Topic Maps meet GeoSemantics

One of my main agendas here at the research center is to evaluate the usefulness of semantic technologies for geospatial applications. All this has to do a little bit with geographical maps, but much more prominently with time series of measurement data in large sensor networks.

As soon as you start to model such information with RDF or Topic Maps, you immediately realize that quite relevant information cannot be properly captured.

Units

One of the blatant omissions when dealing with values is that while RDF and TMs allow literals with types, the values themselves cannot have a unit.

Now when you measure something, or whenever you compute a new value from your data it always has a unit, and even if it is unit-less.

In RDF you could introduce more blank nodes to link the unit to, but this is just silly. Also the TM model does not really help you here.

So I simply decided to change the model. I had already modified my software in the direction of TMRM so that the type is an inherent part of the value (and not separate as dataType property of an occurrence). Now also values have a unit, undef being a default and uno being the empty unit.

Spatial Information

A little bit more effort it is to represent spatial information. That - as you might well know - can be manifested by a point in a coordinate system. But that of course gives you plenty of choices: UTM, GPS just to name the usual suspects.

Reverse geocoding is then the process to connect such a coordinate with an address, or simply a name such as Gramatneusiedl (which is a small and not massively attractive settlement in the neighborhood).

Together with a decent background ontology for geographical concepts and a proper infrastructure for geocoding and reverse geocoding you can capture a substantial part of the required information.

Of course, you want to train your software to always honor the transitivity of is-located-in associations.

Temporal Information

Much more thornier is the management of temporal information. Of course you could take the path and create a concept event and then attach dateTime information to instances of event, but there is much more to it (see OWL Time for the RDF frontier).

What we (that is Lara Spendier and /me) ended up doing, is to extend the Topic Maps model itself by forcing all associations to have a temporal extension. One can now say the station S123 was in Vienna from 21.04.2008 until 22.04.2008 and that is directly encoded into one association. On that we base all temporal concepts (before, after, etc).

Of course, the machinery has to be adapted to handle this piece of information now natively.

Time Series Information

What Lara also did was to create a language to express rather complex time patterns, such as in 2007 a particular sensor station was in Vienna every Mon, except in June and July, when it was a Wed.

That is needed for a number of things, among them to encode more or less regular measurements. These are normally organized in time series, but we have chosen to extend them (and actually every single measurement) by contextual, semantic information.

This will allow us to create transformers of time series not only on the numeric level, but also on the semantic level. The plan is to have a framework to gradually aggregate information and have a closed transformation chain from purely numeric time series data to more meaningful information.

So if your audio sensor delivers footsteps at the door, your Topic Map application will pop up and tell you

"Boss is coming, stop reading rho's blog".

Work supported by the Austrian Research Centers.

Posted In

Timing is everything

"... extend the Topic Maps model itself by forcing all associations to have a temporal extension."

+100

When I returned to making topic maps recently, it was instantly clear to me that whenever I made an association, I was often losing out if I had no way to say "when" the association was true.

sam hunting (not verified) | Thu, 07/31/2008 - 02:54

Then again

Why privilege time? Why not (say) money? (Serious question...)

sam hunting (not verified) | Thu, 07/31/2008 - 14:11

Re: Then again

Why privilege time? Why not (say) money? (Serious question...)

Money would be an equally good choice. Maybe not U.S. Dollars, for that matter. No.

But for a system which is about time sequences and geographic events, time seems to be more appropriate. And somehow I have the feeling that time will be around for some .... time. Cannot vouch for the greenback.

rho | Thu, 07/31/2008 - 21:11

Temporal Information

Could the temporal properties of topics and/or associations be encoded using some form of temporal scope or constraint?

Michael (not verified) | Fri, 08/15/2008 - 13:07

Re: Temporal Information

Could the temporal properties of topics and/or associations be encoded using some form of temporal scope or constraint?

That is what effectively have done, although we stayed away from the "scope" as TMDM defined it. Scope is a rather flaky concept, IMHO, so I left it unchanged and rather decided to introduce another, orthogonal constraint, time.

That way all my software can be backwards compatible for applications which are not time-aware.

rho | Fri, 08/15/2008 - 13:37

Time as an explicit dimension in models - great!

It is a very interesting problem! I typically also extend TMDM by attaching timestamp to constructs such as names, occurrences and associations. I also add date/time parameter to GET, CREATE, MODIFY, DELETE, FIND operations. Timestamps allow relatively quickly to create snapshots for any moment of time and do simple temporal "reasoning".

When I need to publish information as XTM, I use scope to represent time.

Dmitry (not verified) | Sun, 08/24/2008 - 16:32

Re: Time as an explicit dimension in models - great!

... extend TMDM by attaching timestamp ...

Just for the records: I am not using a timestamp, but a time interval. And it can be open left or right:

rho isa person since 1753 .

Read up, if you do not believe me.

rho | Sun, 08/24/2008 - 19:19

Topic Maps meet GeoNames

Hello

I Don't know if you are familiar with our GeoNames to Topic Maps conversion effort described in

http://www.wandora.org/wandora/wiki/index.php?title=Geonames_extractors

Unfortunately our experience on temporal Topic Map structures is limited to observation date of weather data.

However, I have been watching closely Semantic Computing Research Group (http://www.seco.tkk.fi/) where Tomi Kauppinen and Eero Hyvönen have written a paper on the issue. See

http://www.seco.tkk.fi/publications/2007/kauppinen_hyvonen_modeling_and_reasoning_about_changes_in_ontology_timeseries_2007.pdf

Kind Regards,
Aki Kivela
Wandora Team

akivela (not verified) | Tue, 01/13/2009 - 14:07

Re: Topic Maps meet GeoNames

... Wandora ... GeoNames to Topic Maps ....

I only read one announcement, but had no opportunity to check it out. Will have a look, thanks for letting me know.

... Tomi Kauppinen and Eero Hyvönen ...

I actually have seen a very similar paper (also from Finland, maybe the same authors?) when I studied temporal extensions to OWL at the beginning of 2008.

The problem we tried to solve is how time series (we use them in environmental monitoring systems) can be seamlessly integrated into a topic map. Conceptually, and also implementation-wise.

Needless to say, we have a lot of existing data which has to be virtualized into a map.

rho | Tue, 01/13/2009 - 14:46