Databases Reference
In-Depth Information
W3C (World Wide Web Consortium) is specifying standards for XML
security. The XML security project (see [20]) is focusing on providing the im-
plementation of security standards for XML. The focus is on XML-Signature
Syntax and Processing, XML-Encryption Syntax and Processing, and XML
Key Management. W3C also has a number of working groups including XML
Signature working group (see [21]) and XML encryption working group (see
[22]). While the standards are focusing on what can be implemented in the
near-term, much research is needed on securing XML documents.
3.5 RDF Security
RDF is the foundations of the semantic web. While XML is limited in pro-
viding machine understandable documents, RDF handles this limitation. As
a result, RDF provides better support for interoperability as well as searching
and cataloging. It also describes contents of documents as well as relation-
ships between various entities in the document. While XML provides syntax
and notations, RDF supplements this by providing semantic information in a
standardized way.
The basic RDF model has three types: they are resources, properties and
statements. Resource is anything described by RDF expressions. It could be
a web page or a collection of pages. Property is a specific attribute used to
describe a resource. RDF statements are resources together with a named
property plus the value of the property. Statement components are subject,
predicate and object. So for example, if we have a sentence of the form “John is
the creator of xxx”, then xxx is the subject or resource, property or predicate
is “Creator” and object or literal is “John”. There are RDF diagrams very
much like say ER diagrams or object diagrams to represent statements. It is
important that the intended interpretation be used for RDF sentences. This
is accomplished by RDF schemas. A schema is sort of a dictionary and has
interpretations of various terms used in sentences.
More advanced concepts in RDF include the container model and state-
ments about statements. The container model has three types of container
objects, and they are Bag, Sequence, and Alternative. A bag is an unordered
list of resources or literals. It is used to mean that a property has multiple
values but the order is not important. A sequence is a list of ordered resources.
Here the order is important. Alternative is a list of resources that represent
alternatives for the value of a property. Various tutorials in RDF describe the
syntax of containers in more detail.
RDF also provides support for making statements about other statements.
For example, with this facility one can make statements of the form “The
statement A is false” where A is the statement “John is the creator of X”.
Again one can use object-like diagrams to represent containers and statements
about statements. RDF also has a formal model associated with it. This formal
model has a formal grammar. For further information on RDF, we refer to
the excellent discussion in the topic by Antoniou and van Harmelen [13].
