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have been clustered as clustered files. I have gone to some pains to avoid the use of this terminology because of the conceptual difference that exists between a structure which is inherent in the data and can be discovered by clustering, and an organisation of the data to facilitate its manipulation inside a computer. Unfortunately this distinction becomes somewhat blurred when clustering techniques are used to generate a physical organisation of data. For example, the work by Bell et al.[52] is of this nature. Furthermore, it has recently become popular to cluster records simply to improve the efficiency of retrieval. Buckhard and Keller[53] base the design of a file structure on maximal complete subgraphs (or cliques). Hatfield and Gerald[54] have designed a paging algorithm for a virtual memory store based on clustering. Simon and Guiho[55] look at methods for preserving 'clusters' in the data when it is mapped onto a physical storage device.

Some of the work that has been largely ignored in this chapter, but which is nevertheless of importance when considering the implementation of a file structure, is concerned directly with the physical organisation of a storage device in terms of block sizes, etc. Unfortunately, general statements about this are rather hard to make because the organisation tends to depend on the hardware characteristics of the device and computer. Representative of work in this area is the paper by Lum et al.[56].

References

1. HSIAO, D. and HARARY, F., 'A formal system for information retrieval from files', Communications of the ACM, 13, 67-7 3 ( 1970)

2. ROBERTS, D. C., 'File organization techniques', Advances in Computers, 12, 115-174 (1972)

3. BERTZISS, A. T., Data Structures: Theory and Practice, Academic Press, London and New York (1971)

4. DODD, G. G., 'Elements of data management systems', Computing Surveys, 1, 117-133 (1969)

5. CLIMENSON, W. D., 'File organization and search techniques', Annual Review of Information Science and Technology, 1, 107-135 ( 1966)

6. WARHEIT, 1. A., 'File organization of library records', Journal of Library Automation, 2, 20-30 (1969)

7. PRYWES, N. S. and SMITH, D. P., 'Organization of information', Annual Review of Information Science and Technology, 7, 103-158 (1972) Technology, 7,103 158 (1972)

8. CODD, E. E., 'A relational model of data for large shared data banks', Communications of the A CM, 13, 377-387 ( 1970)
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