An RDF query language is a

computer language A computer language is a formal language used to communicate with a computer. Types of computer languages include: * Software construction#Construction languages, Construction language – all forms of communication by which a human can Comput ...

, specifically a

query language A query language, also known as data query language or database query language (DQL), is a computer language used to make queries in databases and information systems. In database systems, query languages rely on strict theory to retrieve informa ...

for

database In computing, a database is an organized collection of data or a type of data store based on the use of a database management system (DBMS), the software that interacts with end users, applications, and the database itself to capture and a ...

s, able to retrieve and manipulate data stored in

Resource Description Framework The Resource Description Framework (RDF) is a method to describe and exchange graph data. It was originally designed as a data model for metadata by the World Wide Web Consortium (W3C). It provides a variety of syntax notations and formats, of whi ...

(RDF) format. SPARQL has emerged as the standard RDF query language, and in 2008 became a

W3C recommendation The World Wide Web Consortium (W3C) is the main international standards organization for the World Wide Web. Founded in 1994 by Tim Berners-Lee, the consortium is made up of member organizations that maintain full-time staff working together in ...

Query language properties

Properties relevant to RDF query language design include support for the RDF format: * Support for RDF data, which is a collection of triples that form the RDF graph * Support for RDF semantics and inference that allows for entailment, the reasoning about the meaning of RDF graphs * Support for schema data types, such as

XML schema An XML schema is a description of a type of XML document, typically expressed in terms of constraints on the structure and content of documents of that type, above and beyond the basic syntactical constraints imposed by XML itself. These constrai ...

and for desirable language features: * Expressiveness: the power of query expression that may be constructed * Closure: data operations on an RDF graph should result in another RDF graph * Orthogonality: data operations are independent of the context in which they are used * Safety: every expression returns a finite set of results.

Query language families

RDF query languages can be grouped into language families, each family comprising a set of closely related languages. The SPARQL family of languages includes SquishQL, RDQL, SPARQL, and TriQL. These languages treat RDF data stores as triple stores that do not necessarily have ontology or schema information associated with them. Members of the SPARQL family are considered relational query languages because they have relational or pattern-based operations. SquishQL was a language constructed to be easy to use and similar in structure to SQL. RDQL, an acronym for RDF Data Query Language, was a further development of SquishQL. RDQL was intended to be a simple low level RDF language and was at one point a candidate for W3C standardization. SPARQL is an extension of RDQL that supports extraction of RDF subgraphs. In 2008, SPARQL 1.0 became a W3C recommendation and SPARQL 1.1 became a W3C recommendation in 2013. The RQL family of languages includes RQL, SeRQL, and eRQL. These languages support querying of both data and schema. RQL, an acronym for RDF Query Language, is known for using types defined in RDF schemas (RDFS) to query the schema class hierarchy and to support data querying by type. RQL is considered more expressive than the SPARQL family of languages, but has been criticized for too many features and unusual syntactic constructs. SeRQL and eRQL were developed as simplified alternatives to RQL. There is a family of RDF query languages inspired by XML query technology. XQuery for RDF uses the XML query language

XQuery XQuery (XML Query) is a query language and functional programming language designed to query and transform collections of structured and unstructured data, primarily in the form of XML. It also supports text data and, through implementation-sp ...

to query RDF data by serializing RDF into an XML format and then using XQuery on the result; this has been called the "syntactic web approach". TreeHugger and RDF Twig use

XSLT XSLT (Extensible Stylesheet Language Transformations) is a language originally designed for transforming XML documents into other XML documents, or other formats such as HTML for web pages, plain text, or XSL Formatting Objects. These formats c ...

to query RDF data. Versa by 4Suite is a query language that drew inspiration from

XPath XPath (XML Path Language) is an expression language designed to support the query or transformation of XML documents. It was defined by the World Wide Web Consortium (W3C) in 1999, and can be used to compute values (e.g., strings, numbers, or ...

. There exist RDF query languages based on other principles. Metalog combines querying with reasoning and has an English like syntax. Algae is a query language developed by the W3C that adds reactive rules, also called actions, that determine for instance whether an Algae expression is a data query or a data update. Other examples of RDF Query languages include RDFDBQL.

Example

select ?uri,?name, ?lat, ?lon from where (?city, , ?name), (?city, ,?uri), (?city, , ?lat), (?city, , ?lon) using rdfs FOR , pos FOR , doilair FOR , vcard FOR

Related languages

Other languages which can query RDF data include: * DQL,

XML Extensible Markup Language (XML) is a markup language and file format for storing, transmitting, and reconstructing data. It defines a set of rules for encoding electronic document, documents in a format that is both human-readable and Machine-r ...

-based, queries and results expressed in DAML+OIL * XUL has
template
element in which to declare rules for matching data in RDF. XUL uses RDF extensively for databinding. *

Adenine Adenine (, ) (nucleoside#List of nucleosides and corresponding nucleobases, symbol A or Ade) is a purine nucleotide base that is found in DNA, RNA, and Adenosine triphosphate, ATP. Usually a white crystalline subtance. The shape of adenine is ...

(programming language written in RDF).

, or XML Query, is a standard query language for XML documents. Graph query languages, such as

Cypher Query Language Cypher is a declarative graph query language that allows for expressive and efficient data querying in a property graph. Cypher was largely an invention of Andrés Taylor while working for Neo4j, Inc. (formerly Neo Technology) in 2011. Cypher wa ...

, GraphQL, and

Gremlin A gremlin is a mischievous fictional creature invented at the beginning of the 20th century to originally explain malfunctions in aircraft, and later in other machinery, processes, and their operators. Depictions of these creatures vary widely. ...

, are designed to query

graph database A graph database (GDB) is a database that uses graph structures for semantic queries with nodes, edges, and properties to represent and store data. A key concept of the system is the graph (or edge or relationship). The graph relates the dat ...

s, of which RDF data stores are an example. The Topic Map Query Language (TMQL) is a query language for

topic maps A topic map is a standard for the representation and interchange of knowledge, with an emphasis on the findability of information. Topic maps were originally developed in the late 1990s as a way to represent back-of-the-book index structures ...

, a data representation similar to but more general than RDF.

References

External links

RDF Query specification

RDF query language survey
*
A Comparison of (some) RDF Query Languages

RDF query use cases, including query language samples

SparQL
{{Query languages RDF data access Resource Description Framework Query languages