Introduction : The Semantic Web Foundation: RDF, URIs, and Ontologies Explained

Описание: This video provides an introduction to the core technologies of the Semantic Web, designed to help applications exchange data while preserving the original meaning.

Resource Description Framework (RDF) RDF is a formal language for describing structured information and is often viewed as the basic representation format for developing the Semantic Web. It was first officially specified by the W3C in 1999, initially focusing on representing metadata about Web resources.

Key concepts covered include:
• Graphs and Triples: RDF documents describe a directed graph, consisting of nodes linked by directed edges. This structure is preferred over tree structures (like XML) because RDF was designed to describe general relationships and is more suitable for integrating decentralized and distributed data found on the World Wide Web. RDF graphs are represented as a collection of triples: subject, predicate, and object.
• Serialization: RDF graphs can be serialized into textual formats for storage and processing, such as Turtle (Terse RDF Triple Language), formalized in 2014, and RDF/XML, the main XML-based serialization syntax.
URIs and Identification A major goal of RDF is to solve identifier ambiguity when composing or integrating distributed data. URIs (Uniform Resource Identifiers) are used to uniquely identify resources, labeling both the nodes (subjects/objects) and the edges (predicates) in an RDF graph. URIs solve the problems of the same resource having different identifiers, and the same identifier referring to different resources.
• URIs are broader than URLs and are used for identification, even for objects (like people or books) that are not web-accessible.
• Data values, such as numbers or strings, are represented using literals. Literals can have explicit datatypes, often using XML Schema datatypes for broader compatibility, which influences how values are interpreted (e.g., "42" as a string vs. as a number).
Ontologies (RDFS and OWL) For defining background information and the semantic characterization of vocabulary terms, RDF Schema (RDFS) and the Web Ontology Language (OWL) are introduced.
• RDFS provides generic language constructs to define user-specific vocabularies, enabling software that supports RDFS to automatically interpret these vocabularies semantically. RDFS allows for the definition of classes, subclasses using rdfs:subClassOf, and properties, including property hierarchies (subproperties) and restrictions (domain and range).
• OWL is a W3C recommended standard for ontology modelling. It describes concepts unambiguously using set theory and logic, allowing complex concepts to be built from simpler ones. OWL offers three species (Lite, DL, Full) and its ontologies consist of individuals, properties, and classes. OWL classes can be defined using various restrictions, including quantifier restrictions (existential/universal) and cardinality restrictions.