OWL-Time [[owl-time]] is an ontology for temporal entities, with a particular focus on the description of relations between time intervals. However, there are certain relations between more general temporal entities (in particular, time instants) that cannot be expressed using the 15 interval relations defined in OWL-Time. This note adds four new relations: time:equals, time:hasInside, time:disjoint and time:notDisjoint which complement the original relations and allow for description of more relationships between temporal entities.

The namespace for OWL-Time terms is http://www.w3.org/2006/time#

The suggested prefix for the OWL-Time namespace is time

The OWL-Time ontology is available here.

The OWL-Time ontology with these extensions is available here.

For OGC - This is a Public Draft of a document prepared by the Spatial Data on the Web Interest Group (SDWIG) — a joint W3C-OGC project (see charter). The document is prepared following W3C conventions. This document is not an OGC Standard. This document is distributed for review and comment. This document is subject to change without notice and may not be referred to as an OGC Standard. Recipients of this document are invited to submit, with their comments, notification of any relevant patent rights of which they are aware and to provide supporting documentation.

New properties are introduced in this extension to OWL-Time. The new elements concern relationships between temporal entities which cannot be easily expressed through combination of the predicates provided in OWL-Time using the axiomatization available in OWL2. The ontology document <owl:imports> the OWL-Time, and adds the new elements and axioms. IRIs denoting the new elements are placed in the OWL-Time namespace since it is expected that they could be added to the normative ontology in a future revision of OWL-Time.

Summary

Background

OWL-Time is an ontology for describing temporal entities and their relationships [[owl-time]]. The focus is particularly in relationships between time intervals, using the terminology originally defined by Allen [[?al-84]] [[?af-97]]. OWL-Time includes direct implementation of the following basic relationships that were identified by Allen:

A summary of the semantics of the intervals relationships is shown in .

Allen's primitive relations between intervals
Allen's relations between temporal intervals. Figure from [[owl-time]].

In principle, any relationship between temporal entities can be built up through logical combination of members of these primitive relations. However, in practice, there are limitations in the expressivity of the RDF implementation of OWL2 [[owl2-direct-semantics]][[owl2-rdf-based-semantics]], particularly around unions and complements of properties. Furthermore most of the relationships are only defined for proper-intervals - i.e. temporal entities of non-zero duration - which cannot be used for relationships involving time instants. These considerations mean that it is convenient to introduce a small set of additional relations explicitly, in order to support some applications more efficiently. Two were already included in OWL-Time:

  1. time:intervalIn is the the union of time:intervalDuring, time:intervalStarts,and time:intervalFinishes;
  2. time:intervalDisjoint is the the union of time:intervalBefore, and time:intervalAfter

Note that in OWL2 the union of properties can only be approximated through a set of sub-property axioms, which link the members up to the union, but does not exclude the possibility of other sub-properties being added to the union.

New temporal relations

This note defines a further four relations, all scoped to general temporal entities (i.e. not restricted to either intervals or instants):

  1. time:disjoint is the union of time:before, time:after, and time:intervalDisjoint;
  2. time:equals is the super-property of time:intervalEquals, but is not restricted to relations between proper intervals;
  3. time:hasInside is the union of time:inside, time:intervalContains, time:intervalStartedBy,and time:intervalFinishedBy;
  4. time:notDisjoint is the union of time:equals, time:hasInside, time:intervalIn, time:intervalMeets, time:intervalMetBy, time:intervalOverlaps, time:intervalOverlappedBy, which is the complement of time:disjoint

A graph showing the full set of 22 relations between temporal entitites is provided in .

Graph of all relations between temporal entities
All relations between temporal entities, shown as a graph with sub-property, inverse, and disjoint relationships

Notation and namespaces

Classes and properties from the are denoted in this specification using Compact URIs [[?curie]].

The namespace for all classes and properties in OWL-Time and this extension is http://www.w3.org/2006/time#.

The table below indicates the full list of namespaces and prefixes used in this document.

