1. Lecture #13: RDF and RDF Security Dr. Bhavani Thuraisingham
Building Trustworthy
Semantic Webs
Lecture #13: RDF and RDF Security
Dr. Bhavani Thuraisingham
February 2010

2. Objective of the Unit
This unit will provide an overview of RDF and then discuss some security issues

3. Outline of the Unit Why RDF? What is RDF? RDF Specifications
RDF Schema (RFDS)
RDF Security
Policies in RDF
RDF Axiomatic Semantics and Inferencing
RDF Database
SPARQL
FOAF
Summary and Directions
Examples throughout the lecture

4. 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

5. 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

6. 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

7. RDF Specification <rdf: RDF
xmlns: rdf = “
xmlns: xsd = “
xmlns: uni = “
<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: RDF>

8. Example <?xml version="1.0"?> <rdf:RDF
The following example illustrates a part of an RDF document describing books: Building_Trustworthy_Semantic_Webs and Managing_and_Mining_Multimedia_Databases. They belong to Class ‘Book’ and have properties: author, publisher, year and ISBN.
<?xml version="1.0"?>
<rdf:RDF
xmlns:book="
xmlns:owl="
xmlns:rdf="
xmlns:rdfs="
<book:Book rdf:ID="Building_Trustworthy_Semantic_Webs">
<book:author>Bhavani Thuraisingham</book:author>
<book:publisher>Auerbach Publications</book:publisher>
<book:year>2007</book:year>

9. Example <book:ISBN>0849350808</book:ISBN>
</book:Book>
<book:Book rdf:ID="Managing_and_Mining_Multimedia_Databases">
<book:author>Bhavani Thuraisingham</book:author>
<book:publisher>CRC Press</book:publisher>
<book:year>2001</book:year>
<book:ISBN> </book:ISBN>
</rdf:RDF>

10. 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: subClassof rdf: resource = “academicStaffMember”/>
<rdfs: Class>

11. Example <The RDF schema for the above RDF document is as follows:
<?xml version="1.0"?>
<rdf:RDF
xmlns:owl="
xmlns:rdf="
xmlns:rdfs="
xmlns:wsp="
<rdfs:Class rdf:ID="Book">
<rdfs:comment>Book Class</rdfs:comment>
<rdfs:subClassOf rdf:resource=" ns#Resource"/>
</rdfs:Class>

12. Example <rdf:Property rdf:ID="author">
<rdfs:Comment>Author of the book</rdfs:Comment>
<rdfs:domain rdf:resource="#Book"/>
<rdfs:range rdf:resource="
</rdf:Property>
<rdf:Property rdf:ID="publisher">
<rdfs:Comment>Publisher of the book</rdfs:Comment>

13. Example <rdf:Property rdf:ID="year">
<rdfs:Comment>Year of first publication of the book</rdfs:Comment>
<rdfs:domain rdf:resource="#Book"/>
<rdfs:range rdf:resource="
</rdf:Property>
<rdf:Property rdf:ID="ISBN">
<rdfs:Comment>ISBN of the book</rdfs:Comment>
</rdf:RDF>

14. 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

15. RDF and Security
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?

16. RDF Policy Specification
<rdf: RDF
xmlns: rdf = “
xmlns: xsd = “
xmlns: uni = “
<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: RDF>

17. Policy Specification
The examples we have discussed earlier show how certain policies may be specified for RDF documents. A more detailed example is given below.
<?xml version="1.0"?>
<rdf:RDF
xmlns:book="
xmlns:owl="
xmlns:rdf="
xmlns:rdfs="
<book:Book rdf:ID="Building_Trustworthy_Semantic_Webs">
<book:author>Bhavani Thuraisingham</book:author>
Level = Secret
<book:publisher>Auerbach Publications</book:publisher>
Level = Confidential

18. Policy Specification <book:year>2007</book:year>
Level = Unclassified
<book:ISBN> </book:ISBN>
Level = Confidential
</book:Book>
<book:Book rdf:ID="Managing_and_Mining_Multimedia_Databases">
<book:author>Bhavani Thuraisingham</book:author>
Level = Secret
<book:publisher>CRC Press</book:publisher>

19. Policy Specification <book:year>2001</book:year>
Level = Unclassified
<book:ISBN> </book:ISBN>
</book:Book>
</rdf:RDF>

20. 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: subClassof rdf: resource = “academicStaffMember”/>
Level = L
<rdfs: Class>

21. 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)

22. 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

23. 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 = = ‘CS’]//Node()” priv = “VIEW”/>
Can reification be used to specify policies?

