Resource Description Framework
The Resource Description Framework (RDF) is a method to describe and exchange
RDF is a directed graph composed of triple statements. An RDF graph statement is represented by: (1) a node for the subject, (2) an arc from subject to object, representing a predicate, and (3) a node for the object. Each of these parts can be identified by a Uniform Resource Identifier (URI). An object can also be a literal value. This simple, flexible data model has a lot of expressive power to represent complex situations, relationships, and other things of interest, while also being appropriately abstract.
RDF was adopted as a W3C recommendation in 1999. The RDF 1.0 specification was published in 2004, and the RDF 1.1 specification in 2014. SPARQL is a standard query language for RDF graphs. RDF Schema (RDFS), Web Ontology Language (OWL) and SHACL (Shapes Constraint Language) are ontology languages that are used to describe RDF data.
Overview
The RDF data model
For example, one way to represent the notion "The sky has the color blue" in RDF is as the triple: a
RDF is an abstract model with several serialization formats (being essentially specialized file formats). In addition the particular encoding for resources or triples can vary from format to format.
This mechanism for describing resources is a major
A collection of RDF statements intrinsically represents a
As
upon RDF.History
The initial RDF design, intended to "build a vendor-neutral and operating system- independent system of metadata",
A first public draft of RDF appeared in October 1997,[5][6] issued by a W3C working group that included representatives from IBM, Microsoft, Netscape, Nokia, Reuters, SoftQuad, and the University of Michigan.[3]
In 1999, the W3C published the first recommended RDF specification, the Model and Syntax Specification ("RDF M&S").[7] This described RDF's data model and an XML serialization.[8]
Two persistent misunderstandings about RDF developed at this time: firstly, due to the MCF influence and the RDF "Resource Description" initialism, the idea that RDF was specifically for use in representing metadata; secondly that RDF was an XML format rather than a data model, and only the RDF/XML serialisation being XML-based. RDF saw little take-up in this period, but there was significant work done in
The recommendation of 1999 was replaced in 2004 by a set of six specifications:[9] "The RDF Primer",[10] "RDF Concepts and Abstract",[11] "RDF/XML Syntax Specification (revised)",[12] "RDF Semantics",[13] "RDF Vocabulary Description Language 1.0",[14] and "The RDF Test Cases".[15]
This series was superseded in 2014 by the following six "RDF 1.1" documents: "RDF 1.1 Primer",[16] "RDF 1.1 Concepts and Abstract Syntax",[17] "RDF 1.1 XML Syntax",[18] "RDF 1.1 Semantics",[19] "RDF Schema 1.1",[20] and "RDF 1.1 Test Cases".[21]
RDF topics
Vocabulary
The vocabulary defined by the RDF specification is as follows:[22]
Classes
rdf
rdf:XMLLiteral
- the class of XML literal values
rdf:Property
- the class of properties
rdf:Statement
- the class of RDF statements
rdf:Alt
,rdf:Bag
,rdf:Seq
- containers of alternatives, unordered containers, and ordered containers (
rdfs:Container
is a super-class of the three) rdf:List
- the class of RDF Lists
rdf:nil
- an instance of
rdf:List
representing the empty list
rdfs
rdfs:Resource
- the class resource, everything
rdfs:Literal
- the class of literal values, e.g. strings and integers
rdfs:Class
- the class of classes
rdfs:Datatype
- the class of RDF datatypes
rdfs:Container
- the class of RDF containers
rdfs:ContainerMembershipProperty
- the class of container membership properties,
rdf:_1
,rdf:_2
, ..., all of which are sub-properties ofrdfs:member
Properties
rdf
rdf:type
- an instance of
rdf:Property
used to state that a resource is an instance of a class rdf:first
- the first item in the subject RDF list
rdf:rest
- the rest of the subject RDF list after
rdf:first
rdf:value
- idiomatic property used for structured values
rdf:subject
- the subject of the RDF statement
rdf:predicate
- the predicate of the RDF statement
rdf:object
- the object of the RDF statement
rdf:Statement
, rdf:subject
, rdf:predicate
, rdf:object
are used for reification (see below).
rdfs
rdfs:subClassOf
- the subject is a subclass of a class
rdfs:subPropertyOf
- the subject is a subproperty of a property
rdfs:domain
- a domain of the subject property
rdfs:range
- a range of the subject property
rdfs:label
- a human-readable name for the subject
rdfs:comment
- a description of the subject resource
rdfs:member
- a member of the subject resource
rdfs:seeAlso
- further information about the subject resource
rdfs:isDefinedBy
- the definition of the subject resource
This vocabulary is used as a foundation for RDF Schema, where it is extended.