Prefix Namespace
ex http://example.org/ssn/
owl http://www.w3.org/2002/07/owl#
rdf http://www.w3.org/1999/02/22-rdf-syntax-ns#
rdfs http://www.w3.org/2000/01/rdf-schema#
time http://www.w3.org/2006/time#

Where class descriptions include local restrictions on properties, these are described using the OWL 2 Manchester Syntax [[?owl2-manchester-syntax]].

Examples and other code fragments are serialized using RDF 1.1 Turtle notation [[?turtle]].

Vocabulary specification

Properties

disjoint time entity

Property: time:disjoint
IRI: http://www.w3.org/2006/time#disjoint
Definition: If a temporal entity T1 is disjoint with another temporal entity T2, then the beginning of T1 is after the end of T2, or the end of T1 is before the beginning of T2, i.e. the two entities do not overlap or coincide in any way, but their ordering relationship is not known.
Instance of: owl:ObjectProperty
Sub-property of:
Domain: time:TemporalEntity
Range: time:TemporalEntity
Additional axioms: time:disjoint owl:propertyDisjointWith time:notDisjoint .
time:before rdfs:subPropertyOf time:disjoint .
time:after rdfs:subPropertyOf time:disjoint .
time:intervalDisjoint rdfs:subPropertyOf time:disjoint .

equal time entity

Property: time:equals
IRI: http://www.w3.org/2006/time#equals
Definition: If a temporal entity T1 equals another temporal entity T2, then the beginning of T1 is coincident with the beginning of T2, and the end of T1 is coincident with the end of T2, and the beginning of T1 may be coincident with the end of T1.
Instance of: owl:ObjectProperty
Sub-property of: time:notDisjoint
Domain: time:TemporalEntity
Range: time:TemporalEntity
Additional axioms: time:intervalEquals rdfs:subPropertyOf time:equals .

has time entity inside

Property: time:hasInside
IRI: http://www.w3.org/2006/time#hasInside
Definition: If a temporal entity T1 hasInside it another temporal entity T2, then the beginning of T1 is coincident with or before the beginning of T2, and the end of T1 is concident with or after the end of T2, except that end of T1 may not be coincident with the end of T2 if the beginning of T1 is coincident with the beginning of T2.
Instance of: owl:ObjectProperty
Sub-property of: time:notDisjoint
Domain: time:TemporalEntity
Range: time:TemporalEntity
Additional axioms: time:hasInside owl:propertyDisjointWith time:equals .
time:inside rdfs:subPropertyOf time:hasInside .
time:intervalStartedBy rdfs:subPropertyOf time:hasInside .
time:intervalContains rdfs:subPropertyOf time:hasInside .
time:intervalFinishedBy rdfs:subPropertyOf time:hasInside .

not disjoint time entity

Property: time:notDisjoint
IRI: http://www.w3.org/2006/time#notDisjoint
Definition: If a temporal entity T1 is notDisjoint with another temporal entity T2, then the the two entities overlap or coincide in some way, but their ordering relationship is not known. This relation is the complement of disjoint and is the union of equals, hasInside, in, meets, metBy, overlaps, overlappedBy.
Instance of: owl:ObjectProperty
Domain: time:TemporalEntity
Range: time:TemporalEntity
Additional axioms: time:notDisjoint owl:propertyDisjointWith time:disjoint .
time:equals rdfs:subPropertyOf time:notDisjoint .
time:hasInside rdfs:subPropertyOf time:notDisjoint .
time:intervalIn rdfs:subPropertyOf time:notDisjoint .
time:intervalMeets rdfs:subPropertyOf time:notDisjoint .
time:intervalMetBy rdfs:subPropertyOf time:notDisjoint .
time:intervalOverlaps rdfs:subPropertyOf time:notDisjoint .
time:intervalOverlappedBy rdfs:subPropertyOf time:notDisjoint .

Examples

Jack's wedding coincides with Abby's birthday in 2020.

You can't sleep and eat at the same time, but you could take a nap in the morning or afternoon.

A quiz will occur at some point during the class - it could be at the beginning, middle or end.

IANA Considerations

The link relation types below are proposed to be registered by IANA per Section 6.2.1 of [[RFC8288]]:


Acknowledgements

The editors would like to thank the Elf Pavlik for triggering the creation of this document.