Computer Laboratory

Technical reports

Decomposing file data into discernible items

Calicrates Policroniades-Borraz

August 2006, 230 pages

This technical report is based on a dissertation submitted December 2005 by the author for the degree of Doctor of Philosophy to the University of Cambridge, Hughes Hall.

Abstract

The development of the different persistent data models shows a constant pattern: the higher the level of abstraction a storage system exposes the greater the payoff for programmers. The file API offers a simple storage model that is agnostic of any structure or data types in file contents. As a result, developers employ substantial programming effort in writing persistent code. At the other extreme, orthogonally persistent programming languages reduce the impedance mismatch between the volatile and the persistent data spaces by exposing persistent data as conventional programming objects. Consequently, developers spend considerably less effort in developing persistent code.

This dissertation addresses the lack of ability in the file API to exploit the advantages of gaining access to the logical composition of file content. It argues that the trade-off between efficiency and ease of programmability of persistent code in the context of the file API is unbalanced. Accordingly, in this dissertation I present and evaluate two practical strategies to disclose structure and type in file data.

First, I investigate to what extent it is possible to identify specific portions of file content in diverse data sets through the implementation and evaluation of techniques for data redundancy detection. This study is interesting not only because it characterises redundancy levels in storage systems content, but also because redundant portions of data at a sub-file level can be an indication of internal file data structure. Although these techniques have been used by previous work, my analysis of data redundancy is the first that makes an in-depth comparison of them and highlights the trade-offs in their employment.

Second, I introduce a novel storage system API, called Datom, that departs from the view of file content as a monolithic object. Through a minimal set of commonly-used abstract data types, it discloses a judicious degree of structure and type in the logical composition of files and makes the data access semantics of applications explicit. The design of the Datom API weighs the addition of advanced functionality and the overheads introduced by their employment, taking into account the requirements of the target application domain. The implementation of the Datom API is evaluated according to different criteria such as usability, impact at the source-code level, and performance. The experimental results demonstrate that the Datom API reduces work-effort and improves software quality by providing a storage interface based on high-level abstractions.

Full text

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BibTeX record

@TechReport{UCAM-CL-TR-672,
  author =	 {Policroniades-Borraz, Calicrates},
  title = 	 {{Decomposing file data into discernible items}},
  year = 	 2006,
  month = 	 aug,
  url = 	 {http://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-672.pdf},
  institution =  {University of Cambridge, Computer Laboratory},
  number = 	 {UCAM-CL-TR-672}
}