Kant in the information age

Uit het schetsboek van...

2006-01-30T08:58:00.000-08:00

My brother Barthel Brussee started his own blog Uit het schetsboek van.... He is an artist, so he has an interesting life and has the progress of his painting and sculptures to show. He is quite productive (one post a day).

I think I should put some of his work on the special new streetart recommendation website produced by students of the HKU (hoge school voor de kunsten)
ondergrond. Check it out at www.ondergrond.org

Uit het schetsboek van...

2006-01-30T08:56:00.000-08:00

My brother < href= "www.barthelbrussee.nl">Barthel Brussee started his own blog Uit het schetsboek van.... He is an artist, so he has an interesting life and has the progress of his painting and sculptures to show. He is quite productive (one post a day, he has more posts than I ever did), and he writes well (in Dutch) I think!

Hmm, I think I should put some of his work on the special new streetart recommendation website produced by students of the HKU (hoge school voor de kunsten)
ondergrond. Check it out at www.ondergrond.org

Anjo Anjewierden: What is a Topic?

2005-12-20T06:32:00.000-08:00

Because it is the holliday season, Anjo Anjewierden asks what is the topic ?. Now anybody who has ever attended a party (which are seasonally superabundant at the moment) and casually joins in a conversation, knows that it may take a while to actually find out. One reason is ofcourse that some conversations (especially at parties) serve no other purpose than giving the participants the idea that they belong to the same group, or, like the more flirtatious ones, that the participant(s) want to raise the level of intimacy. Thus, if you are an outsider to the group, you may come to the conclusion people are discussing work, when what they really do is building on the shared experience they have, to stress their commonality and shared interest. To some extend that seems to be the case for blogs as well, especially if they address a community that is somewhat interacting. However at least I would already be quite happy when we can detect the more superficial topic automatically.

Lilia equates the topic with the tag you would be putting on document like a blog. She has a point, but I would think that a tag's primary purpose is to make it possible to find something back by generating enough and sufficiently general associations (mirroring the precission recall dichotomy in information retrieval). On the other hand I think that, when asked the question "what are you talking about" I think they will try to give characterisation that is sufficiently precise in a given context. In a sense this may explain why Anjo is succesful with a simple information retrieval measure like TF/IDF, which is after all designed to find terms that are distinguished in a document compared to other documents (the context !). Without having read the full conversation a word like Blogwalk, Sigmund or Skype, may be quite enough as a characterisation. On the other hand Lilia, who has been engaged in the conversations, has more of a context. She will therefore subconsciously remember similar dicussions and change her context correspondingly.

Now what do I mean by similar discussions? I wish I knew exacty, but lets take the discussion on skype and pressence as an example. They both have high frequency and high TF/IDF in this discussion. In falling measure of TF/IDF score Anjo finds presence, Skype, communication, IM (= Instant Messaging, I guess), communication tool. Knowing Lilia, I know that she knows, that skype is a communication tool that supports instant messaging and presence, and that presence is the capability to tell whether you are avalailable for communication (so there you have ontological relations). Now what does it mean that Lilia remembers similar discussions. I don't know exactly ofcourse, because I don't really know everything she has read, and moreover the human brain is subtle. But let us suppose that using her ontological knowledge she will first "score" a hit for communication tool for every mention of skype, and score a "bit of a hit" for presence and quite a bit for communication (because this subject is dear to her hart). This puts communication tool, presence and Instant Messaging higher up the list. Again knowing Lilia, I know that she read blogged and talked about these subjects. Thus, consiously or subconsciously, I think she subconsciously changed her context (if you want to think in IR terms, changed the "document collection in which to compute TF/IDF scores) and asked herself what is it that characterised this dicussion in this more specialised context. In this context (and her social and blog circle) skype, IM and presence are not so characteristic anymore, so my guess (not having read the discussion) is that she comes up with a characterisation like

presence with skype

or likely more specific characterisations such as

How do you switch on presence in skype

or

presence in skype is really great/awful/mediocre

or

skype now does presence too !

or

......

It is thus not so surprising that she wants to have a Sigmund type cooccurence analysis of the conversation, because cooccurrence tends to emphasize the relations between terms rather than just the terms themselves, although being a statistical method, it cannot really see what kind of semantic relations may underly observed cooccurences.

Now I hope I know Lilia well enough, that my belief that she does not mind me blogging about what she thinks, is true :-).

The nonsense of 'knowledge management'

2005-11-02T03:23:00.000-08:00

Yesterday Anjo Anjewierden and I noticed that my blogs hardly, if ever, mentioned knowledge management. Today Olga Steen pestered me to look into knowledge management journals. This made me stumble into this blistering but IMHO mostly accurate analyis of knowledge management of professor TD Wilson as a cut and paste replacement for information management and training from management consultancies. Fortunately that didn't stop Anjo and me from having a fruitful discussion on how to get a grip on (proxies of) knowledge flows.