Serialization formats
Filename extension |
.ttl |
---|---|
Internet media type |
text/turtle[23] |
Developed by | World Wide Web Consortium |
Standard | RDF 1.1 Turtle: Terse RDF Triple Language January 9, 2014 |
Open format? | Yes |
Filename extension |
.trig |
---|---|
Internet media type |
application/trig[24] |
Developed by | World Wide Web Consortium |
Standard | RDF 1.1 TriG: RDF Dataset Language February 25, 2014 |
Open format? | Yes |
Filename extension |
.rdf |
---|---|
Internet media type |
application/rdf+xml[25] |
Developed by | World Wide Web Consortium |
Standard | Concepts and Abstract Syntax February 10, 2004 |
Open format? | Yes |
Several common serialization formats are in use, including:
- Turtle,[26] a compact, human-friendly format.
- TriG,[27] an extension of Turtle to datasets.
- N-Triples,[28] a very simple, easy-to-parse, line-based format that is not as compact as Turtle.
- a superset of N-Triples, for serializing multiple RDF graphs.
- JSON-LD,[31] a JSON-based serialization.
- N3 or Notation3, a non-standard serialization that is very similar to Turtle, but has some additional features, such as the ability to define inference rules.
- RDF/XML,[32] an XML-based syntax that was the first standard format for serializing RDF.
- RDF/JSON,[33] an alternative syntax for expressing RDF triples using a simple JSON notation.
RDF/XML is sometimes misleadingly called simply RDF because it was introduced among the other W3C specifications defining RDF and it was historically the first W3C standard RDF serialization format. However, it is important to distinguish the RDF/XML format from the abstract RDF model itself. Although the RDF/XML format is still in use, other RDF serializations are now preferred by many RDF users, both because they are more human-friendly,[34] and because some RDF graphs are not representable in RDF/XML due to restrictions on the syntax of XML QNames.
With a little effort, virtually any arbitrary XML may also be interpreted as RDF using GRDDL (pronounced 'griddle'), Gleaning Resource Descriptions from Dialects of Languages.
RDF triples may be stored in a type of database called a triplestore.
Resource identification
The subject of an RDF statement is either a
In Semantic Web applications, and in relatively popular applications of RDF like
Therefore, producers and consumers of RDF statements must agree on the semantics of resource identifiers. Such agreement is not inherent to RDF itself, although there are some controlled vocabularies in common use, such as Dublin Core Metadata, which is partially mapped to a URI space for use in RDF. The intent of publishing RDF-based ontologies on the Web is often to establish, or circumscribe, the intended meanings of the resource identifiers used to express data in RDF. For example, the URI:
http://www.w3.org/TR/2004/REC-owl-guide-20040210/wine#Merlot
is intended by its owners to refer to the class of all Merlot red wines by vintner (i.e., instances of the above URI each represent the class of all wine produced by a single vintner), a definition which is expressed by the OWL ontology — itself an RDF document — in which it occurs. Without careful analysis of the definition, one might erroneously conclude that an instance of the above URI was something physical, instead of a type of wine.
Note that this is not a 'bare' resource identifier, but is rather a
Statement reification and context
The body of knowledge modeled by a collection of statements may be subjected to reification, in which each statement (that is each triple subject-predicate-object altogether) is assigned a URI and treated as a resource about which additional statements can be made, as in "Jane says that John is the author of document X". Reification is sometimes important in order to deduce a level of confidence or degree of usefulness for each statement.
In a reified RDF database, each original statement, being a resource, itself, most likely has at least three additional statements made about it: one to assert that its subject is some resource, one to assert that its predicate is some resource, and one to assert that its object is some resource or literal. More statements about the original statement may also exist, depending on the application's needs.
Borrowing from concepts available in
Implementation of scopes does not necessarily require fully reified statements. Some implementations allow a single scope identifier to be associated with a statement that has not been assigned a URI, itself.[38][39] Likewise named graphs in which a set of triples is named by a URI can represent context without the need to reify the triples.[40]
Query and inference languages
The predominant query language for RDF graphs is
The following is an example of a SPARQL query to show country capitals in Africa, using a fictional ontology:
PREFIX ex: <http://example.com/exampleOntology#>
SELECT ?capital ?country
WHERE {
?x ex:cityname ?capital ;
ex:isCapitalOf ?y .
?y ex:countryname ?country ;
ex:isInContinent ex:Africa .
}
Other non-standard ways to query RDF graphs include:
- RDQL, precursor to SPARQL, SQL-like
- Versa, compact syntax (non–SQL-like), solely implemented in 4Suite (Python).
- RQL, one of the first declarative languages for uniformly querying RDF schemas and resource descriptions, implemented in RDFSuite.[41]
- Sesame
- XUL has a template element in which to declare rules for matching data in RDF. XUL uses RDF extensively for data binding.
SHACL Advanced Features specification [42] (W3C Working Group Note), the most recent version of which is maintained by the SHACL Community Group defines support for SHACL Rules, used for data transformations, inferences and mappings of RDF based on SHACL shapes.
Validation and description
The predominant language for describing and validating RDF graphs is SHACL (Shapes Constraint Language).[43] SHACL specification is divided in two parts: SHACL Core and SHACL-SPARQL. SHACL Core consists of a list of built-in constraints such as cardinality, range of values and many others. SHACL-SPARQL describes SPARQL-based constraints and an extension mechanism to declare new constraint components.
Other non-standard ways to describe and validate RDF graphs include:
- SPARQL Inferencing Notation (SPIN) [44] was based on SPARQL queries. It has been effectively deprecated in favor of SHACL.[45]
- ShEx (Shape Expressions) [46] is a concise language for RDF validation and description.
Examples
Example 1: Description of a person named Eric Miller
The following example is taken from the W3C website[47] describing a resource with statements "there is a Person identified by http://www.w3.org/People/EM/contact#me, whose name is Eric Miller, whose email address is e.miller123(at)example (changed for security purposes), and whose title is Dr."
The resource "http://www.w3.org/People/EM/contact#me" is the subject.
The objects are:
- "Eric Miller" (with a predicate "whose name is"),
- mailto:e.miller123(at)example (with a predicate "whose email address is"), and
- "Dr." (with a predicate "whose title is").
The subject is a URI.
The predicates also have URIs. For example, the URI for each predicate:
- "whose name is" is http://www.w3.org/2000/10/swap/pim/contact#fullName,
- "whose email address is" is http://www.w3.org/2000/10/swap/pim/contact#mailbox,
- "whose title is" is http://www.w3.org/2000/10/swap/pim/contact#personalTitle.
In addition, the subject has a type (with URI http://www.w3.org/1999/02/22-rdf-syntax-ns#type), which is person (with URI http://www.w3.org/2000/10/swap/pim/contact#Person).
Therefore, the following "subject, predicate, object" RDF triples can be expressed:
- http://www.w3.org/People/EM/contact#me, http://www.w3.org/2000/10/swap/pim/contact#fullName, "Eric Miller"
- http://www.w3.org/People/EM/contact#me, http://www.w3.org/2000/10/swap/pim/contact#mailbox, mailto:e.miller123(at)example
- http://www.w3.org/People/EM/contact#me, http://www.w3.org/2000/10/swap/pim/contact#personalTitle, "Dr."
- http://www.w3.org/People/EM/contact#me, http://www.w3.org/1999/02/22-rdf-syntax-ns#type, http://www.w3.org/2000/10/swap/pim/contact#Person
In standard N-Triples format, this RDF can be written as:
<http://www.w3.org/People/EM/contact#me> <http://www.w3.org/2000/10/swap/pim/contact#fullName> "Eric Miller" .
<http://www.w3.org/People/EM/contact#me> <http://www.w3.org/2000/10/swap/pim/contact#mailbox> <mailto:e.miller123(at)example> .
<http://www.w3.org/People/EM/contact#me> <http://www.w3.org/2000/10/swap/pim/contact#personalTitle> "Dr." .
<http://www.w3.org/People/EM/contact#me> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/2000/10/swap/pim/contact#Person> .
Equivalently, it can be written in standard Turtle (syntax) format as:
@prefix eric: <http://www.w3.org/People/EM/contact#> .
