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Indexed Sequential Access Method

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Encyclopedia of Database Systems

Synonyms

Indexed sequential file; ISAM file; ISAM

Definition

An indexed sequential access method is a static, hierarchical, disk-based index structure that enables both (single-dimensional) range and membership queries on an ordered data file. The records of the data file are stored in sequential order according to some data attribute(s). Since ISAM is static, it does not change its structure if records are added or deleted from the data file. Should new records be inserted into the data file, they are stored in an overflow area. Deleted records are removed from the file (leaving empty space).

Historical Background

Although transparent for the user of a DBMS, access methods play a key role in database performance. A major performance goal of a DBMS is to minimize the number of I/Os (i.e., blocks or pages transferred) between the disk and main memory. One way to achieve this goal is to minimize the number of I/Os when answering queries. Note that many queries reference only a small...

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Recommended Reading

  1. Bayer R. and McCreight E. Organization and maintenance of large ordered indexes. Acta Inf., 1(3):173–183, 1972.

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  2. Behymer J.A., Ogilive R.A., and Merten A.G. Analysis of indexed sequential and direct access file organizations. In Proc. 1974 ACM SIGFIDET (SIGMOD) Workshop on Data Description, Access and Control, 1974, pp. 186–212.

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  3. IBM Corporation. IBM System/360 Operating System Data Management Services, February 1972. Second Edition, C26-3746-1.

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  4. Keehn D.G. and Lacy S.O. VSAM Data set design parameters. IBM Syst. J. 13(3):186–212, 1974.

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  5. Larson P. Analysis of index-sequential files with overflow chaining. ACM Trans. Database Syst., 6(4):671–680, 1981.

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  6. Mullin J.K. An improved index sequential access method using hashed overflow. Commun. ACM, 15(5):301–307, May 1972.

    Article  MATH  Google Scholar 

  7. Wong K.F. and Strauss J.G. An analysis of ISAM performance improvement options. Manag. Datamat. J., 4(3):95–107, 1975.

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Author information

Authors and Affiliations

  1. University of Athens, Athens, Greece

    Alex Delis

  2. University of California-Riverside, Riverside, CA, USA

    Vassilis J. Tsotras

Authors
  1. Alex Delis
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  2. Vassilis J. Tsotras
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Editor information

Editors and Affiliations

  1. College of Computing, Georgia Institute of Technology, 266 Ferst Drive, 30332-0765, Atlanta, GA, USA

    LING LIU (Professor) (Professor)

  2. Database Research Group David R. Cheriton School of Computer Science, University of Waterloo, 200 University Avenue West, N2L 3G1, Waterloo, ON, Canada

    M. TAMER ÖZSU (Professor and Director, University Research Chair) (Professor and Director, University Research Chair)

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© 2009 Springer Science+Business Media, LLC

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Delis, A., Tsotras, V. (2009). Indexed Sequential Access Method. In: LIU, L., ÖZSU, M.T. (eds) Encyclopedia of Database Systems. Springer, Boston, MA. https://doi.org/10.1007/978-0-387-39940-9_738

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