File organizations and access methods for CLV disks

Abstract

A large and important class of optical disc technology are CLV format discs such as CD ROM and WORM. In this paper, we examine the issues related to the implementation and performance of several different file organizations on CLV format optical discs such as CD ROM and WORM. The organizations examined are based on hashing and trees. The CLV recording scheme is shown to be a good environment for efficiently implementing hashing. Single seek access and storage utilization levels approaching 100% can be achieved for CD ROM's. It is shown that a B-tree organization is not a good choice for WORM discs (both CAV and CLV), but a modified ISAM approach can be appropriate for WORM discs. We describe clustered BIM's, a class of tree organizations appropriate for CD ROMS. Expressions for the expected retrieval performance of both hashing and trees are also given. The paper concludes by outlining recent results and future directions on buffered implementations of access methods for WORM discs, as well as advantages of signature based access methods for text retrieval in WORM disc architectures.