
Query by Example (QBE) is a
database
In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases spa ...
query language
Query languages, data query languages or database query languages (DQL) are computer languages used to make queries in databases and information systems. A well known example is the Structured Query Language (SQL).
Types
Broadly, query language ...
for
relational database
A relational database is a (most commonly digital) database based on the relational model of data, as proposed by E. F. Codd in 1970. A system used to maintain relational databases is a relational database management system (RDBMS). Many relatio ...
s. It was devised by
Moshé M. Zloof at
IBM Research
IBM Research is the research and development division for IBM, an American multinational information technology company headquartered in Armonk, New York, with operations in over 170 countries. IBM Research is the largest industrial research or ...
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. Originally limited only for the purpose of
retrieving data, QBE was later extended to allow other operations, such as inserts, deletes and updates, as well as creation of temporary tables.
The motivation behind QBE is that a
parser
Parsing, syntax analysis, or syntactic analysis is the process of analyzing a string of symbols, either in natural language, computer languages or data structures, conforming to the rules of a formal grammar. The term ''parsing'' comes from Lati ...
can convert the user's actions into statements expressed in a database manipulation language, such as
SQL. Behind the scenes, it is this statement that is actually executed. A suitably comprehensive front-end can minimize the burden on the user to remember the finer details of SQL, and it is easier and more productive for end-users (and even programmers) to select tables and columns by selecting them rather than typing in their names.
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
ee search by multiple examples Similarity search is based comparing document vectors (see
Vector Space Model
Vector space model or term vector model is an algebraic model for representing text documents (and any objects, in general) as vectors of identifiers (such as index terms). It is used in information filtering, information retrieval, indexing and ...
).
QBE represents seminal work in
end-user development
End-user development (EUD) or end-user programming (EUP) refers to activities and tools that allow end-users – people who are not professional software developers – to program computers. People who are not professional developers can use EUD ...
, 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
Microsoft Access is a database management system (DBMS) from Microsoft that combines the relational Access Database Engine (ACE) with a graphical user interface and software-development tools (not to be confused with the old 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
An object database or object-oriented database is a database management system in which information is represented in the form of objects as used in object-oriented programming. Object databases are different from relational databases which are ...
(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
In database theory, relational algebra is a theory that uses algebraic structures with a well-founded semantics for modeling data, and defining queries on it. The theory was introduced by Edgar F. Codd.
The main application of relational algebra ...
.
Example
An example using the
Suppliers and Parts database is given here to illustrate how QBE works.
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.
For
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.
Another approach to text comparisons is to allow one or more
wildcard character
In software, a wildcard character is a kind of placeholder represented by a single character, such as an asterisk (), which can be interpreted as a number of literal characters or an empty string. It is often used in file searches so the full n ...
characters. For example, if an asterisk is designated as a wild wildcard character in a particular system, then searching for last names using "Rob*" would return (match) last names such as "Rob", "Robert", "Robertson", "Roberto", etc.
See also
*
CRUD
*
Microsoft Query by Example
*
GraphQL a QBE for JSON front-ends.
*
QBIC
References
Sources
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External links
*
* {{Cite web , url= http://www.ahmetsoylu.com/wp-content/uploads/soylu_UAIS_2016.pdf , format= PDF , title= Experiencing OptiqueVQS: a multi-paradigm and ontology-based visual query system for end users , first1= Ahmet , last1= Soylu , first2= Martin , last2= Giese , first3= Ernesto , last3= Jimenez-Ruiz , first4= Guillermo , last4= Vega-Gorgojo , first5= Ian , last5= Horrocks , date= 2015 , quote= Visual Query System (VQS) , doi= 10.1007/s10209-015-0404-5
Relational model
Query languages
Human–computer interaction
1970s software
IBM software