Time Ontology Extended for Non-Gregorian Calendar Applications

Tracking #: 870-2080

Simon Cox

Responsible editor: 
Mark Gahegan

Submission type: 
Ontology Description
We extend OWL-Time to support the encoding of temporal position in a range of reference systems, in addi-tion to the Gregorian calendar and conventional clock. Two alternative implementations are provided: as a pure extension or OWL-Time, or as a replacement, both of which preserve the same representation for the cases origi-nally supported by OWL-Time. The combination of the generalized temporal position encoding and the temporal interval topology from OWL-Time support a range of applications in a variety of cultural and technical settings. These are illustrated with examples involving non-Gregorian calendars, Unix-time, and geologic time using both chronometric and stratigraphic timescales.
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Solicited Reviews:
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Review #1
By Karl Grossner submitted on 15/Nov/2014
Minor Revision
Review Comment:

This article makes a nice contribution to the domain of temporal modeling and I gladly support its acceptance. I have a few comments explaining why, list some challenges that may be out of scope here, plus a couple of relatively minor suggestions. I think the paper stands on its own but I'd welcome thoughts on, or flagging of, those challenges.

By articulating the classes of temporal reference systems (TRSes) from ISO 19108, the Time-plus and Time-new extensions to OWL-Time offer a promising start to helping that ontology better support historical and geo-historical knowledge representation. The author properly constrains the paper by making a "stub" for others' formal representations of non-Gregorian calendars and so forth, but demonstrates nicely how named historical periods can be defined, and start points for any calendar also using a form of year/month/day structure (Hebrew, Buddhist, e.g.) can be defined.

I don't think these extensions address a couple of cases I'm especially interested in, but I allow that those needs might be met at a higher, application layer (or by another extension). That is: 1) how do we describe an instant in a multi-year span? For example, how can we express born in (1901 or 1902)? If only "time:year '1901'" is given for a dateTimeDescription, and unitType is unitDay, we can I suppose rely on an as yet unavailable reasoner to know it's some time during that year and not throughout. But how can this be done for multi-year intervals?; and 2) historical data so often arrive as "about" or "circa," a case that might be handled by adding hasLatestBeginning and hasEarliestEnd to hasBeginning and hasEnd, forming a quad that can be used to construct a curve (or ignored if they're not given). This "interval bounded by either instants or intervals" pattern has been used well in Simile Timeline, and in analog fashion for a very long time.

The paper is cogent and highly readable, apart from a couple of minor points:
- Another sentence or two explaining the "complications [which] arise from the involvement of datatypes from XML Schema that are tied to the Gregorian calendar" would be helpful I think. It took some digging to get a grasp of those, which would have been aided by a little elaboration.
- not sure why both "time:intervalBefore geotime:Ordovician" and "time:intervalMeets geotime:Ordovician" appear in the example, aren't they distinct?

Given the nature of historical data, the answer to whether two individuals were spatial-temporal contemporaries is often 'possibly.' Modeling instants, intervals, and named periods such that we can compute probabilities to e.g. drive comparisons or rank search results is an unmet challenge. It could be argued that case and others like it are uncommon, and don't warrant attention in highly general standards. In any case, the extensions in this paper, by permitting Period definitions and topological relations between Periods, while remaining compatible with OWL-Time, constitute real progress. I plan to work with some of its constructs in my own development of the Topotime model and software.

Review #2
By Brandon Whitehead submitted on 08/Jan/2015
Review Comment:

This manuscript was submitted as 'Ontology Description' and should be reviewed along the following dimensions: (1) Quality and relevance of the described ontology (convincing evidence must be provided). (2) Illustration, clarity and readability of the describing paper, which shall convey to the reader the key aspects of the described ontology.

The author has developed an extension to the time ontology (OWL-Time) as described in the W3C working draft. The impetus behind the extension is the ability to encode temporal values and categories other than those described by the Gregorian calendar. The author mentions other temporal units and categorizations which are of particular value (i.e. GPS, UNIX time, geologic time scale, etc.) which are not yet able to utilise OWL-Time natively. The current version of OWL-Time inherits its values from the datatypes defined by the W3C recommended XML Schema, which are in turn inherited from the definitions delineated in ISO 8601.

The two proposed ontologies extending OWL-Time are Time-plus and Time-new.
Time-plus effectively clones the current representation but customises the property values to provide a generalized (or non-typed) domain and range which allows for the instantiation of any calendar one can conceive.

The Time-plus ontology also adds a mechanism to describe a temporal reference system (TRS), which is simply a placeholder for any concievable TRS to hook in to the structure. This stub can be beneficial when dealing with Unix time values or values from a geologic time scale.

However, as the author states, removing the constraints on the datatypes means that value based reasoning will be negated in generic reasoners. This perhaps negates some of the utility of this particular ontology engineering effort.

The Time-new ontology restructures the class hierarchy of OWL-Time and the Time-plus ontology to create the aptly named new ontology meant to supplant the original - as well as any modifications.

The author then provides several examples illustrating the utility of the proposed ontologies via several encodings of an instant in time, an event (geologic time), and ordinal relationships (also using geologic time).

As an ontology description paper (short paper) it outlines the need for each ontology created and provides working examples of their utility. The author also illustrates how the ontologies relate to any encodings that may utilise the original OWL-Time datatypes.

Both proposed ontologies were successfully downloaded and viewed using the NeOn Toolkit and Protégé.

minor ponderings:
- the use of "some communities" on page 1, para 2 is redundant (the wording, not the content)
- prefix designations in text vs in a footnote

Review #3
Anonymous submitted on 13/Jan/2015
Review Comment:

This paper describes an extension of the well-known OWL-Time ontology to support additional temporal reference systems beyond the Gregorian calendar and conventional clock. The paper presents two implementations: a pure extension of OWL-Time and a replacement of OWL-Time. The latter implementation yields a more natural class hierarchy.

(1) Quality and relevance

The presented ontologies are well-thought-out and clearly motivated. Existing descriptions of time values from the Gregorian Calendar encoded with OWL-Time do not need to be modified, and the new extensions are simple and general enough to encode all classifications of temporal reference systems defined in ISO 19108. In addition, the basic structures of OWL-Time related to Allen's temporal interval calculus are independent of the particular temporal reference system used and do not need to change. The need for a standard way to encode different types of temporal reference systems is clearly motivated in the Introduction with plenty of examples.

(2) Clarity and completeness of the descriptions

The paper is well-written and the ontologies are clearly described. The basic features of the ontologies are motivated and introduced one-by-one throughout the paper, which makes the ontology descriptions quite easy to understand.

The broad range of examples in Section 4 help to show how the OWL-Time extensions can easily be used to represent time values ranging from a person's birthday to the end of the age of dinosaurs.

I think the paper could be improved with a discussion of how the ontologies fit within the various profiles of OWL 2. That is, which features of the ontologies are not expressible in OWL 2 EL, RL or QL? This would give readers a better idea of how much reasoning can be done with off-the-shelf tools.


Apologies - the ontologies described in the paper are at
html, rdf, ttl versions available
(in the text the last "/" appears as a "-")