Encyclopedia of Database Systems

2018 Edition
| Editors: Ling Liu, M. Tamer Özsu


  • Evaggelia PitouraEmail author
Reference work entry
DOI: https://doi.org/10.1007/978-1-4614-8265-9_873


Cursor; Iterator; Synchronous pipelines


In general terms, a physical operator is an implementation of a relational operator. For a relational operator, there are many alternative physical operators that implement it, for instance, sort-merge and hash-join provide alternative algorithms for implementing join. The query execution engine provides generic implementations of all physical operators. Typically, each physical operator supports a uniform iterator interface that hides any internal implementation details and allows operators to be combined together. The iterator interface includes the functions: (i) open() that prepares an operator to produce data, (ii) next() that produces an output tuple, and (iii) close() that performs the final bookkeeping.

Key Points

During query processing, an input query is transformed to a plan to be executed by the query execution engine. An execution plan can be thought of as a dataflow graph where the nodes correspond to the...

This is a preview of subscription content, log in to check access.

Recommended Reading

  1. 1.
    Graefe G. Query evaluation techniques for large databases. ACM Comput Surv. 1993;25(2):73–170.CrossRefGoogle Scholar
  2. 2.
    Hellerstein JM, Stonebraker M, Hamilton J. Architecture of a database system. Found Trends Databases. 2007;1(2):141–259.zbMATHCrossRefGoogle Scholar
  3. 3.
    Ramakrishnan R, Gehrke J. Database management systems. New York: McGraw-Hill; 2003.zbMATHGoogle Scholar

Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Department of Computer Science and EngineeringUniversity of IoanninaIoanninaGreece

Section editors and affiliations

  • Evaggelia Pitoura
    • 1
  1. 1.Dept. of Computer ScienceUniv. of IoanninaIoanninaGreece