OWL Language features:
general line of attack & a first sketch

Frank van Harmelen
Ian Horrocks


This short note (about 2 pgs) is meant to set the direction for the discussion on language features.

CONTENTS

SUMMARY

  1. OWL should have a frame-style part (for easy idiomatic usage) as well as a DAML+OIL/DL-style axiomatic part (for high expressiveness)
  2. The frame-part would consist of (roughly):
  3. The axiomatic part would be close to DAML+OIL expressiveness and include (again roughly):

LANGUAGE FEATURES, NOT SYNTAX:

The focus group should discuss first which features/expressiveness/constructs OWL should have. This discussion should be separate from what syntactic form each of these should have, or even the specific syntactic form of the language as a whole. Syntax can be designed last, not first. Actually, we expect that a single syntax won't do. We will need at least two: one RDF-based syntax (for machines) and one presentation syntax readable for humans (taking lesson from OIL), and probably also an XML-DTD based syntax.

DISTINGUISH LANGUAGE CONSTRUCTIONS FROM THE UNDERLYING LOGIC.

The language constructions should provide good support for idiomatic expressions that occur often in practice; the underlying logic consists of (typically much smaller) atomic constructions with nice mathematical properties. Of course, the idioms should be translatable into the logic.

Examples of such idiom are:

Translation of these idioms into the logic might result in e.g. OWL should have a stronger idiomatic vocabulary than DAML+OIL (which already has some, but not much)

LOW THRESHOLD, HIGH CEILING

On the one hand, we want to make a language that is easy to use for most, on the other hand we don't want to limit the sophistication of some. This could be achieved by a better separation of things that are easy from things that are hard.

Note: easy/hard refers to "easy to understand by our target group", perhaps also to "easy to implement in a variety of tools" (editors, storage, browser/visualisors), and least of all to "low complexity class for a reasoner") In fact it is quite possible that the "easy" part of the language might formally have the same expressive power and complexity as the full language.

A first stab:

The following are considered "easy":

The following are considered "hard":

FRAMES VS. AXIOMS

One way of obtaining "low threshold, high ceiling" is to have two parts to the language: a frame-based part, and an axiom-based part (for want of a better term).

RELATION TO DAML+OIL

The above proposal takes DAML+OIL as its basis (as per our charter). The expressiveness of OWL will be close (if not: equal) to DAML+OIL. The aove proposal extends DAML+OIL in order to provide a lower step-in threshold (which is perceived to be too high for DAML+OIL). Another extension is to provide a human-readable presentation syntax besides an RDF/XML-based syntax.

NEXT STEPS TO TAKE: