Semantic Web Glossary

When I was learning all these terms one by one, I really would have benefited from a central and comprehensive place where I could have gone to look up terms. I put the glossary together, hoping to make it as comprehensive as possible and will be adding to it and improving it moving forward. I hope it helps people.

ABox - Used to describe statements in ontologies; an assertion; a fact that is associated with a terminological vocabulary within a knowledge base; A-Box statements are sometimes associated with instances of T-Box classes.

Blank Node – A resource, or node in an RDF graph, which is not identified by a URI; can be used as subject or object in an RDF triple (RDF statement).

Closed World Assumption – Presumption stating that the statements we have are the only statements that need be considered. If something is not referenced in our data set, we assume it does not exist.

DAML+OIL - A successor language to DAML and OIL that combines features of both; it is now “outdated” because it was superseded by Web Ontology Language (OWL).

DataTypeProperty - Relationship between instance of classes and literal values such as string, number, and date.

Description Logics (DL) – A family of knowledge representation languages which can be used to represent the concept definitions of an application domain in a structured and formally well-understood way. See also OWL Lite, OWL DL and OWL Full.

DL – See Description Logics.

Entailment (logical implication) – In Semantic Web, one of the key inference ideas; a relationship between two pieces of knowledge where the truth of the first piece of knowledge requires the truth of the other.

Ground RDF Graph - RDF graph with no blank nodes.

HTML – Hypertext Markup Language; language used to encode formatting, links and other features on Web pages.

Individuals – Instances of classes; properties may be used to relate individuals to each other.

Inference – Process of deriving a conclusion from premises; in semantic web it is performed by a reasoner software and is used to extract explicit knowledge from implicit logic and add it to the original data set.

Literal – Used to identify values such as numbers and dates by means of a lexical representation. A literal may be the object of an RDF statement, but not the subject or the predicate.

Model Theory – specifies the semantics of a formal language; assumes that the language refers to a ‘world’, and describes the minimal conditions that a world must satisfy in order to assign an appropriate meaning for every expression in the language.

N-Triple – Also N-Triple format; a line-based, plain text format for encoding an RDF graph that is intended for better human readability of the RDF document.

Natural Language Processing (NLP) - Field of computer science concerned with the interactions between computers and human (natural) languages. Natural language generation systems convert information from computer databases into readable human language while natural language understanding systems convert samples of human language into more formal representations that are easier for computer programs to manipulate.

Object – In an RDF triple, the subject is the third of the three [Subject Predicate Object]; it is either a resource (blank node is a resource also) or a literal.

ObjectTypeProperty - Relation between instances of two classes.

Ontology – A data set describing things and their existence in the world.

OWL - see Web Ontology Language.

Open World Assumption – presumption stating that everything we don’t know is undefined.

OWL Lite - An owl class (owl:class) is defined as subclass of rdfs class (rdfs:class); not all classes of RDF document can be an instances or subclasses of an owl class (owl:class); as a result, a valid rdf document cannot be considered as a valid OWL Lite or DL document. It is different from OWL DL in lower level language details and constraints.

OWL DL – An owl class (owl:class) is defined as subclass of rdfs class (rdfs:class); not all classes of RDF document can be an instances or subclasses of an owl class (owl:class); as a result, a valid rdf document cannot be considered as a valid OWL Lite or DL document. It is different from OWL Lite in lower level language details and constraints.

OWL Full - A class (owl:class) is defined as equivalent to an rdfs class (rdfs:class). This enables any valid rdf document to be considered as a valid OWL full document. Similarly, In OWL full, owl:ObjectTypeProperty is considered equivalent to rdf property. DataTypeProperty, which is a subclass of rdf:property, is also a subclass of owl:ObjectTypeProperty. This means that any property in OWL that is defined as datatype can also be interpreted as objectype property. This allows much of the expressiveness in OWL full.

Pellet - Open-source Java OWL DL reasoner.

Predicate – In an RDF triple, the subject is the second of the three [Subject Predicate Object]; it is always a property.

Property – A binary relation that states relationships between classes/individuals or from an class/individual to data value. Property can be further distinguished as ObjectTypeProperty or DataTypeProperty.

RDF – Resource Description Framework. An XML-based language for describing online resources.

RDF Graph - Set of RDF triples.

RDF Subgraph – A subset of the triples in the graph.

RDF Triple – see Triple.

RDFS – Resource Description Framework Schema.

Reasoner – Software able to infer logical consequences from a set of asserted facts or axioms which creates a richer knowledge base.

Resource – Anything that has a valid unique resource identifier (URI).

Semantic Web – Extension of the World Wide Web in which the semantics of information and services on the web is defined, making it possible for the web to understand and satisfy the requests of people and machines to use the web content; also known as web3.0

SHER - Highly scalable Pellet-backed OWL DL reasoner.

SPARQL – SPARQL Protocol and RDF Query Language (pronounced “sparkle”) is an RDF query language much like SQL is a relational DB query language.

Statement - an assertion about the world; in semantic web it is usually a part of a vocabulary or an ontology; it usually consists of a “triple” structure of [subject predicate object].

Subject - In an RDF triple, the subject is the first of the three [Subject Predicate Object]; Object – In an RDF triple, the subject is the third of the three [Subject Predicate Object]; it is always a resource (blank node is a resource also).

T-Box – used to describe statements in ontologies; T-Box statements describe a system in terms of controlled vocabularies, for example, a set of classes and properties. T-box statements are sometimes associated with object-oriented classes.

(Sir) Timothy John Berners-Lee – an English computer scientist and MIT professor credited with inventing the World Wide Web and semantic web.

Triple – A basic RDF statement resembling the English-Language construct of [subject predicate object] that is made up of [Resource property Resource] or [Resource property Literal].

Typed Literal - A string combined with a datatype URI in order to express information about the datatype of the literal i.e. weight, length, height.

URL (Uniform Resource Locator) – The familiar constructs such as http://www.semanticalley.com/ that are used in hyperlinks.

URI (Universal Resource Identifier) – URLs are the most familiar type of URI; a URI defines or specifies an entity, without necessarily by naming its location on the Web.

Vocabulary (of a graph) – Set of classes and properties which occur as the subject, predicate or object of any triple in an RDF graph.

W3C – World Wide Web Consortium.

Web 1.0 – Static, minimally-interactive pages containing photos and text documents.

Web 2.0 – Use and design of the web with strong emphasis on reusability and sharing, with information traveling fast and being easy to get to. Widgets and tagging are two examples of features in Web2.0

Web 3.0 - see “semantic web.”

Web Ontology Language (OWL) – Family of knowledge representation languages for authoring ontologies, consisting of three languages: OWL Lite, OWL DL, and OWL Full.

XML – eXtensible Markup Language; general-purpose specification for creating custom markup languages.