@prefix contact: <http://www.w3.org/2000/10/swap/pim/contact#> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
eric:me contact:fullName "Eric Miller" .
eric:me contact:mailbox <mailto:e.miller123(at)example> .
eric:me contact:personalTitle "Dr." .
eric:me rdf:type contact:Person .
Or, it can be written in RDF/XML format as:
<?xml version="1.0" encoding="utf-8"?>
<rdf:RDF xmlns:contact="http://www.w3.org/2000/10/swap/pim/contact#" xmlns:eric="http://www.w3.org/People/EM/contact#" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
<rdf:Description rdf:about="http://www.w3.org/People/EM/contact#me">
<contact:fullName>Eric Miller</contact:fullName>
</rdf:Description>
<rdf:Description rdf:about="http://www.w3.org/People/EM/contact#me">
<contact:mailbox rdf:resource="mailto:e.miller123(at)example"/>
</rdf:Description>
<rdf:Description rdf:about="http://www.w3.org/People/EM/contact#me">
<contact:personalTitle>Dr.</contact:personalTitle>
</rdf:Description>
<rdf:Description rdf:about="http://www.w3.org/People/EM/contact#me">
<rdf:type rdf:resource="http://www.w3.org/2000/10/swap/pim/contact#Person"/>
</rdf:Description>
</rdf:RDF>
Example 2: The postal abbreviation for New York
Certain concepts in RDF are taken from logic and linguistics, where subject-predicate and subject-predicate-object structures have meanings similar to, yet distinct from, the uses of those terms in RDF. This example demonstrates:
In the English language statement 'New York has the postal abbreviation NY' , 'New York' would be the subject, 'has the postal abbreviation' the predicate and 'NY' the object.
Encoded as an RDF triple, the subject and predicate would have to be resources named by URIs. The object could be a resource or literal element. For example, in the N-Triples form of RDF, the statement might look like:
<urn:x-states:New%20York> <http://purl.org/dc/terms/alternative> "NY" .
In this example, "urn:x-states:New%20York" is the URI for a resource that denotes the US state New York, "http://purl.org/dc/terms/alternative" is the URI for a predicate (whose human-readable definition can be found here [48]), and "NY" is a literal string. Note that the URIs chosen here are not standard, and do not need to be, as long as their meaning is known to whatever is reading them.
Example 3: A Wikipedia article about Tony Benn
In a like manner, given that "https://en.wikipedia.org/wiki/Tony_Benn" identifies a particular resource (regardless of whether that URI could be traversed as a hyperlink, or whether the resource is actually the Wikipedia article about Tony Benn), to say that the title of this resource is "Tony Benn" and its publisher is "Wikipedia" would be two assertions that could be expressed as valid RDF statements. In the N-Triples form of RDF, these statements might look like the following:
<https://en.wikipedia.org/wiki/Tony_Benn> <http://purl.org/dc/elements/1.1/title> "Tony Benn" .
<https://en.wikipedia.org/wiki/Tony_Benn> <http://purl.org/dc/elements/1.1/publisher> "Wikipedia" .
To an English-speaking person, the same information could be represented simply as:
The title of this resource, which is published by Wikipedia, is 'Tony Benn'
However, RDF puts the information in a formal way that a machine can understand. The purpose of RDF is to provide an
Both versions of the statements above are wordy because one requirement for an RDF resource (as a subject or a predicate) is that it be unique. The subject resource must be unique in an attempt to pinpoint the exact resource being described. The predicate needs to be unique in order to reduce the chance that the idea of
The following example, written in Turtle, shows how such simple claims can be elaborated on, by combining multiple RDF vocabularies. Here, we note that the primary topic of the Wikipedia page is a "Person" whose name is "Tony Benn":
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix foaf: <http://xmlns.com/foaf/0.1/> .
@prefix dc: <http://purl.org/dc/elements/1.1/> .
<https://en.wikipedia.org/wiki/Tony_Benn>
dc:publisher "Wikipedia" ;
dc:title "Tony Benn" ;
foaf:primaryTopic [
a foaf:Person ;
foaf:name "Tony Benn"
] .
Applications
- DBpedia – Extracts facts from Wikipedia articles and publishes them as RDF data.
- YAGO – Similar to DBpedia extracts facts from Wikipedia articles and publishes them as RDF data.
