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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] RE: Re: semantics in schema (xsd)
 As has been pointed out: 1. The problem is not with the ontology technology. The problem is with rules applied to membership that are then assumed to have a meaningful relationship to real world entities, particularly in the the co-occurrence constraints (business rules). 2. That the scope of application and the abstract domain are not necessarily the same. 3. That the best approach to implementing these can be to create an extensible enumeration of the relationship types given that the domain of application may vary significantly by locale, that is, the ontology itself may have to be very weak to have a global scope. Regardless of the purity of the abstractions of the ontological instance or its metalanguage, the social dimensions of the application domain are a powerful selector of the technology applied, where the rules and relationships are declared and what they are locale by locale. In the example provided, the problem of a single viewpoint is clear: at the Constitutional level, at the Federal level, at the state level, at the agency level, at the individual level, the ontological distinctions and the co-occurrence values are distinctly different. len From: Pete Kirkham [mailto:pete.kirkham@b...] (a little late as I've been away for a long weekend) Irene Polikoff: > Well, this seem to go back to the question of whether "husband" should > be treated as a class - a subclass of males or as a relationship (object > property). In the ontology, the class describes a set of things with common properties, this should not be confused with a type in an information model/schema or a class in an OO implementation that encapsulates the data that represents the information that is a viewpoint on the abstract concept that is described by the ontological classification. So the ontology may have husband as a class- as there is a 'meaningful' set of human individuals that share the properties maleness and marriage, and an information model for on application of that ontology may only have the capability of representing husbands with female spouses. All information models of real world situations appear doomed to incompleteness. David Megginson: > I'd say forget about classes and make your objects big bags of properties > (attributes and relationships). The main advantages of classes for > object-oriented programming -- code reuse and type-safe polymorphism -- > don't even apply to simple information representation, so why pay the costs > of a class structure if you don't receive any benefits? The benefit of classifying concepts gives a shorthand to help us reason about things- it's easier to agree what a husband is, then talk about what information the application needs to represent about or process when dealing with husbands than it is to always talk about 'individuals who are in a legally married state who are also male and human'. > There exists an entity A. > A is human. > A is male. To me, at the ontological level, these are classes, irrespective of whether or how you choose to implement the data level in static typed OO software. Given all statements may have a temporal limit, there's no problem with one web page from 1997 saying 'Fred is a husband' and another from 1993 saying 'Fred is not a husband'; OWL specifically notes that data in web documents may change and be inconsistent. If not, then nothing would be able to be classified, as nothing real is permanent. In OWL, even if you define only the relations, I can define a class based solely on the presence of those relations, and declare that your statements indicate a classification. AFAICT this is the main interoperation mechanism that OWL uses- saying that from your information model {x: x is a Human & x is a Male & x is married to y} is equivalent to my {x: x marital status = husband } class, if my information model only represents marital status as an enumeration. Such mappings apply only for the information mapped, so tomorrow an individual may be in a different classification. It's always possible to construct classes from relationships in the ontology, and this seems to be done best by what is meaningful in the domain. In the information model, the types will be based on what is useful to the applications that are using the information. It may be useful to limit husbands to current heterosexual relationships for one application, for another (e.g. a pension scheme), the instances considered as members of the husband type may include deceased partners. The software constructs that encapsulate the data may end up being very different to the ontological classifications and the information model types, simply because the software has to be written a certain way to work. Hence, in a static OO language, you end up with David's implementation, irrespective of the concepts embodied. But capturing the classifications that make up the ontology shouldn't be constrained by the limits of one programming paradigm that may be used to implement one application in that domain. Pete ******************************************************************** This email and any attachments are confidential to the intended recipient and may also be privileged. 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