Transcript Joining the Semantic Web: a Practical Guide

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Joining the Semantic Web:
a Practical Guide.
Pasqualino “Titto” Assini
Nesstar Ltd - UK
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NESSTAR : The “Data Web”
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• The Data Web is the application of
Semantic Web techniques and
principles to the problem of statistical
data and metadata (surveys, opinions
polls) dissemination and processing.
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Joining the Semantic Web in A Few Easy(?)
Steps
• Know What You Want To Say  Modelling
• Then Say It -> Map the Model to a Semantic Web
Language
• Think of the Future  Managing Change
• Let Everybody Know  Publishing on the Semantic
Web
• Make Your Entities Behave  Specifying
Operations/Services
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Additional Considerations
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• Keep it Simple Or Else  Why Being Too
Clever Doesn’t Work on the Internet.
• XML – Friend or Foe of the Semantic Web?
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Know What You Want To Say
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• The Semantic Web is no silver bullet. It won’t
help you in modelling your data.
• Use your existing modelling language (and
models).
• You can also use RDF/RDF Schema but:
– Not many (graphical tools) tools
– Not much expressive power (example: no
relationships)
• Tip: Use standard UML design tools (in most
cases a UML Class Diagram is all you need)
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Now Say It
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• Once you have you model you need to
translate it to a Semantic Web Language:
– Choose the target language: RDF, WOL
– Define the mapping rules (might be already
defined, UML  RDF)
• What about using a specialised XML syntax?
– Advantage: More compact/simpler syntax
– Disadvantage: Difficult to design properly, need to
define an additional mapping to RDF.
• Tip: Stick to standard RDF syntax.
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Managing Change
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• Fact of Life: things change, models do as
well.
• Specific Application/Clients will need to
extend your core model.
• Good News: RDF was custom made to be
extensible (class/property inheritance,
additional properties, reification)
• Tip: Make sure that your applications can
handle model extensions.
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Publishing on the Semantic Web
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• Wrong assumption: You need something
special, a Registry maybe (e.g, UDDI)
• This can be real easy, just do it the WWW
way.
• Self-description principle: objects and types
self-describe themselves by making
accessible, via HTTP, their RDF description at
their URL.
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Specifying Behaviour
• Example: Bank Account operations to pay in or
draw money.
• The Semantic Web is silent on this point.
• Major oversight  Web Services come to the
rescue.
• Problem: Web Services and the Semantic Web
are not well integrated (but we might soon have an
RDF model of WSDL).
• Can’t wait? Use what is available: DAML-S,
NEOOM (simple RDF model of methods plus
method invocation via HTML FORMs).
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Keep It Simple or Else
• Fact: The value of an information
dissemination system depends on the
quantity of information it contains and the
number of eyeballs looking at it.
• Therefore: initially the system is worthless
(the Web was, the Semantic Web still is).
• But, if it starts growing it can grow real fast.
• So: how do you get the snowball going? KISS
to lure early adopters.
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XML - Friend of Foe ?
• (RDF/)XML is very hard to write by hand and not
particularly pleasant to read.
• It would be very useful if people (early adopters) could
jot down semantic web descriptions without tools
(think of HTML).
• TBL has lately engaged in an unofficial and very
politically incorrect activity: defining a non-XML syntax
for RDF: N3.
• What about an official W3C initiative to create a
semantic web language that is not only machine
understandable but also easy for an human to read
and write?
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