- From: Gary Ng <Gary.Ng@cerebra.com>
- Date: Mon, 16 Jan 2006 03:25:55 -0800
- To: "SWBPD list" <public-swbp-wg@w3.org>
Elisa, Sorry for the delay in sending these out. I took some extra time to read it more carefully. I have mainly focused on the OWL Chapter of [1], with some look ups into the DL and RDF Metamodel chapters. The original reference to the doc is at [2]. The OWL descriptions are accurate. I believe it has covered all OWL constructs with minor quibbles. See "Quibbles" below with minor change suggestions. Recap: Base on the OWL abstract syntax, the metamodel covers all language elements of OWL (OWLBase). The base model is a minimally constraining specification. The sub-language variants are achieved per application/vendor by constraining the usage of the elements, provided as additional contraint packages. The OWLDL and OWLFull Constraints Package have yet to be defined and I understand Peter Patel-S and Bijan are helping to define those. Comment: Generally I find the interaction between RDF Document, OWL Graph, RDF and OWL statements, together with OWL Universe, needs some clarification. My concern can be summarized in the following questions, I find that the answers are probably implied within the text, but I haven't found satisfactory answers by myself and I need some help: 1. It seems OWL Universe, OWL Statements and OWL Graph are meant to be derived objects that tool vendors are to support? No end-users will need to explicitly specify them? 2. In 12.2.2: "As shown in Figure 14, an OWL ontology consists of a collection of facts, axioms, and annotations, defined in terms of zero or more RDF graphs and statements." Can statements made in RDF that represent OWL Expressions readily translatable into OWLBase constructs? Can a resource graph specified in the RDF profile be readily usable as an OWL instance graph? From the other direction, RDFGraph contains RDF Statements. OWLGraph is a subset of RDFGraph. Not all graphs are valid OWL Graph. But does this mean that all OWL Expressions are also RDF Statements, just like the relationship between RDF and OWL syntax? Need to clarify that whether axioms and expressions made using OWL Metamodel has an equivalent RDF Statement form just like the language. But if the OWL Metamodel is based on the abstract syntax, which means it does not necessary correspond to the RDF syntax for axioms, which in turn would mean the OWL Ontology contains RDF Graphs + some objects which can only be accessed through OWL Universe? 3. There seems to be two ways to specify an RDF triple? One is to use a Statement stereotype, the other is to literally associate one object to another with a link. The former allows reification, and associate the statement with a graph, the latter doesn't, and the fact that it becomes a statement is actually implicit. Or is it the case that all triples must be specified through a statement object with 3 links to subject, predicate, object explicitly, such that reification and or named graphs can be specified? 4. Not really about the OWL MetaModel, but will we expect a rewrite of the DL MetaModel (Appendix C)? What is expected to be done with it? It looks like it still needs a lot of work. ============================ Quibbles ============================ Naming consistency: Suggest the names RDFGraph (for RDF) and OWLStatement (for OWL) rather than Graph (for RDF) and Statement (for OWL). Thus it is clear that there are: RDFGraph, RDFStatement, OWLGraph, OWLStatement. 12.3.6 Individuals SameIndividual and DifferentIndividual with associations sameIndividual and differentIndividual have not been introduced before or anywhere else in this chapter. 12.3.11 OWLDataRange OWL DataRange can also be the rdfs:range of a Property but is missing here. It is certainly not in the RDF Metamodel and thus should be included here. 12.3.13 RDFProperty rdfs:domain and rdfs:range of property is covered in the RDFMetamodel and is not covered here. In the spirit of completeness, perhaps a pointer here to section 11.5.1 where they are described would be good. Since they are also an integral part of OWL. 12.4 OWLBase Property Under the meta class Property, the siblings specified here are: FunctionalProperty, DatatypeProperty, ObjectProperty; Under ObjectProperty, there are InverseFunctional, SymmetricProperty, and TransitiveProperty. I thought in OWL-Full DatatypeProperty may be InverseFunctional? The organization certainly suggests that if it is inverse functional, it is automatically object property, which is the case in DL. I went to checked the webont reference: "NOTE: Because in OWL Full datatype properties are a subclass of object properties, an inverse-functional property can be defined for datatype properties. In OWL DL object properties and datatype properties are disjoint, so an inverse-functional property cannot be defined for datatype properties. See also Sec. 8.1 and Sec. 8.2." (thinking aloud here...) So to create an inverse functional Datatype property for OWL Full ontology from this meta model, one will have to declare that property as both inverse function and as datatype. As inverse functional prop is in turn an object property... the prop is both a datatype and object property => which is consistent with RDF and OWL-Full semantics. Granted. No issue. But perhaps to include some explanation to reassure the reader that the semantics is correct with reference to WebOnt reference? 12.6 Datatypes Perhaps to explicitly mention that the OWL's notion of unsupported type is automatically handled too? Doesn't need much description, as TypedLiteral and the RDFDatatype are already described in the RDFMetaModel. Again, this is more like just covering all OWL constructs like a checklist in this chapter rather than just leaving it implied in the TypedLiteral section. 12.2.3 RDFSLiteral This section seems out of place and interrupted the flow. Perhaps move to before or after 12.3.15 TypedLiteral? 12.3 Class descriptions The alphabetical ordering of the sections on various annonymous classes: "ComplementClass, Enumerated, Intersection, Restriction, Union", could perhaps be arranged from simple (complement, intersection, union) to complex ideas (restriction)? It was slightly interrupting reading Intersection, then a detail long Restriction section, then back to Union, which carries similar content to Intersection. Typos ----- 12.1 "Vendors who are interested in supporting OWL Lite would simply use only the relevant constructs from the base package and tighted a few constraints from the OWL DL package, as required." Change "tighted" to "tighten" perhaps? [1] http://www.omg.org/cgi-bin/doc?ad/05-09-08.pdf [2] http://lists.w3.org/Archives/Public/public-swbp-wg/2005Nov/0174
Received on Monday, 16 January 2006 11:25:03 UTC