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The following rules MUST be followed when using this document; these are taken from IETF RFC 2119 (simplified):

1. MUST: This word means that the definition is an absolute requirement of the specification.

2. MUST NOT: This phrase means that the definition is an absolute prohibition of the specification.

3. SHOULD: This word means that there may exist valid reasons in particular circumstances to ignore a particular item, but the full implications MUST be understood and carefully weighed before choosing a different course.

4. SHOULD NOT: This phrase means that there may exist valid reasons in particular circumstances when the particular behavior is acceptable or even useful, but the full implications should be understood and the case carefully weighed before implementing any behavior described with this label.

5. MAY: This word means that an item is truly optional. One user may choose to include the item because a particular marketplace requires it or because the vendor feels that it enhances the product, while another vendor may omit the same item.

Overview

There are normative and non-normative property chains. This document concerns Property Chains that are part of the normative specification and are included in the ontology file. The normative property chains have side effects on other parts of the ontology and restrict the use of cardinality constraints [1]. They should be used sparingly and need review by the larger Technical Oversight Board (TOB) before they are added to the ontology to approve their use and weigh the need for cardinality constraints.

Property chains are considered complex properties in OWL DL. The same is true of transitive properties, as another example. To ensure reasoning is completed in some period of time, the OWL language does not allow cardinality constraints with complex properties. A complete list is available in the OWL structural specification in clause 11.2, at OWL 2 Web Ontology Language Structural Specification and Functional-Style Syntax (Second Edition).

This document prescribes the preliminary process for using property chains and the rules we MUST follow. The Architecture WG will amend this document as we implement scenarios and test cases with property chains and transitive relationships.

[1] Qualified cardinality restrictions (QCRs) OWL restrictions

Rules

• Property chains SHOULD be used sparingly since they preclude the use of cardinality constraints.

• If a property chain is part of the normative ontology, it MUST be placed in the main ontology file.

• If it is not normative, the property chain MUST be placed in the addenda, where users can choose to import the ontology into their application.

• The ontology working group and the TOB MUST decide what is normative and non-normative.

Voting