Time, and TimeLine, Event
The parts of the Music Ontology related to the production process of a particular
piece of music (composition, performance, arrangement,...) as well as the parts dealing with time-related information are based
on three external ontologies. The Music Ontology provides RDFS wrappers for the main classes, properties and individuals
of these three ontologies we may use.
The first one is OWL-Time. We just use a few terms of it though: TemporalThing and
two of its sub-classes: Instant, and Interval.
However the kind of temporal information we may want to express goes a bit beyond OWL-Time, so we use an extension of it,
developped in the Centre for Digital Music, Queen Mary, University
of London: the TimeLine ontology. Indeed, we may want to express
instants and intervals on multiple "timelines" (a timeline being a coherent backbone for temporal things): the one backing
a particular audio file, the one behind an audio/video stream, or the physical one, backing a musical performance.
However, We use a really small subset of the TimeLine ontology (which is quite a complex DL one). Two classes of timelines
are defined: PhysicalTimeLine (an instance of it being universaltimeline, which is the one on which we may address "the 13th of october, 2006"),
and RelativeTimeLine (instances of this class may back audio signals, and we may address things such as "between 2 and 3 seconds" on them).
There is only one way of addressing temporal things per class of timeline. On a physical time line, a point is identified
by a xsd:dateTime -- through the beginsAtDateTime property, and a duration by a xsd:duration -- through the durationXSD property.
On a relative time line, a point P is identified by the duration of the interval [0,P], and this duration is identified by a xsd:duration
-- through the beginsAtDuration property. A duration is identified by durationXSD.
In order to express knowledge about the production process of a piece of music, we use the
Event ontology, also developped at the
Centre for Digital Music. Events, in it, are seen as a way
to arbitrary classify a space/time region. We might attach to them agents (active participants
to the event, like a performer, a sound engineer, ...), factors (passive things having a role in the
event, like a musical instrument, a musical score, ...), and products (things produced by the event, such as a sound,
a musical work, ...). A key feature of this ontology is also to allow "splitting" of events, through the
hasSubEvent transitive property. Using this, we may express: this musician was playing this instrument at this given time, for
example.
In the current version of the Music Ontology, the main sub-classes of Event are: Performance, Recording, Arrangement, Composition.
But, given its abstract definition, we will surely extend the things we may describe using this class: results of feature extraction,
beat tracking, segmentation of songs... Thus allowing Music Information
Retrieval results to be expressed within it!
The TimeLine ontology http://purl.org/NET/c4dm/timeline.owl#
The Event ontology http://purl.org/NET/c4dm/event.owl#
The Time ontology http://www.w3.org/TR/owl-time/