Encyclopedia of Database Systems

2009 Edition

Indexed Sequential Access Method

  • Alex Delis
  • Vassilis J. Tsotras
Reference work entry
DOI: https://doi.org/10.1007/978-0-387-39940-9_738


Indexed sequential file; ISAM file; ISAM


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. 1.
    Bayer R. and McCreight E. Organization and maintenance of large ordered indexes. Acta Inf., 1(3):173–183, 1972.CrossRefGoogle Scholar
  2. 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.Google Scholar
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    IBM Corporation. IBM System/360 Operating System Data Management Services, February 1972. Second Edition, C26-3746-1.Google Scholar
  4. 4.
    Keehn D.G. and Lacy S.O. VSAM Data set design parameters. IBM Syst. J. 13(3):186–212, 1974.Google Scholar
  5. 5.
    Larson P. Analysis of index-sequential files with overflow chaining. ACM Trans. Database Syst., 6(4):671–680, 1981.MathSciNetCrossRefGoogle Scholar
  6. 6.
    Mullin J.K. An improved index sequential access method using hashed overflow. Commun. ACM, 15(5):301–307, May 1972.CrossRefzbMATHGoogle Scholar
  7. 7.
    Wong K.F. and Strauss J.G. An analysis of ISAM performance improvement options. Manag. Datamat. J., 4(3):95–107, 1975.Google Scholar

Copyright information

© Springer Science+Business Media, LLC 2009

Authors and Affiliations

  • Alex Delis
    • 1
  • Vassilis J. Tsotras
    • 2
  1. 1.University of AthensAthensGreece
  2. 2.University of California-RiversideRiversideUSA