TopicMaps

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Topic Identification

Topic identification, i.e. connecting your topics to the real world is a central TM paradigm. While the terminology is somewhat contrived (see some tutorials here and there) the principle actually is simple: either you have a subject which is a resource with a URL (so, an online document) or you have a subject with no appropriate URL (like my cat, although the page claims otherwise). In the latter case we can use URLs to indirectly indicate what subject we are talking about.

To demonstrate a topic which represents a resource on the Internet, we consider the Tokyo Airport (Narita) homepage. It is rather informative, a fact we would like to capture as occurrence value. For this purpose we create the topic, give it a name and everything else we know about the site:

Topic tNaritaHP = tMap.createTopic();
tNaritaHP.createTopicName( "Narita Homepage", null );
tNaritaHP.createOccurrence( "informative", null, null );

To link our topic with to web resource we first create a Locator using the URL and then set this locator as subject locator:

Locator locNarita = 
         tMap.createLocator ( "http://www.narita-airport.or.jp/airport_e/" ); 
tNaritaHP.addSubjectLocator( locNarita );

Note, that this is very different from using occurrence references. These are only attached URLs (or URIs, in general), saying something along the lines for more about that topic read here and there. A subject locator strongly connects a topic to a resource in such a way that when maps are merged, two topic having the same subject locator will be merged into one.

The situation is slightly different if we want to connect our topic tAirportTokyo with the actual airport. As that is no Internet resource, but has a homepage, we use that as subject indicator and the URL as subject identifier:

Topic tAirportTokyo = tMap.createTopic();
tAirportTokyo.createTopicName( "Narita", null );

tAirportTokyo.addSubjectIdentifier( locNarita );

Any number of subject identifiers can be added, in fact, the more you add, the more robust merging will be.