Query by Example

shaf is well kewl In the context of information retrieval, QBE has a somewhat different meaning. The user can submit a document, or several documents, and ask for "similar" documents to be retrieved from a document database. Similarity search is based comparing document vectors (see Vector Space Model).

QBE is a seminal work in end-user development, frequently cited in research papers as an early example of this topic.

Currently, QBE is supported in several relational database front ends, notably Microsoft Access, which implements "Visual Query by Example", as well as Microsoft SQL Server Enterprise Manager. It is also implemented in several object-oriented databases (e.g. in db4o).

QBE is based on the logical formalism called tableau query, although QBE adds some extensions to that, much like SQL is based on the relational algebra.

Example

An example using the Suppliers and Parts database is given here to illustrate how QBE works. File:QBESampleTable2.jpg

As a general technique

The term also refers to a general technique influenced by Zloof's work whereby only items with search values are used to "filter" the results. It provides a way for a software user to perform queries without having to know a query language (such as SQL). The software can automatically generate the queries for the user (usually behind the scenes). Here are some examples:

Example Form B:

.....Name: Bob
..Address:
.....City:
....State: TX
..Zipcode:

Resulting SQL:

SELECT * FROM Contacts WHERE Name='Bob' AND State='TX'

Note how blank items do not generate SQL terms. Since "Address" is blank, there is no clause generated for it.

Example Form C:

.....Name: 
..Address:
.....City: Sampleton
....State: 
..Zipcode: 12345

Resulting SQL:

SELECT * FROM Contacts WHERE City='Sampleton' AND Zipcode='12345'

More advanced versions of QBE have other comparison operator options, often via a pull-down menu, such as "Contains", "Not Contains", "Starts With", "Greater-Than", and so forth.

See also

• Microsoft Query by Example

Sources

• Zloof, Moshé M (May 1975), "Query by Example", NCC (proceedings), vol. 44, Anaheim, CA, US: AFIPS.
• Ramakrishnan, Raghu; Gehrke, Johannes, "6. QBE", Database Management Systems (PDF) (3rd ed.), Wisc.
• Date, Christopher ‘Chris’ J (2004), "8. Relational Calculus", An Introduction to Database Systems, Addison‐Wesley Pearson, pp. 242–7, ISBN 0-321-18956-6.
• Oracle Definitions, Tech target.
• Zaiane, "5", CC 354 notes, CA: SFI.

External links

• Query by Example for PostgreSQL, Pg foundry.
• "Query by Example in Java using Hibernate", Jboss.
• "Experiencing OptiqueVQS: a multi-paradigm and ontology-based visual query system for end users", Optique (PDF).