Jephte, an oratorium by G. Carissimi, september 17, 2005 11h, Jacobus Kerk Enschede.

2005-09-12T09:25:00.000-07:00

My choir montessera, the soloists Ilse van Griensven, Govert Valkenburg and Steffen Posthuma will perform Jephte, a beautiful oratorium by G. Carissimi (1605-1674). The choirs Il crocodillo cante and kamerkoor twente will perform "Musikalische Exequien" van H. Schütz. Both choirs are conducted by Jeanet Bosch. The performances are part of the Enschede Muziek Festival . You need a festival button to attend this, and many other performances. Choir members, like me, sell them for 5 euro.

time : saturday september 17 2005 11:00h.
location : Jacobus kerk Enschede
requires : festival button for 5 euro

Carissimi's oratorium Jephte is something like a small opera. The storyline, indeed large parts of the (latin) text, come straight from Judges 11. It is a dramatic story. Jephte (Jephthah) is called upon by the people of Israel to lead them into battle against the Ammonites. If you have just read Judges 11, you know that Jephte has an axe to grind, being the illegitimate son of Gilead and having been send away from his ancestral home for that reason. We are also informed that the casus belli echos problems we are only too familiar with in 21st century middle east: fertile lands have been promised to different people by their different gods. In Carissimi's Jephte this information is ignored. The historian (sung by the bass Steffen Posthuma) merely explains that the Ammonites have not been behaving reasonably and that Jephte is forced to lead Israel into battle against them. Then the central drama is set in motion: Jephte (sung by the tenor Govert Valkenburg) promises to sacrifice as a burn offer (holocaustum) the first being that will come from his house (primus de domo mei) if he is victorious. It is a solemn oath to plea for the favours of a jealous God. Jephte needs all the help he can get, and Israel is in great danger but it is a reckless gamble none the less. My girlfriend told me that her mother would tell her that Jephte expected his little dog to greet him. Cruel enough for a child, but Jephte lives in an age when human life had a different value, certainly of less value than honour and glory.

Jephte goes into battle and fights. He and his army drive back the heathens (fugite!, cedite! impii!, flee!, backward!, thy heathens!), and the Ammonites run for it (corruite). Twenty Ammonite cities are wiped of the earth in one big sweep. Finally, the Ammonites are humiliated before the Israellites while loudly lamenting their fate. Interestingly, Carisimi makes this "ululantes" sound very sad, it is the victims that we hear lamenting. An alternative interprestation is that victory marks the point where there is no going back and fate will take its inevitable course. Jephte promised sacrifice to God on victory, and God has delivered. In the next "scene", Jephte lives his finest hour: all of Israel is praising its leader in war who bestowed them with glory, honour and victory (laudemus belli principem, qui dedit nobis gloriam et Israel victoriam).

Returning home, his daughter, his only child, comes out of the door with tambourines to sing his praise. Fate has struck. Jephte immediately realises what has happened and cries out in pain to his daughter (heu, heu filia mea). His oath has entangled both of them in the web of fate (decepisti sum, et tu pariter). Jephte's daughter (sung by Ilse van Griensven) while seeing her father's anguish, fails to understand it (cur pater, decepisti sum). So Jephte, howling of sorrow, explains that he has sworn to God will have to sacrifice her in a burn offer. Jephte's daughter accepts fate. She offers herself as a sacrifice for the glorious victory of her father and her people(ecce, filia tua uni genita, echoing the ecce homo of Gods only son Christ) . She merely begs for one favour. Jephthe is only too glad to offer some comfort, however small, to her grave heart. She wants to go into the hills with her girlfriends to mourn. Jephte sends his daughter to the hills (Vade, filia). She mourns her virginity, mourns not bearing a son that will weep at her tomb, mourns not living life now that everybody rejoices victory. She wants the valeys and caves to echo with horrifying sounds, reminding me of natures reaction to Christs death so vividly described by the Blitzen und Donner in Bach's passion according to st. Mathews . In the grand final chorus (plorate filii Israel) all weep for her, the dissonants of the lamentamini making her pain audible.

The virgins lamenting Jephtes daughter

We spend a long time rehearsing the piece and it took a long time before the pieces finally came together. Sometimes, rehearing is frustrating, you feel like you don't make any progress. However, we have lots of good laughs in between, and I generally come home singing sotto voce and feeling happy after rehearsals, even after being scolded by Jeanet (our conductor) for not practising enough. And performing such a piece with the accompanying instruments, hearing how the main drama between Jephte and his daughter is unfolding between Ilse and Govert is enough to give you goose bumps[1]. We performed the piece twice before in a joint concert with Novafonie , and it was a great succes. I hope we will be at least as succesful this time.

[1] Steffen does a great Job too, but Carissimi has not given the historian as dramatic a role.

Anjo Anjewierden: Comment on Getting Wet

2005-04-06T07:23:00.000-07:00

In Anjo Anjewierden: Comment on Getting Wet Anjo describes a model of a blogging community as a network of pipes. We have been discussing this earlier and I originally proposed him an electrical model which is very similar physically, where links are modelled as resistors.

