18 Jul 2002 raph   » (Master)

A good blog

Phil Windley is the CIO for the State of Utah. His blog is well worth reading. We need more people like him in our government.


Antony Courtney points me to Twelf, a formal proof system from CMU. It looks interesting, although I haven't dug into it at all. For one, it's pretty difficult to figure out what license the software is released under.

Trustworthy metadata

I had a nice chat last night with Bram about the eigenvector metadata engine. He suggests that using medians rather than means as the way of combining ratings would be more attack resistant. I think he's right about that. With medians, if more than half of the confidence value comes from "good" nodes, then the result is guaranteed to be within the range of ratings published by "good" nodes. In particular, if "bad" nodes publish extreme high or extreme low ratings, then with a median they won't affect the outcome much, while with a mean they can.

Bram also reminded me of his Post from over a year ago. His design is actually fairly similar to the metadata engine as currently implemented in Advogato, but with some twists. For one, it may help with the scaling, because the confidence values go linearly down to 0 (at which point they need not be further propagated), while in the eigenvector formulation they tail off exponentially.

The analysis of his design is going to depend greatly on how the "distrust levels" are chosen. The subgraph of zero-distrust edges has no attack resistance among strongly connected components, so you probably want to avoid those. With distrust p, assertions travel over at most 1/p hops. If your distance to a "bad" node is greater than that, you only get recommendations from good nodes. That's not at all a bad property, although it's still a very good question how well it would work in practice.

It's really nice to have somebody to talk to who understands this stuff as deeply as Bram.

Expert witness

If you, or someone you know, is interested in being an expert witness in the area of database schema design, let me know. I was an expert witness for a halftone screening patent lawsuit a few years back, and I'm really glad I had the experience. I learned a lot about the way IP law works, and the pay can be pretty good too.


Alan's anxiety is much, much better now, and he seems overall happier.

Watching Max develop language ability continues to be a wonder. Typical sentences include "I take a picture at you, mommy" (holding a camera), "Put it on top your nose", and "I can't see his tail" (a cat in his favorite I Spy board book, with the tail indeed obscured). He's also starting to get into video games, including Galactic Patrol.

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