Proposals for OrderingKey DS instantiation in MPEG-7 description

This document identifies some solutions to the problem stated in the Editor’s Note in clause 7.7.1.1 of the MDS Study of CD, document ISO/IEC JTC 1/SC 29/WG 11/N3816. Therefore this document is intended as a contribution to the MDS group. Presently there is no way to instantiate an Ordering Key DS within a “valid” MPEG-7 description. To solve this problem three proposals are here considered and their respective implication are discussed. The first proposal is to derive the OrderingKeyType as an extension of the HeaderType allowing the instantiation, at the header level, of any MPEG-7 Complete/Unit Description and DSType instances. The second solution is to include the OrderingKey DS as a component of the BasicDescriptionType. This allows to apply the ordering tool only in an MPEG-7 Complete Description, but no Unit Description. The third solution is to adopt both the first and second proposals. In Section 2 the three solutions are detailed and the required modification in terms of syntax and usage are discussed. In Section 3 the three solutions are compared.