Demo Code with Examples for educational purpose
- Linked Data
- Author: Tim Berners-Lee
- Date: 18.06.2009
Blank nodes are nodes in a graph that cannot be addressed by an URL. Thus irrelevant for plain statements, blank nodes can be used to build advanced structure e.g. linked lists.
Container types such as rdf:Bag, rdf:Seq and rdf:Alt are formally indifferent,
because a gaph does not impose any order to the edges of a node.
However, the type indicates to the human reader that there is a special meaning to the order of the items.
The class rdfs:ContainerMembershipProperty has as instances the properties rdf:_1, rdf:_2 ... .
Those properties are intended to assign members to a container.
Containers are open for extension.
A collection is a sub-graph that resembles a linked list.
The type rdf:List represents a node in the linked list with the properties rdf:first and rdf:rest.
The resource rdf:nil represents the terminal node in the linked list.
Collections are closed.
Reification allows modeling a statement explicitly, using a blank node of type rdf:Statement.
The properties rdf:subject, rdf:predicate and rdf:object may be used with a rdf:Statement.
In contrast to a simple triple, which is the implicit form of a statement, the explicit form e.g. is open for providing additional properties about the statement itself.
A taxonomy is an attempt to organize a (complex) system of seemingly unrelated concepts (e.g. terms) into classes, properties and relationships. Taxonomies are usually considered trees. While RDF is basically an abstract framework, both RDFS and OWL specify vocabulary to define taxonomies. OWL builds upon RDFS, yet needs to partially replace some of the RDFS-terms in order to introduce additional restrictions, required by its ontological features.
An ontology has a similar goal as a taxonomy, but allows the formalization of additional restrictions on classes, properties and relationships. Ontologies are usually considered graphs or hypergraphs. OWL specifies vocabulary to define ontologies.
There are 3 different levels of OWL:
| Level | Description |
|---|---|
| OWL Lite | A subset of OWL Full that is considered easy to implement |
| OWL DL | A subset of OWL Full that is determinalbe and equivalent to first order logic |
| OWL Full | Is not determinable, yet may be used as base for higher order logic |
Known meanings and conventions (i.e. semantic assumptions), defined within the specification of vocabularies auch as e.g. OWL DL, can be used to infer additional statements (known as an entailment regime) that may be considered valid under the presence of these assumptions.
- RDF 1.1 Primer
- RDF 1.1 Concepts
- RDF 1.1 Semantics
- RDF Schema 1.1
- OWL 2 Web Ontology Language Primer (Second Edition)
- OWL 2 Web Ontology Language Document Overview (Second Edition)
- SPARQL 1.1 Overview