be specified? • Should policies be specified as shown in the examples, extensions to RDF syntax? • Should policies be specified as RDF documents? • Is there an analogy to XPath expressions for RDF policies? • <policy-spec cred-expr = “//Professor[department = ‘CS’]” target = “annual_ report.xml” path = “//Patent[@Dept = ‘CS’]//Node()” priv = “VIEW”/>

  39. Ontology • Common definitions for any entity, person or thing • Several ontologies have been defined and available for use • Defining common ontology for an entity is a challenge • Mappings have to be developed for multiple ontologies • Specific languages have been developed for ontologies

  40. Why RDF is not sufficient? • RDF was developed as XML is not sufficient to specify semantics • E.g., class/subclass relationship • RDF has issues also • Cannot express several other properties such as Union, Interaction, relationships, etc • Need a richer language • Ontology languages were developed by the semantic web community for this purpose • Essentially RDF is not sufficient to specify ontologies

  41. Security and Ontology • Ontologies used to specify security policies • Example: OWL to specify security policies • Choice between XML, RDF, OWL, Rules ML, etc. • Security for Ontologies • Access control on Ontologies • Give access to certain parts of the Ontology

  42. OWL: Background • It’s a language for ontologies and relies on RDF • DARPA (Defense Advanced Research Projects Agency) developed early language DAML (DARPA Agent Markup Language) • Europeans developed OIL (Ontology Interface Language) • DAML+OIL combines both and was the starting point for OWL • OWL was developed by W3C

  43. OWL Features • Subclass relationship • Class membership • Equivalence of classes • Classification • Consistency (e.g., x is an instance of A, A is a subclass of B, x is not an instance of B) • Three types of OWL: OWL-Full, OWL-DL, OWL-Lite • Automated tools for managing ontologies • Ontology engineering

  44. OWL Specification (e.g., Classes) < owl: Class rdf: about = “#associateProfessor”> <owl: disjointWith rdf: resource “#professor”/> <owl: disjointWith rdf: resource = #assistantProfessor”/> </owl:Class> <owl: Class rdf: ID = “faculty”> <owl: equivalentClass rdf: resource = “academicStaffMember”/> </owl: Class> Faculty and Academic Staff Member are the same Associate Professor is not a professor Associate professor is not an Assistant professor

  45. OWL Specification (e.g., Property) Courses are taught by Academic staff members < owl: ObjectProperty rdf: about = “#isTaughtby”> <rdfs domain rdf: resource = “#course”/> <rdfs: range rdf: resource = “#academicStaffMember”/> <rdfs: subPropertyOf rdf: resource = #involves”/> </owl: ObjectProperty>

  46. OWL Specification (e.g., Property Restriction) All first year courses are taught only by professors < owl: Class rdf: about = “#”firstyearCourse”> <rdfs: subClassOf> <owl: Restriction> <owl: onProperty rdf: resource = “#isTaughtBy”> <owl: allValuesFrom rdf: resource = #Professor”/> </rdfs: subClassOf> </owl: Class>

  47. Policies in OWL • How can policies be specified? • Should policies be specified as shown in the examples, extensions to OWL syntax? • Should policies be specified as OWL documents? • Is there an analogy to XPath expressions for OWL policies? • <policy-spec cred-expr = “//Professor[department = ‘CS’]” target = “annual_ report.xml” path = “//Patent[@Dept = ‘CS’]//Node()” priv = “VIEW”/>

  48. Policies in OWL: Example < owl: Class rdf: about = “#associateProfessor”> <owl: disjointWith rdf: resource “#professor”/> <owl: disjointWith rdf: resource = #assistantProfessor”/> Level = L1 </owl:Class> <owl: Class rdf: ID = “faculty”> <owl: equivalentClass rdf: resource = “academicStaffMember”/> Level = L2 </owl: Class>

  49. Logic and Inference • First order predicate logic • High level language to express knowledge • Well understood semantics • Logical consequence - inference • Proof systems exist • Sound and complete • OWL is based on a subset of logic – descriptive logic

  50. Why Rules? • RDF is built on XML and OWL is built on RDF • We can express subclass relationships in RDF; additional relationships can be expressed in OWL • However reasoning power is still limited in OWL • Therefore the need for rules and subsequently a markup language for rules so that machines can understand

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