Building Trustworthy Semantic Webs Lecture #7: OWL (Web Ontology Language) and Security Dr. Bhavani Thuraisingham September 2006

Objective of the Unit This unit will provide an overview of ontologies, OWL and then discuss some security issues

Outline of the Unit What are ontologies Why is RDF not sufficient? What are the security issues for ontologies What is OWL? OWL Syntax and Semantics Summary and Directions

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

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

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

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

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

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

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>

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>

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”/>

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>

Example Policies Temporal Access Control After 1/1/05, only doctors have access to medical records Role-based Access Control Manager has access to salary information Project leader has access to project budgets, but he does not have access to salary information What happens is the manager is also the project leader? Positive and Negative Authorizations John has write access to EMP John does not have read access to DEPT John does not have write access to Salary attribute in EMP How are conflicts resolved?

Privacy Policies Privacy constraints processing Simple Constraint: an attribute of a document is private Content-based constraint: If document contains information about X, then it is private Association-based Constraint: Two or more documents taken together is private; individually each document is public Release constraint: After X is released Y becomes private Augment a database system with a privacy controller for constraint processing

Access Control Strategy Subjects request access to OWL 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 Query Modification?

System Architecture for Access Control User Pull/Query Push/result RDF- Access RDF-Admin Admin Tools Credential base Policy base OWL Documents

OWL Databases Data is presented as OWL documents Query language? OWL=QL? Query optimization (depends on query language) Managing transactions on OWL documents Metadata management: OWL schemas? Access methods and index strategies OWL security and integrity management

Inference/Privacy Control Interface to the Semantic Web Technology By UTD Inference Engine/ Rules Processor (Reasoning in OWL?) Policies Ontologies Rules OWL Documents Web Pages, Databases OWL Data Management

Summary and Directions Ontologies are a necessity for the web OWL is getting recognition; several other ontology languages (DAML, OIL, etc.) Very little work on security and ontologies? How can we specify the policies in OWL? How can query modification be carried out for OWL documents? Design access control for OWL databases