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the semantic web a gide to the future of XML, Web Services and Knowledge Management - Daconta M,C.

Daconta M,C. the semantic web a gide to the future of XML, Web Services and Knowledge Management - Wiley publishing , 2003. - 304 p.
ISBN 0-471-43257-1
Download (direct link): thesemanticwebguideto2003.pdf
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E_1:
{{Person Instance: {John Q. Public},
Location Instances (constrained to US_Cities):
{US_Cities: Akron_Ohio},
Event Instances (constrained to Credit_Card_Purchases_of_Sporting_Events, Credit_Card_Purchases_of_Book_Merchandise, Credit_Card_Purchases_of_Clothing_Merchandise):
{Purchase1234_of_12-19-02, Purchase456789_of_12-19-02, Purchase556677_of_12-19-02}
{Person Instance: {Cynthia A. Citizen},
Location Instances (constrained to US_Cities):
{US_Cities: Peoria_Illinois},
Event Instances (constrained to Credit_Card_Purchases_of_Sporting_Events, Credit_Card_Purchases_of_Book_Merchandise, Credit_Card_Purchases_of_Clothing_Merchandise):
{Purchase890_of_12-19-02, Purchase13579_of_12-19-02, Purchase112233_of_12-19-02}}
In this example, John Q. Public in Akron, Ohio, and Cynthia A. Citizen in Peoria, Illinois, are the only individuals who had all three kinds of specific purchases (sporting events, books, clothing) using a credit card in any U.S. city on December 19, 2002.
Now, what if the My Theory of Interesting Things changes? What if tomorrow a marketing analyst has to add a new description of what constitutes Interesting Things? Let's assume that the new description just adds an additional
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Chapter 8
property, for instance, Intension I's Events Ev now also range over {Started_Flight_from_LaGuardia_Airport}.
The description I now changes to I' that is the same as I with the additional assertion that the Started_Flight_from_LaGuardia_Airport is also possible.
This means that if My Theory of Interesting Things changes (with the addition of a new property, for example), a new query could be generated that finds the extension of the new intension in the database. Correspondingly, the old extension could be evaluated with respect to the new intension and seen as to whether it holds or has a relation to the new extension of the new intension (that is, the new set for which the new description holds). Two intensions may have the same extensions; this is known as extensional equivalence. It can help you to know that the same individual has two different descriptions: Clark Kent and Superman. The man who saw Billie B's magic show at the Hyatt on 22nd St. yesterday and the man who charged an Aeroflot ticket with destination Rasputania at LaGuardia this morning could be the same person My Theory of Interesting Things could be modeled in the ontology (set of integrated ontologies) in the same way as any other domain ontology; it's a theory just as they are. A modeler can use the same mechanisms to model My Theory of Interesting Things as any other theory in the ontology—for instance, specialize it, inherit from it, modify it, and so on. A generic model of My Theory of Interesting Things could be created, which an individual analyst could specialize according to a set of new properties. Other marketing analysts could in turn specialize from that.
This means that the description changes. Things for which the old description held are updated. Things for which the new description holds are found. Links between the things described by the two descriptions are also found. You can model Things That Are of Interest to You (or My Theory of Interesting Things). In fact, you absolutely should. Your model can change, and it no doubt will.
Of course, the devil is in the details of the implementation. But if you are model-driven (meaning here ontology- or knowledge-driven), that just means you can change your model, regenerate the implementation, or find the delta, and continue.
Everything should be model-driven. It's much simpler to change the model (the description) than the thing that, without the model, has no well-defined semantics. Without a model, you are perpetually doomed to try to correlate tuples in multiple databases that have no accompanying semantics. This is why data mining and its parent, knowledge discovery, are such hot technologies now—this is the way we usually do things. No model, no semantics. So we try to infer the semantics, or what the data means. It's tough to do.
Understanding Ontologies
Levels of Representation
When discussing ontologies, you need to make distinctions among a number of representation levels. These distinctions are necessary because ontologies can be viewed as languages, or syntactic vocabularies with accompanying semantics. Furthermore, because ontologies are content and content can only be expressed using a content language, which is usually called a knowledge representation language (we discuss these in more detail in the next section), we are therefore talking about at least two levels of representation: the knowledge representation language level, typically called the meta level with respect to the underlying level, and the object level, which is the underlying content level, the level at which ontologies are expressed. But the notions of meta and object level are really relative to the particular levels one is talking about. We also know that we need a third level, the level of instances. This is the level at which instances of the ontology classes exist.
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