- From: Jim Hendler <hendler@cs.umd.edu>
- Date: Thu, 23 May 2002 09:21:44 -0400
- To: Jeff Heflin <heflin@cse.lehigh.edu>, Pat Hayes <phayes@ai.uwf.edu>
- Cc: www-rdf-logic@w3.org
All- have watched most of this discussion with one comment in my head "Phffft" - but guess that isn't enlightening enough, so I'll jump in both feet. Basically, I think real people (and I've got some real examples coming soon) are unlikely to use imports properly, and if you make imports automatic then the SW will probably never work w/real reasoners. Let me explain -- I've now taught sem web courses a couple of times, and will do again in the Fall. What I do is have my students write 20 facts about themselves they'd like to share w/the world, and a few weeks later they render them in DAML+OIL for a grade [1]. The students are exposed to the D+O reference manual and walkthru, but also to the ontology library and tools on the daml.org web page. (You can see the results of a recent class at [2], although the University did a renaming of backend servers without telling anyone so many of these are now broken links - another real-world sort of thing!) In almost every case (about 17 of 20 so far) the students have defined their ontologies by linking to existing ontologies and their instances as linking to multiple ontologies. As an example, one student wanted to say her dog was brown. She searched the ontology library and found that CYC had info about dogs -- she linked to the URI for http://.../cyc#dog and looked at what was there - decided it was okay. But it didn't have fur color, so in her ontology she defines fur color by including the cyc name space and then adding the property of furcolor with the string "brown" as its value (later in the term she went back and linked to a thing on colors Dan Connolly had created and added brown to his list). She also linked other facts about herself to other parts of CYC, to other ontologies (including several Jeff Heflin translated from SHOE), and to new classes she made up herself. [3,4] Now, on the inferencing end, a few things could happen -- i. we could insist this student has to understand all the info in CYC and agree to it (i.e. by using imports correctly) ii. we could automatically import all of cyc (and the others) iii. we can figure out some way to "import" only the cyc#dog facts or otherwise say when you use a URI from an ontology it only "commits" to some localized stuff (perhaps only the exact subgraph you point to) In the first case, the SW doesn't work because no way in heck is someone going to learn to commit to something like CYC by studying the whole thing and making sure it is consistent with her beliefs (imagine asking a naive user who wants to tell us about a dog that we need to go through a short little 40,000 step dialog to make sure she really understands what a dog is!) In the second case, the SW doesn't work because every inferencer will have to load the transitive closure of all the imported stuff - cyc alone is big enough to break most chainers, and this student also was linked to things in at least 5 other ontologies - and other students linked to hers. Inference will grind to a halt when the transitive closure of "imports" is the entire semantics of the web - we're already talking millions of assertions on daml marked up pages (and that's mostly ontologies, not the instances) In the third case, the user is happy, the algorithm designer is happy (with respect to scale), but the logician is unhappy -- this student is pointing at things which might be inconsistent!!! Oh, the horror! So my suggestion, learn to live with it!! If you cannot work in the real world of messy data and inconsistent semantics, then get the hell off the web. What can we do? Let's get some folks thinking about a modern view of inference and ontology where the whole (semantic) world is one huge interlinked ontology (as the whole web is one huge interlinked document) and figure out how to live with it - because if we can't, this whole enterprise is doomed from the start to be no more successful than current AI systems. -JH [1] http://www.cs.umd.edu/~hendler/CMSC498x/asst1.html [2] http://dormouse.cs.umd.edu:8080/wiki/assignment_1_submission_p.wiki [3] ontology: http://glue.umd.edu/~aloomis/498x/hw1-ont.n3 [4] instances: http://glue.umd.edu/~aloomis/498x/hw1.n3 -- Professor James Hendler hendler@cs.umd.edu Director, Semantic Web and Agent Technologies 301-405-2696 Maryland Information and Network Dynamics Lab. 301-405-6707 (Fax) AV Williams Building, Univ of Maryland College Park, MD 20742 http://www.cs.umd.edu/users/hendler
Received on Thursday, 23 May 2002 09:21:57 UTC