12.3 OWL Use Cases and Requirements
12.3 OWL Use Cases and Requirements
As with most W3C efforts, you can track the progress of work within any one activity by the state and version of the documents released. The first document released by the WebOnt
The roots for OWL exist in the OWL Use Cases and Requirements document, released in July 2002 and recently updated. According to this document, we've been working with ontologies all along by using vocabularies such as ones I've used in the book like Dublin Core and PostCon. These are ontologies because they define the data for a specific knowledge domain, which is what the Use Case and Requirements document defines as ontology. Specifically, ontology encompasses four concepts:
When you consider that these concepts can be used, equally, with RDF and RDFS, you can see why there is some confusion about where RDFS ends and OWL begins. The Use Cases document, while demonstrative of applications facilitated by the use of an ontology, didn't exactly help with clarifying when to use OWL and when to use RDFS, other than suggesting use of RDFS for defining OWL and then using OWL for everything else.
In addition to use cases, design goals given in the document were:
None of the use cases or design goals is overwhelmingly complex, except possibly testing for inconsistencies. The
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12.4 OWL SpecificationsOWL has no shortage of associated documents:
We just
After reviewing the use cases and requirements
12.4.1 OWL Guide 1.0
A further
This is an important point. XML Schemas and message-based uses of XML focus on specific pieces of data and specific uses of data, such as sending a message and processing its results. Nothing within basic XML or within the XML Schema allows one to derive information outside of the context of the specific use. For instance, the tool I used to maintain a weblog might support SOAP requirements that allow me to publish a new posting, but nothing associated with the SOAP request allows me, or
The guide provides an overview of three different types of OWL:
These specific designations have more to do with what certain tools can and will support, which of course influences the design and implementation of a specific ontology. Looking at PostCon's RDFS definition, PostCon could be ported to an ontology, with any restrictions and constraints added to it fitting comfortably within those allowed by OWL DL.
The rest of the guide then covers the basic
12.4.2 OWL Reference 1.0The OWL Reference document provides the formal specification of the language. It is equivalent to the XML specification for RDF/XML covered in Chapter 3 and Chapter 4. However, unlike the RDF document, the OWL documents are a work in progress and far from complete. The section of most interest in the reference is the one covering the language structure. Unlike RDF, the OWL vocabulary is quite large. Like RDF, though, it makes use of elements from RDFS (and from RDF).
The Reference document breaks the structure of OWL down into separate components, most of which are already familiar to you from previous chapters, such as the concepts of classes, properties, and enumerations (collections). Section 12.5 provides an overview of these items. However, OWL also has several concepts unique to it, such as the Boolean combination of class expressions and property restrictions, which add the additional layer of reasoning you would expect for a language defining a business domain. These
You'll sometimes find reference to
owl:Thing
in the document, but it doesn't show in any formal definition of elements, though it is listed as a
12.4.3 OWL Abstract Syntax and Semantics
The Abstract Syntax and Semantics document provides a breakdown of the model theoretical axioms and rules guiding the implementation and interpretation of OWL. It provides a semantic definition of what is a "fact" within OWL, as well as a high-level overview of how OWL differs from DAML+OIL and how OWL Lite differs from the
A major difference between OWL and OWL Lite is the inclusion of what the document calls OWL descriptions. The formal definition of a description is:
< description> ::= <classID>
<restriction>
unionOf( {<description>} )
intersectionOf( {<description>} )
complementOf( <description> )
oneOf({<individualID>} )
Primarily, an OWL description is one of a class identifier, a property restriction, or a complex class association. These descriptions enhance the reasoning inherent within OWL ontology ”reasoning that goes beyond that allowed in RDFS. Regarding the separation of OWL and OWL Lite in this chapter, for the most part Section 12.5 applies to both OWL and OWL Lite, though the data typing discussed in the section is beyond OWL Lite. Additionally, the property restrictions covered in "Bits of Knowledge: More Complex OWL Constructs" apply to both. However, the discussion about complex classes in this section applies purely to the fully featured OWL, as these make up most of the options from the OWL description just provided.
Another section in the Abstract document, "RDFS-Compatible Model-
12.4.4 Feature Synopsis for OWL Lite and OWL
The Feature Synopsis document provides a summary of features for OWL and OWL Lite. It makes a good "in a
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