Sesame: An Architecture for Storing and Querying
RDF Data and Schema Information
Jeen Broekstra
Aidministrator Nederland b.v.
jeen.broekstra@aidministrator.nl
Arjohn Kampman
Aidministrator Nederland b.v.
arjohn.kampman@aidministrator.nl
Frank van Harmelen
Faculty of Sciences, Vrije Universiteit Amsterdam
frank.van.harmelen@cs.vu.nl
Abstract
RDF and RDF Schema provide the first W3C standard to enrich the Web with machine-processable
semantic data. However, to be able to use this semantic data, a scalable, persistent RDF store and a
powerful query engine using an expressive query language are needed.
Sesame is an extensible architecture implementing both of these. Sesame can be based on arbitrary
repositories, ranging from traditional Data Base Management Systems, to dedicated RDF triple stores.
Sesame also implements a query engine for RQL, the most powerful RDF/RDF Schema query lan-
guage to date.
1 Introduction
The Resource Description Framework (RDF) [Lassila and Swick, 1999] is a W3C Recommendation for
the notation of meta-data on the World Wide Web. RDF Schema [Brickley and Guha, 2000] extends this
standard by providing developers with the means to specify vocabulary and to model object structures.
These techniques will enable the enrichment of the Web with machine-processable semantics, thus giving
rise to what has been dubbed the Semantic Web.
However, simply having this data available is not enough. Tooling is needed to process the information,
to transform it, to reason with it. As a basis for this, we have developed Sesame, an architecture for efficient
storage and expressive querying of large quantities of RDF meta-data. Sesame is being developed by Aid-
ministrator Nederland b.v.1 as part of the European IST project On-To-Knowledge2 [Fensel et al., 2000].
This paper is organized as follows: in section 2 we give a short introduction to RDF and RDF Schema.
This section is only to make the paper self-contained, and can be skipped by readers already familiar
with these languages.
In section 3 we discuss why a query language specifically tailored to RDF and RDF Schema is needed,
over and above existing query languages such as XQuery. In section 4 and 5 we look in detail at
Sesame’s architecture. Section 6 discusses our experiences with Sesame until now, and section 7 looks into
possible future developments. Finally we provide our conclusions in section 8.
2 RDF and RDF Schema
The Resource Description Framework (RDF) [Lassila and Swick, 1999] is a W3C recommendation that
was originally designed to standardize the definition and use of metadata-descriptions of Web-based re-
sources. However, RDF is equally well suited to representing arbitrary data, be they meta-data or not.
1See http://www.aidministrator.nl/
2See http://wwww.ontoknowledge.org/
1

2.1 RDF
The basic building block in RDF is an object-attribute-value triple, commonly written as A(O; V ). That is,
an object O has an attribute A with value V . Another way to think of this relationship is as a labeled edge
between two nodes: [O]A! [V ].
This notation is useful because RDF allows objects and values to be interchanged. Thus, any object
from one triple can play the role of a value in another triple, which amounts to chaining two labeled edges
in a graphic representation. The graph in figure 1 for example, expresses the following relationships:
hasName
(’http://www.famouswriters.org/twain/mark’,
"Mark Twain")
hasWritten
(’http://www.famouswriters.org/twain/mark’,
’http://www.books.org/ISBN0001047582’)
title
(’http://www.books.org/ISBN0001047582’,
"The Adventures of Tom Sawyer")
http://www.famouswriters.org/twain/mark
"Mark Twain"
http://www.books.org/ISBN0001047582
"The Adventures of Tom Sawyer"
hasName
hasWritten
title
Figure 1: An example RDF data graph, capturing three statements
RDF also allows a form of reification3 in which any RDF statement itself can be the object or value
of a triple. This means graphs can be nested as well as chained. On the Web this allows us, for example,
to express doubt or support for statements created by other people. Finally, it is possible to indicate that a
given object is of a certain type, such as stating that “ISBN0001047582” is of the type Book, by creating a
type edge referring to the Book definition in an RDF schema:
type
(’http://www.books.org/ISBN0001047582’,
’http://www.description.org/schema#Book’)
The RDF Model and Syntax specification also proposes an XML syntax for RDF data models. One
possible serialisation of the above relations in this syntax, would look like this:
3rei facere (Lat.) ‘to make into a thing’
2