Graffoo, a Graphical Framework for OWL Ontologies

Graffoo, a Graphical Framework for OWL Ontologies [1], is a wonderful new open source tool developed by Silvio Peroni that can be used to present the classes, properties and restrictions within OWL ontologies, or sub-sections of them, as clear and easy-to-understand diagrams. Several Graffoo diagrams have been developed to explain SPAR ontologies, or portions of them, and are to be found in the appropriate ontology directories at

For example, in Figure 1 the diagram, BiRO.png, illustrates the structure of BiRO, the Bibliographic Reference Ontology:

Graffoo diagram of BiRO, the Bibliographic Reference Ontology

The upper part of this diagram shows how a bibliographic record, which in FRBR terminology is a Work, (a) is a set of components (author names, publication year, title, volume number, ISSN, publisher, dates of submission, acceptance and publication, etc.), (b) references a published entity (a FRBR Endeavor), and (c) can form part of a bibliographic collection such as a library catalogue, which is also a set of components, in this case of bibliographic records.

The lower part of the diagram shows how such a bibliographic record can be realized (i.e. expressed in a specific form, forming what in FRBR terminology is an Expression) as a bibliographic reference, such as you might find in an article’s reference list. The bibliographic reference, while referencing the same published entity, differs from a bibliographic record in two important ways.

  • First, a bibliographic reference typically does not include all the components of the full bibliographic record. References typically exclude the ISSN, the name of the publisher, and the submission and acceptance dates; may exclude the publication date and some of the authors’ names if there are many authors; and in certain journal (e.g. Nature) also exclude the title.
  • Second, the components of a bibliographic reference form an ordered list rather than a set, although the precise order of components can vary from journal to journal (e.g. whether or not the publication year immediately follows the authors’ names).

The diagram also shows that, just as bibliographic records may be grouped into bibliographic collections, so bibliographic references may be grouped into bibliographic lists such as reference lists (which, of course, are themselves ordered lists), nicely exposing the symmetry within the BiRO ontology in a manner that would be hard to grasp simply by looking at the class structure within an ontology editor such as Protégé.

The advantages of using such a Grafoo diagram are thus that it displays the logical relationships between elements of an ontology, or a sub-section of an ontology, in a manner that is relatively straightforward to understand, once one has grasped the meaning of the different elements of a Graffoo diagram. These elements are shown and defined in the Graffoo key (Figure 2).

Figure 2: The legend for all possible Graffoo objects

From our preliminary empirical studies, it appears that Graffoo allows us to create representations of OWL ontologies that can be comprehended in detail without the person viewing them having to understand the details of OWL 2 or of any of its linearizations (Turtle, RDF/XML, Manchester Syntax, or OWL/XML).

Graffoo has been developed using the standard library of the yEd diagram editor, a free diagram editor running on Windows, Mac and Linux. The graphml format version of those Graffoo objects is also available here. We commend the use of Graffoo to other ontologists.

[1] Graffoo, the Graphic framework for OWL ontologies.

Using LODE for ontology visualization

Silvio Peroni has recently created LODE (Live OWL Documentation Environment;, a new ontology visualization service that automatically extracts classes, object properties, data properties, named individuals, annotation properties, general axioms and namespace declarations from an OWL or OWL2 ontology, and renders them as ordered lists, together with their textual definitions, in a human-readable HTML page designed for browsing and navigation by means of embedded links.  The Cascading Style Sheets used for this page are based on the W3C CSSs for Recommendation documents.

This LODE service is an open source development, and can be freely used, as described at It may be used in conjunction with content negotiation to display the human-readable LODE version of an OWL ontology when the user accesses the ontology using a web browser, or alternatively to deliver the OWL ontology itself when the user accesses the ontology using an ontology editing tool such as Protégé and NeOn Toolkit.  It is in this way that LODE is being employed to visualize the SPAR (Semantic Publishing and Referencing) Ontologies (

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