- Wikidata – Collaboratively edited knowledge base hosted by the Wikimedia Foundation.
- Creative Commons – Uses RDF to embed license information in web pages and mp3 files.
- FOAF (Friend of a Friend) – designed to describe people, their interests and interconnections.
- Haystack client – Semantic web browser from MIT CS & AI lab.[49]
- Enterprise Architecture using RDF as the encoding.[50]
- Microsoft shipped a product, Connected Services Framework,[51] which provides RDF-based Profile Management capabilities.
- MusicBrainz – Publishes information about Music Albums.[52]
- NEPOMUK, an open-source software specification for a Social Semantic desktop uses RDF as a storage format for collected metadata. NEPOMUK is mostly known because of its integration into the KDE SC 4desktop environment.
- Cochrane is a global publisher of clinical study meta-analyses in evidence based healthcare. They use an ontology driven data architecture to semantically annotate their published reviews with RDF based structured data.[53]
- RDF Site Summary – one of several "weblogcontent.
- Simple Knowledge Organization System (SKOS) – a KR representation intended to support vocabulary/thesaurus applications
- SIOC (Semantically-Interlinked Online Communities) – designed to describe online communities and to create connections between Internet-based discussions from message boards, weblogs and mailing lists.[54]
- Smart-M3 – provides an infrastructure for using RDF and specifically uses the ontology agnostic nature of RDF to enable heterogeneous mashing-up of information[55]
- LV2 - a libre plugin format using Turtle to describe API/ABI capabilities and properties [56]
Some uses of RDF include research into social networking. It will also help people in business fields understand better their relationships with members of industries that could be of use for product placement.[57] It will also help scientists understand how people are connected to one another.
RDF is being used to gain a better understanding of road traffic patterns. This is because the information regarding traffic patterns is on different websites, and RDF is used to integrate information from different sources on the web. Before, the common methodology was using keyword searching, but this method is problematic because it does not consider synonyms. This is why ontologies are useful in this situation. But one of the issues that comes up when trying to efficiently study traffic is that to fully understand traffic, concepts related to people, streets, and roads must be well understood. Since these are human concepts, they require the addition of fuzzy logic. This is because values that are useful when describing roads, like slipperiness, are not precise concepts and cannot be measured. This would imply that the best solution would incorporate both fuzzy logic and ontology.[58]
See also
- Notations for RDF
- Similar concepts
- Entity–attribute–value model
- Graph theory – an RDF model is a labeled, directed multi-graph.
- Tag (metadata)
- SciCrunch
- Semantic network
- Other (unsorted)
- Semantic technology
- Business Intelligence 2.0 (BI 2.0)
- Data portability
- EU Open Data Portal
- RDF Schema
- Folksonomy
- LSID - Life Science Identifier
- Swoogle
- Universal Networking Language (UNL)
- VoID
References
Citations
- ^ "Resource Description Framework (RDF) Model and Syntax Specification". W3C. 5 January 1999. Archived from the original on Jul 14, 2023.
- ^ a b "World Wide Web Consortium Publishes Public Draft of Resource Description Framework". W3C. Cambridge, MA. 1997-10-03. Archived from the original on Jun 22, 2022.
- ^ a b Lash, Alex (1997-10-03). "W3C takes first step toward RDF spec". CNET News. Archived from the original on June 16, 2011. Retrieved 2015-11-28.
- ISBN 978-0-596-00881-9.
- ^ Lassila, Ora; Swick, Ralph R. (1997-10-02). "Resource Description Framework (RDF): Model and Syntax". W3C. Retrieved 2015-11-24.
- ^ Swick, Ralph (1997-12-11). "Resource Description Framework (RDF)". W3C. Archived from the original on February 14, 1998. Retrieved 2015-11-24.
- ^ Powers 2003, p. 2.
- ^ "Resource Description Framework (RDF) Model and Syntax Specification". 22 Feb 1999. Retrieved 5 May 2014.
- ^ Powers 2003, p. 3.
