The general intent of this proposal is to extend OWL DL, and thus to use OWL constructs wherever possible.
If users are making extensive use of rules, they may want to restrict the form or expressiveness of the rules they employ, in order to increase interoperability, reusability, extensibility, computational scaleability, or ease of implementation.
A useful restriction in the form of the rules is to limit antecedent and consequent classAtoms to be named classes, where the classes are defined purely in OWL (in the same document or in external OWL documents). Adhering to this format makes it easier to translate rules to or from existing (or future) rule systems, including:
Adhering to this form also maximises reuse and interoperability of the ontology knowledge in the rules with other OWL-speaking systems that do not necessarily support SWRL.
Users also may want to restrict the expressiveness of the OWL classes and descriptions appearing in rules. One useful restriction on expressivity is Description Logic Programs [Grosof et al 2003] which, e.g., prohibits existentially-quantified knowledge in consequents. Suitably-restricted SWRL rules can be straightforwardly extended to enable procedural attachments and/or nonmonotonic reasoning (negation-as-failure and/or prioritised conflict handling) of the kinds supported in CCI rule systems and in RuleML [RuleML] which facilitates interoperability between those CCI rule systems. Such adherence may thus facilitate combining SWRL knowledge with knowledge from those other rules languages. Suitable restrictions can also improve the empirical tractability of reasoning with rules.
A longer, more detailed version of the above usage suggestions and cautions is available at http://www.daml.org/listarchive/joint-committee/1491.html.