24. 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?

25. 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

26. Policies,in RDF
Now, in previous examples, we have specified policies for RDF documents. Now, can we use RDF to specify policies? That is, how can RDF be used to specify the following policy?
“Only those attending a class from a professor has read access to the lecture notes of the professor”
Below we specify this policy in RDF.
</rdf:RDF>
xmlns:uni=
xmlns:policy="
xmlns:rdf="
<uni:LectureNotes rdf:ID="Data_Quality.doc">
<uni:Author>Bhavani Thuraisingham</uni:author>
<policy:AccessBy rdf:resource=

27. Policies in RDF <rdf:RDF
xmlns:uni=
xmlns:policy="
xmlns:rdf=
<uni:Class rdf:ID="cs609">
<uni:taughtyBy>Bhavani Thuraisingham</book:author>
</rdf:RDF>

28. Access Control Strategy
Subjects request access to RDF 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?

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

30. RDF Databases Data is presented as RDF documents
Query language: RQL, SPARQL
Query optimization
Managing transactions on RDF documents
Metadata management: RDF Schemas?
Access methods and index strategies
RDF security and integrity management

31. 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”
SPARQL is the current query language for RDF

32. SPARQL
RDF is a directed, labeled graph data format for representing information in the Web.
SARQL specification defines the syntax and semantics of the SPARQL query language for RDF.
SPARQL can be used to express queries across diverse data sources, whether the data is stored natively as RDF or viewed as RDF via middleware.
SPARQL contains capabilities for querying required and optional graph patterns along with their conjunctions and disjunctions.
SPARQL also supports extensible value testing and constraining queries by source RDF graph.
The results of SPARQL queries can be results sets or RDF graphs.

33. RDF Databases select Book, NumInStock
from {Book} book:authoredBy {Author}
. book:Stock {NumInStock}
Where Author Like “Bhavani*”
using namespace
book =
The requestor does not have access to the number of book copies in the stock. Therefore, new modified Query:
select Book

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

35. Semantic Social Networks
The latest breed of social networking services combine social networks with the sharing of content such as bookmarks, documents, photos, reviews.
The use of of Semantic Web technology facilitated distributed control.
The friend-of-a-friend (FOAF) project is a first attempt at a formal, machine processable representation of user profiles and friendship networks. (Unlike with Friendster and similar sites that have central control)
FOAF profiles are created and controlled by the individual user and shared in a distributed fashion.

36. Sharif University of Technology, Semantic Web Course, Fall 2005
FOAF
The Friend of a Friend (FOAF) project is creating a Web of machine-readable pages describing people, the links between them and the things they create and do; it is a contribution to the linked information system known as the Web.
FOAF defines an open, decentralized technology for connecting social Web sites, and the people they describe.
FOAF is part of a shift towards a Web where we can choose the sites and tools we like, without being cut off from friends who made different choices.
FOAF lets you share and inter-connect information from diverse sources, move it around, and use it in unexpected new ways.
Sharif University of Technology,
Semantic Web Course, Fall 2005

37. FOAF Example
<foaf:Person rdf:about="#me“ xmlns:foaf="
<foaf:name>Dan Brickley</foaf:name>
<foaf:mbox_sha1sum>241021fb0e6289f92815fc210f9e c252e< /foaf:mbox_sha1sum>
<foaf:homepage rdf:resource=" /> <foaf:img rdf:resource="/images/me.jpg" />
</foaf:Person>

38. Summary and Directions
RDF is beginning to be used
Very little work on RDF security
How can we specify the policies discussed in this unit in RDF?
How can query modification be carried out for RDF documents?
Design access control for RDF databases