- ^ Manola, Frank; Miller, Eric (2004-02-10), RDF Primer, W3C, retrieved 2015-11-21
- ^ Klyne, Graham; Carroll, Jeremy J. (2004-02-10), Resource Description Framework (RDF): Concepts and Abstract Syntax, W3C, retrieved 2015-11-21
- ^ Beckett, Dave (2004-02-10), RDF/XML Syntax Specification (Revised), W3C, retrieved 2015-11-21
- ^ Hayes, Patrick (2014-02-10), RDF Semantics, retrieved 2015-11-21
- ^ Brickley, Dan; Guha, R.V. (2004-02-10), RDF Vocabulary Description Language 1.0: RDF Schema: W3C Recommendation 10 February 2004, W3C, retrieved 2015-11-21
- ^ Grant, Jan; Beckett, Dave (2004-02-10), RDF Test Cases, W3C, retrieved 2015-11-21
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- ^ Kellogg, Gregg; Lanthaler, Markus (2014-02-25), RDF 1.1 Test Cases, W3C, retrieved 2015-11-22
- W3C. 2004-02-10. Retrieved 2011-01-05.
- ^ "RDF 1.1 Turtle: Terse RDF Triple Language". W3C. 9 Jan 2014. Retrieved 2014-02-22.
- ^ "RDF 1.1 TriG: RDF Dataset Language". W3C. 25 Feb 2014. Retrieved 2022-12-21.
- ^ "application/rdf+xml Media Type Registration". Ietf Datatracker. IETF. September 2004. p. 2. Retrieved 2011-01-08.
- ^ "RDF 1.1 Turtle: Terse RDF Triple Language". W3C. 9 January 2014.
- ^ "RDF 1.1 TriG: RDF Dataset Language". W3C. 25 February 2014.
- W3C. 9 January 2014.
- ^ "N-Quads: Extending N-Triples with Context". 2012-06-25. Archived from the original on 2013-04-26.
- W3C. January 2014.
- ^ "JSON-LD 1.0: A JSON-based Serialization for Linked Data". W3C.
- W3C. 25 February 2014.
- W3C. 7 November 2013.
- ^ "Problems of the RDF syntax". Vuk Miličić.
- ^ "RDF 1.1 Concepts and Abstract Syntax". W3C. 25 February 2014. Archived from the original on Jan 14, 2024.
- ^ Klyne, Graham. "Contexts for Information Modelling in RDF". ninebynine.org.
- ^ Klyne, Graham (March 13, 2002). "RDF Contexts - provenance and partial knowledge". ninebynine.org. Archived from the original on Jul 29, 2023.
- ^ "The concept of 4Suite RDF scopes". Uche Ogbuji. Archived from the original on Dec 8, 2008.
- ^ "Redland Notes - Contexts". Redland RDF Libraries. 2004. Archived from the original on Jul 29, 2023.
- ^ "Named Graphs / Semantic Web Interest Group". W3C. Archived from the original on Oct 1, 2023.
- ^ "The RDF Query Language (RQL)". The ICS-FORTH RDFSuite. ICS-FORTH. Archived from the original on 2016-03-05. Retrieved 2011-03-29.
- ^ Knublauch, Holger; Allemang, Dean; Steyskal, Simon, eds. (8 June 2017). "SHACL Advanced Features". W3C. RDF Data Shapes Working Group (published 2017-06-08). Retrieved 2021-04-06.
- ^ [1] SHACL Specification
- ^ [2] SPIN website
- ^ [3] Comparison of SHACL with SPIN
- ^ [4] ShEx Specification
- ^ W3C. Retrieved 2009-03-13.
- ^ DCMI Metadata Term alternative. Dublincore.org. Retrieved on 2022-01-10.
- ^ "Haystack Group @ MIT CSAIL". groups.csail.mit.edu.
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- ^ "Connected Services Framework". microsoft.com.
- ^ "LinkedBrainz/RDF - MusicBrainz Wiki". wiki.musicbrainz.org.
- ^ "How knowledge graph technology is helping Cochrane respond to COVID-19". datalanguage.com.
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- ^ An RDF Approach for Discovering the Relevant Semantic Associations in a Social Network By Thushar A.K, and P. Santhi Thilagam
- ^ Traffic Information Retrieval Based on Fuzzy Ontology and RDF on the Semantic Web By Jun Zhai, Yi Yu, Yiduo Liang, and Jiatao Jiang (2008)
Sources
- Powers, Shelley (2003). Practical RDF. O'Reilly.
Further reading
- W3C's RDF at W3C: specifications, guides, and resources
- RDF Semantics: specification of semantics, and complete systems of inference rules for both RDF and RDFS