Introduction

Overview

GQLDB supports ontology features that bring semantic web capabilities to your graph database.

Key Concepts

• RDF: The Resource Description Framework — the W3C data model this builds on. Every fact is a triple (subject–predicate–object, e.g. ex:alice ex:knows ex:bob); subjects and predicates are IRIs, objects are IRIs or literals, and a set of triples forms a graph.
• IRI Identity: Classes, properties, and individuals are identified by globally unique IRIs, addressed in queries via the @prefix:LocalName shorthand.
• Prefixes: Local aliases for IRI namespaces, such as foaf: → http://xmlns.com/foaf/0.1/.
• Classes: Node types organized by SUBCLASS OF hierarchy, DISJOINT WITH exclusivity, EQUIVALENT TO membership etc..
• Object Properties: Edge types with DOMAIN / RANGE and OWL characteristics (SYMMETRIC, TRANSITIVE, FUNCTIONAL, INVERSE OF, etc.).
• Data Properties: XSD-typed node attributes (xsd:string, xsd:integer, etc.), optionally constrained by cardinality.
• Ontologies: Formal, explicit specification of a shared conceptualization containing classes, properties, and the axioms that constrain how they relate.

LPG vs Ontology Graph

Creating Ontology Graphs

Create a graph with ontology support:

GQL
CREATE GRAPH myOntology WITH ONTOLOGY

Loading Prefixes

A prefix is a short alias for a long IRI (Internationalized Resource Identifier). Ontology terms are identified by full IRIs, a prefix lets you write a short name instead.

For example, after loading foaf as an alias for http://xmlns.com/foaf/0.1/, the term <http://xmlns.com/foaf/0.1/Person> can be written as the ontology label @foaf:Person in GQL graph patterns.

Prefixes are loaded per-graph. After creating an ontology graph, you start with no prefixes loaded.

Standard Prefixes

Load all built-in standard prefixes:

GQL
LOAD ALL PREFIX

It registers the built-in standard set below in one step. These cover the common RDF, RDFS, OWL, and vocabulary namespaces:

Any prefix outside this set (e.g. a domain vocabulary like dbo) must be loaded explicitly with LOAD PREFIX.

Loading a Prefix

To load a prefix:

GQL
-- Load a vocabulary outside the standard set (prefix name + namespace IRI)
LOAD PREFIX ex FROM 'http://example.org/'
LOAD PREFIX dbo FROM 'http://dbpedia.org/ontology/'

-- FROM also accepts an IRI literal (angle-bracketed)
LOAD PREFIX dbo FROM <http://dbpedia.org/ontology/>

Bulk-Loading from an RDF Document

To bulk-load all prefixes declared in an RDF document at a URL or file path:

GQL
LOAD PREFIX ALL FROM 'http://xmlns.com/foaf/spec/index.rdf'
LOAD PREFIX ALL FROM <http://xmlns.com/foaf/spec/index.rdf>
LOAD PREFIX ALL FROM 'file:///srv/onto/foaf.ttl'

Aliases and IRI Identity

A few things follow from prefixes being local aliases:

• The prefix is just your local alias for the full IRI. LOAD PREFIX bigbird FROM 'http://xmlns.com/foaf/0.1/' works, and @bigbird:Person then means the same FOAF Person that @foaf:Person would. By convention, reuse the community-standard names (foaf, rdfs, schema, ex).
• Identity is by full IRI, not by short name. FOAF's Person (http://xmlns.com/foaf/0.1/Person) and Schema.org's Person (http://schema.org/Person) are distinct classes in the database even though both spell their local name Person; the prefix is what keeps them apart. A single node can be tagged as both without contradiction.

Viewing Prefixes

View loaded prefixes:

GQL
SHOW PREFIX

Dropping Prefixes

Drop a prefix:

GQL
DROP PREFIX foaf

After dropping a prefix, ontology labels that referenced it (@foaf:Person, etc.) no longer resolve at parse time and queries using the short form fail. Any nodes / edges already stored under the prefix's full IRIs remain in the graph (the database stores IRIs, not the short name); re-LOAD PREFIX foaf FROM '…' to address them by short form again.

RDF

Import external ontologies and RDF data into a graph and export it back out, and work with RDF data-model features (literals, blank nodes, named graphs, triple terms, etc.). See RDF Import & Export and Working with RDF.

Classes & Properties

Define the ontology's building blocks: classes and their object / data properties, with hierarchy, characteristics, and constraints. See Classes, Object Properties, and Data Properties.

Inspecting & Visualizing

Inspect loaded or defined ontologies, or project it as a queryable graph. See Inspecting & Visualizing Ontologies.