Ontology Alignment (is not the SameAs but is CloselyRelatedTo) Reconciling Worldviews

For the next three days, I’ll be reporting from the 8th International Semantic Web Conference (ISWC), taking place near Washington DC. A lot of what’s going on here is very technical, so rather than repeat everything I’m hearing, I’m going to talk about the broader themes that I see emerging. After this conference, I may try to tie them together into one comprehensive post.

This is my first theme. It’s about ontology alignment but is nevertheless very interesting. Yes, actually, it really is.

An ontology is basically a taxonomy of concepts and categories and the relationships between them – it’s sort of like a network but includes heritability (if I specify properties about some group, like “dogs can bark,” then it carries down to things within that group, so we know that Shih Tzus can bark). Ontologies are pretty key to the Semantic Web because expressing relationships between concepts is essentially defining those concepts – I could turn philosopher and argue that the meaning of something can only be found in the way it relates to other things. Or I could not, and just argue that defining things in terms of their relationships is a really useful way to do it, especially if the point is to make machines understand those things and be able to reason about them. That’s why a large percentage of the people here are obsessed with building ontologies about certain things (like jet engines).

But ontologies are personal. What if I think of “Shih Tzu” as a sub-category of “pets” but you think it belongs under “dinner proteins?” Or how about if a liberal defines a homosexual relationship as a type of family and a conservative thinks it belongs under sexual perversion? There’s no way the world would ever be able to agree on one definitive ontology. Nor should it. The way we categorize things, the way we cut up and connect up everything in the world is key to who we are, how we think, and what we do. I – an atheist and cognitive psychology nerd – would go so far as to say that the human soul exists in our subjective, idiosyncratic ways of linking up information. So to impose a single ontology on the whole world – no matter how well thought out and exhaustive it is – would be tantamount to mind control or soul stealing.

To their credit, most semantic technologists I’ve talked to think this way also. That’s why they’re encouraging ontologies to be fruitful and multiply and represent as many worldviews as there are ontology-builders (though ideally there would be more than 15. (I’m joking, I’m sure there are over 22 people who can build ontologies)). But having a bunch of rivaling ontologies out there that define and categorize things in unique ways doesn’t sound like much of an organized system of data, right? That’s true, and that’s why a lot of other people are involved in aligning ontologies – matching up the instances of some concept that shows up in different ontologies.

But…they’re still not doing it that well. That’s something Pat Hayes brought up during his keynote this morning. His topic was “blogic,” or, the new form of logic (formal logic) that’s required for the web. One of his problems with using traditional logic for the web is that people are mapping instances between different ontologies using the relationship “SameAs” – even though the fact that they come from different ontologies means they’re clearly not the same as each other. People are usually aware of that, but there’s still not much they can do because there’s no “SortOfSameAs” or “SameAsInThisOneParticularWay” relationships in traditional logic that they can use instead.

Ontology alignment is still a Big Problem and it’s acknowledged as such by much of the Semantic Web community. If anyone knows of good solutions in the works, I’d love to hear about them or add to this post with some comments.


7 thoughts on “Ontology Alignment (is not the SameAs but is CloselyRelatedTo) Reconciling Worldviews

  1. RJ says:

    There are not infinite ways of defining the same objects (or content). So they should be just a limited number of ontologies.
    As you have a limited number of dictionnaries.

    STOP this craziness saying that nothing is fully defined and everything is prone to free interpretation. Things ARE DEFINED, quite precisely, people have just to learn “words and grammar” correctly at school and everything will categorize correctly by itself, in libraries as well as on the web.
    Of course debates about how to categorize things are usefull and should maybe become a profession.
    Anyway, computer science and Internet is about treating information, either blogs, forum, images, video and so on. People should learn the ART OF CATEGORIZING things in the future in order to classify it right and avoid the mess. In that perspective, I think that regular education for the national language, the words and their meaning, some semantical understanding of the words themselves, correctly applying grammar, and most of all, practicing the language instead of just consumming information are the way to practice this Art correctly in the ‘real’ as well as the ‘virtual’ world.
    … So young people, understand and cultivate passion for your language, and everything will be ordered correctly !
    Up to now, everbody still call this big animal eating grass and producing milk a cow…
    So nothing new under the Sun, just doing our work as writer and producer of information.
    Regards 🙂 Raph

    • Lauren says:


      Dictionaries do NOT tell us how to understand our world. If someone writes that they will be “going into space”, can I just look up “space” in the dictionary, and then conclude that their claim is trivial because everyone is “in space” all the time.
      That points to the fact that word meaning is dependent on sentence context. These “meanings” therefore are far more numerous and flexible than the words themselves — that is part of why we need to identify ‘meanings’, not just words. Moreover, we want to reason about what is meant, so identifying real-world connections between meanings is important (e.g. to get to outer space, currently, rockets are required, etc.). This is why multiple models of meanings, and their worldly connections, are needed to explicitly interpret text.

      BUT, people do not always agree about those ‘worldly connections’ — e.g does “gay” refer to a type of relationship, or a sexual perversion? Which physical theory best identifies the nature of ‘space’? So there may be legitimate differences in how we tag our meanings one to the other.

      Moreover, for most words there simply AREN’T any essences to define their meaning, and thus no necessary and sufficient conditions we could specify for their ‘proper’ use (sure, “cow” is easy; try “game”, or “perfect” — what counts as a legitimate use of that term). So we have to recognize meaning is often built on fuzzy family resemblances, and the spectrum of literal-to-metaphorical has no clear breaking points.

      All of this is to say that you cannot POSSIBLY simply train our young people to order their worlds ‘correctly’ through the proper understanding of words. Nor can technology properly interpret our words without their also properly modeling the fuzzy, inconsistent, sometimes controversial ways we understand our world.

      ALL OF THAT sets the context in which sophisticated linguists and programmers go about modeling language, and world, to enable machine interpretation, web services, translation, etc.

      I just wish you were right, and all that was needed was a good dictionary. Unfortunately, it’s not that simple.
      – Lauren

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