Evaluation Experiment for
Ontology Editors: SemTalk
The idea of
the evaluation experiment for ontology editors is to model a given text with
several semantic web related modelling
The sample
text to be modelled is a natural language description of a travelling domain
and the task is to model a given flight problem. This text is not a real world
document from a travel agency but a textual definition of a problem space. The
information given in that document can be regarded as instructions for
knowledge engineers how to model this specific domain. This has a major impact
on the resulting model:
- Concepts like ‘Car’, ‘Plane’
etc. usually have not to be explained to a user
- They need to be defined to do
machine based reasoning in this domain
- There are a couple of
ontologies out there which already describe this domain
The product
idea of SemTalk is to visualize complex scenarios, often described in
documents, with symbols understood by non-technical users. SemTalk is not a
On Finding Ontologies on
the Web for Referencing
In a
SemTalk typical scenario we would emphasise on the statements made in one
document and relate them to an external ontology. One of the most important
aspects of semantic web is to make sure that people are talking about the same
The first
step in order to create the demo model was a search on the internet for
existing ontologies.
Since there
is still no specific ontology search engine out there this has to be done using
Google and some background knowledge. Via http://www.daml.org/ontologies
searching for travel you will find:
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http://ontobroker.semanticweb.org/ontos/compontos/tourism_I1.daml |
A couple
of ontologies for travel posted by |
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The
interesting aspect about this one is, that the authors
have been modelling “B777” and “First Class” as instances. One other reason
not to use this ontology is that the current SemTalk did not understand daml:one-of and the missing
‘Restriction’ tag properly. |
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http://opencyc.sourceforge.net/daml/cyc-transportation.daml and |
The
problem with cyc-transportation ontology was, that the namespace for the objects did not match the
location of the file. |
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WordNet
may be used as an RDFS Webservice in order to lookup common words and return
their definition and taxonomy as RDFS. |
The result
of the experiment was, that we learned a lot about the syntactic variants of
how DAML / RDFS has been used in existing ontologies.
The
Design issues for the
SemTalk Model
SemTalk
offers an explorer / browser to navigate the inheritance structure of the
ontology. But the way SemTalk presents information to the end user is
graphically.
The structure
of the resulting SemTalk model in this experiment basically follows the
structure of the text. We have tried to capture the contents paragraph by
paragraph. For each paragraph a diagram (or “scenario”) has been built. The
thumb rule for the contents of a diagram is to make not more than 7
“statements” in one drawing. The diagrams actually contain now less than 20
objects each.
Ontologies
are basically are boring thing. This does not really matter as long as they are
used by machines, but it is an important issue if we are using them to transfer
knowledge between humans.
One way to
draw attention of people to models is to use pictures and symbols. SemTalk is
based on Visio with the intension to make use of the existing Visio shapes.
Visio shapes can be selected from a vector graphics based library shipped with
Visio, from Office Cliparts or just by using
arbitrary images. For this example we found it to be the fasted and most
convenient way to use images taken from Google’s
image search. Using a couple of images in the graphical drawing of the ontology
does not really add new information but it makes it more fun to read. Using an
existing image is done by copying the jpg to the hard
disk. Then drop it in the document stencil and rename it to the class name you
need.
Fig.1: The Vehicle Ontology
We have
attached the definition found in WordNet using a “Post-It”-style comment
object. This often helps to understand the ontology even if the contents of that definition is actually ignored by any
interpreter.
By
assigning a Visio Symbol to a class in the ontology a kind of domain specific
modelling
The
diagrams in detail are showing:
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A
taxonomy of vehicle classes mentioned in the text |
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Displaying
the fact stated in the text, that the agency is interested in subclasses of
planes. This diagram demonstrated how to use object properties in order to
express |
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This
diagram corresponds to the paragraph the text introducing attributes. The
appropriate style to do this in SemTalk is to use UML-style shapes to
visualize attributes. The focus of this diagram is to talk about the complex
relations between Trip, Flight, Transportation and |
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This
diagram does not add new constructs. It is basically there because it
implements a lot of text about the subclasses of hotels and gives us a chance
to add a picture of the |
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One of
the import aspects of the given text seemed to be the modelling of the
relation between vehicles, transportation types and locations. This diagram
shows how to do that in SemTalk again with property overloading. You may find
the information that a train journey starts and end at a railway station and
not at a seaport. For a train journey a train is used as a vehicle. |
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This is our
first instance diagram. It models the concrete destinations and continents as
instances. Since we have not assigned symbols for city and continent we have
used default shapes here. What we experienced as a missing feature in SemTalk
was the possibility to assign individual pictures to single instances. This
is currently only supported for classes. |
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SemTalk’s
native ontology modelling does not support a rule language or rule engine.
Solutions like Integral, a graphical rule editor for SAP’s Internet Pricing Configurator have been
built on top of SemTalk. |
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This
instance diagram shows simply the instances needed for |
The
resulting model can be published as HTML. In the HTML document we have added
source text with some hyperlinks to classes in the ontology.
We also can
export RDFS or DAML from
this SemTalk model. Classes only, instances only or both combined in one
file.
The DAML
files can be
- included as markup
in the original documents or
- stored as markup
besides the original documents or
- published on a server as a
reference ontologie or
- used as an ontology spell
checker within Office XP or
- ….