Query by Example

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Query by Example (QBE) is a database query language for relational databases. It was devised by Moshé M. Zloof at IBM Research during the mid 1970s, in parallel to the development of SQL. It is the first graphical query language, using visual tables where the user would enter commands, example elements and conditions. Many graphical front-ends for databases use the ideas from QBE today.

Based on the notion of Domain relational calculus, QBE can be used as a search tool as well. A QBE parser parses the search query and looks for the keywords while eliminating words like a, an or the. A more formal query string, in languages such as SQL, is then generated, which is finally executed. However, when compared with a formal query, the results in the QBE system will be more variable. The user can also search for similar documents based on the text of a full document that he or she may have. This is accomplished by the user’s submission of documents (or numerous documents) to the QBE results template. The analysis of these document(s) the user has inputted via the QBE parser will generate the required query.

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[edit] Example

A simple example using the Suppliers and Parts database is given here, just to give you a feel for how QBE works.

Image:QBESampleTable2.jpg

[edit] See also

[edit] References

  • M. Zloof. Query by Example. AFIPS, 44, 1975.
  • Raghu Ramakrishnan, Johannes Gehrke. Database Management Systems 3rd edition. Chapter 6.
  • Date, C.J. (2004). "8 Relational Calculus", in Maite Suarez-Rivas; Katherine Harutunian: An Introduction to Database Systems. Pearson Education Inc.. ISBN 0-321-18956-6. 

[edit] Sources

[edit] External links

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