Geospatial Semantic Web Blog

The W3C Geospatial Incubator Group recently published two reports on geospatial vocabularies and ontologies. The announcement came through the W3C Semantic Web News:

The final reports of the W3C Geospatial Incubator Group has just been published: Geospatial Vocabulary and Geospatial Ontologies. The first document also includes a reference to a GeoOWL ontology that relies on other, existing vocabularies (like GeoRSS or GML). The second document gives an overview of some other, existing ontologies in the area.

These two documents provide a good overview of existing vocabularies and ontologies. Use cases of geospatial ontologies are described in the Geospatial Vocabulary document. Based on my reading, the group has reached an agreement on a model for representing geometry objects (points, lines, polygons, etc.) but not yet on a model for expressing geospatial relationships (within, touches, overlaps, etc.).

GeoRSS seems to play an influential role in the described model. This is a good sign. To application developers, ontology construction is a means to an end. RSS and GeoRSS extensions enabled the creation of many useful applications. Building on these standards will encourage a broader community to embrace a Geospatial Wemantic Web.

OpenSearch is a collection of specifications that describe how search results can be shared between search engines and meta-search engines. A recent discussion thread on the GeoRSS mailing list brought about a debate over whether OpenSearch’s Geo extension is better than OGC’s Catalogue Service and vice verse.

OpenSearch was founded by A9 Inc., a subsidiary of Amazon.com. It’s a widely adopted specification on the Web today. Popular web search engines implement OpenSearch protocols and service descriptions. Modern browsers like IE7 and Mozilla Firefox have built-in support for OpenSearch extensions. For example, when you enter the string (e.g., “sea”) in the Firefox’s Search Engine toolbar, the toolbar will automatically display a list of possible matching keywords (e.g., “sears”, “search engines”, “sears.com” and “seattle times”). This feature is built-on the OpenSearch specification.

Some people see OpenSearch to be a direct competitor of other Web service description languages and specifications, including CSW, OWL-S and WSDL. I would agree with this thinking only if OpenSearch were designed to solve problems that others are trying to solve. In reality, this is not the case.

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Geonames released an ontology of its geospatial information schema in the Web Ontology Language OWL. This ontology directly maps to the DB schema that is used by Geonames data export.

In the rest of this post, I’ll describe key concepts in the Geonames ontology. It may be of interest to readers who want to learn and play with the Semantic Web Geonames.

In this ontology, among others, there are three key ontology classes: Feature, Class and Code. Feature class is a set of all geospatial instances in Geonames (a city, a country etc.). The ontology class Class is a set of all feature schemes defined in Geonames. Not to confuse this ontology concept with OWL Class, which is used to defined classes of ontological things, let’s call Geonames’s Class gn:Class. The class Code is a set of abbreviation feature codes in different feature schemes.

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The ability to represent time and temporal relations is an important aspect of the Semantic Web. W3C recently published a new working draft on Time Ontology in OWL. This work is an updated version of the OWL-Time ontology developed by Jerry Hobbs and Feng Pan.

Before the standardization of the OWL language, Jerry and Feng also worked on a version of the ontology in DAML. Their previous works on time ontologies can be found at Feng’s OWL-Time website.

In the RDF and OWL world, there are at least two different ways to represent time. One way is to use XSD datatypes (e.g., xsd:datetime), and the other is to use OWL-Time. Sometimes people ask me which approach is better for representing time in their applications.

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The term ontology should be no stranger to anyone who studies the Semantic Web. Even if it’s the first time that you’ve heard of this term, you can answer “what’s ontology?” by googling Wikipedia — “an ontology is a data model that represents a domain and is used to reason about the objects in that domain and the relations between them.”

On the Web, what counts as an ontology? This is a question that Tim Finin and Li Ding have explored in their paper “Untangling ontologies on the Semantic Web“.

In their research, they analyzed a collection of over 1.7 million Semantic Web documents (RDF documents) that were crawled by the Swoogle search engine. Based on the statistic data from their analysis, they inferred the characteristics of ontologies in the present Web and used this knowledge to answer the question: what counts as an ontology?

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Geospatial ontologies are formal representations of geographical concepts and relations. At the Networking Geospatial Information Technology, Jerry Hobbs of ISI gave an interesting presentation on understanding and developing geospatial ontologies.

His thesis is that in order to develop geospatial semantic web applications, we must first develop a core theory of geospatial and other spatial representation and reasoning. In particular, he discussed ontology development from a natural language perspective — e.g., how do we model queries such as “How long is chile?”, “How large is N. Korea?”, “How far is LA from Washington DC, as the crow flies?”

He also brought up a lot of interesting issues such as scales and half orders of magnitude.

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