Re: [ontolog-forum] Time representation

[Pat Hayes <phayes@xxxxxxx>]

At 9:37 AM -0500 1/21/08, John F. Sowa wrote:

> Paola,
>
>  > what is the accepted syntax for pTim
>  > can pTim be a timestamp?  is there a prescribed
> format
>  > for time/date in ikl
>
> The dyadic relation PTim (point in time) is not an official
> part of either conceptual graphs or IKL.  It is part of an
> ontology for time, which I commonly use with CGs.  (And yes,
> I would be happy to send or point to the ontology, if I had
> it written down in a convenient form.  Right now, it is
> scattered in a very inconvenient form.)

There are a lot of ontologies for time, in various notations, all pretty similar except of course for the all-important details. I wrote a survey of some of the many options some time ago (all written in KIF), which is available here

http://www.ihmc.us/users/phayes/TimeCatalog.pdf

and since then a fairly 'standard' ontology was put together for the W3C OWL-based SWServices project by Jerry Hobbs and Feng Pan, originally written in a conventional FOL notation and then as far as possible transcribed into OWL.

http://www.w3.org/TR/owl-time/

There is a lot of commentary, advice, etc.., about this, see for example http://www.geospatialsemanticweb.com/2006/09/29/tips-on-using-the-w3c-owl-time-ontology

and it contains a lot of new stuff, eg a complete ontology of international time-zones and so on. It is probably the most thoroughly worked out 'practical' time ontology.

BTW, if you see a reference to DAML-Time, it was the early version of this, now obsoleted.

The XMLSchema datatype scheme has a fairly complex temporal naming system worked out for dates and times, but it gets rather tangled when it tries to merge months and days.

> As I use it, the first argument of PTim
> is some physical event
> or situation, and the second argument is some time specification.
> Since I assume that time "points" can never be observed
> or
> specified as true points, there is always
> an implicit granularity.

Pity you called them 'points', then, as they are in fact intervals :-) How do you handle endpoints of intervals: are they intervals also? One problem with this approach is that the Allen relationships change when you change granularity levels, which wrecks some reasoners.

> Therefore, the second argument could be
> any of the following,
> each of which has a default granularity determined by the least
> significant digit of the specification:
>
>     [Date: "21 January 2008"] -- granularity
> of 1 day
>
>     [Time: "21 January 2008, 14:03"] --
> granularity, 1 minute
>
>     [Time: "21 January 2008, 14:03:16.217"]
> -- granularity, 1 ms

Cute. The OWL-Time used a similar device, borrowed I believe from the CYC temporal ontology, in which each successive layer of granularity is treated as a 'selection' function on the previous level, so that 21 January 2008 has the structure 'the 21st day of( the first month of( the 2008th year of(The Christian Calender)))'. This makes both temporal and logical sense.

> As pure logics, CGs, CL, and IKL have no ontology or prescribed
> format for time, space, or anything else.  Any string
> enclosed
> in double quotes is interpreted as a name in those languages.
> Therefore, "21 January 2008, 14:03:16.217" would be the
> name
> of some entity of type Time.  The assumptions about
> granularity
> are not official parts of CGs or any of the other languages.
>
> But any project that used any of those languages would have to
> adopt some standard representation for times and dates, and
> the ontology would also have to include axioms that stated any
> default assumptions about granularity.

Do you have any granularity axioms? That is one of the hardest ontological problems, in my experience.

Pat

> John
>
>  
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