Actually I think the electrical network model is slightly richer. At first approximation you could make the "resistance" R of each link uniform say 1 Ohm. But on second thought there is also a characteristic time lag to be taken into account : the time in (days say) it typically takes for the reader to discover the link. In this electrical model the easiest way to model that (IMHO) is to to think of a blogger as a capicitor that is being charged. For a lag of a day with a 1 ohm resistor, the capacitance C would be 24*60*60 Farad. As is well known in electrical engineering, this makes the blog a frequency dependent purely imaginary node in the resistance network.

Z = 2pi sqrt(-1) f C

I find it sort of amusing that blogs turn up imaginary but as Robert Dijkgraaf pointed out in the NRC this weekend, nature is certainly complex. Every time a blog enters the network at time T that corresponds to an electrical (delta) pulse with spectrum exp( 2pi sqrt(-1) fT ) / 2pi.

Note that this gives the model two degrees of freedom : R and C.

This capitance model should give qualitatively different results from those of a pure resistor network with a more or less static current distribution. The reason is that the pulses contain lots of high frequency components and those HF components see little resistance in the capicitors. However at the edges of the network the pulses are smeared out and you effectively see a net avarage direct current component (this is how the rectifier in a computers powersupply works). That direct current component then trickles through slowly to other networks if they are connected.
What this models intuitively is that within a lively community the timescales for the spread of information can be quite different from that between the edges of two communities.

By the way we should only count links pointing _to_ a blog as they can be read by someone else and allow information to be passed on to someone else. In a related vein the model ignores the fact that information streams cannot be negative. We should just ignore this, unless we get large negative *average* flows.

Information overload

2005-01-13T00:33:00.000-08:00

Like Anjo I made some slides on information overload.

Information Overload

What is the problem ?

•
Information overload is a form of cognitive (over)load

•It comes from having to filter and judge more potentially useful information than a person can handle

•

Corollary : the Less is More principle:

–

There is a point where the extra benefit of providing more information is negative because it increases the cognitive load (cost) of getting at the more useful information.

–

The cost of not knowing may outweigh the cost of finding out.

Examples of Information overload

Overflowing mailboxes
•
Google queries with 12000 hits
so many (e-mails, papers, reports, meetings, conferences, blogs, documentation. memo's) to read/attend that there is no time to think anymore

What causes Information overload

•

Too much too insufficiently relevant information which technogy makes too easy to make available in ``raw'' form.
Anxiety to remain "in the loop'' and social pressure to keep people "in the loop".
Insufficient context: Judging and interpreting information is harder if you don't have the context of the producer. People often don't notice because they think the context is ``obvious'', and it is hard for Technology to preserve the context.

many children will explain things by giving an example. Sometimes giving an example seems childish but are good examples undervalued ?

What is the Result of Info overload ?

RSS and Dutch news papers

2004-12-13T10:25:00.000-08:00

Made a quick inventory of the use of RSS feeds with Dutch country wide news papers. The results are just what I can find from visually scanning their portals

Telegraaf : no
AD : yes
Volkskrant: yes (low key feature, it is very bottom of the page)
Financieel Dagblad : no
Parool : yes
Nederlands Dagblad : no
NRC : no
Reformatorisch Dagblad : no
Sp!ts : yes
Trouw : yes

the list comes from the link http://www.kranten.com

They also have a list of regional newspapers but I am too lazy to check them all out.

Far Wise in Knowledge Management: Blogging in your underpants

2004-12-13T10:24:00.000-08:00

I have been exposed by Carla Verwijs. Apparantly, I am not the only one who feels exposed in a blog though. Andy Boyd seems to share my feelings of unease. Blogs are such a public, persistent medium that I would rather err on the side of caution when deciding whether something is suitable for a blog. This is especially true when others are involved who may not like to find themselves blogged for semi eternity.

Robots can't throw, nor can women ;-)

2004-08-13T10:02:00.000-07:00

Found this website with some pretty impressive movies of humanoid robots moving in a very natural way. Surprisingly low cost too. But check out the movie where the robot throws overhand. The thing clearly throws like a woman. I have alway wondered why women can't throw. It seems that women just don't practice enough at girl age. According to this post it is not physiological, and that with training they can learn to throw "like a man". No offense meant but it is really remarkable how few women can throw well and how much better little boys are at it than little girls. I readily believe it is not a physiological distinction between man an woman that explains the difference but throwing also requires an extreme form of muscle coordination by the small brain. During the throw there is simply no time for feedback control of your arm, so your brain must send a train of coordinated pulses to your muscles. I can imagine why throwing skills are more important for men than for women evolutionary speaking. Anyway, it might be fun to see if robots are "fysically" challenged or that there programming is just not subtle enough.

© Copyright 2002-2004 Rogier Brussee.
Sometimes I write about things related to my work, but the views expressed here are my personal and do not necessarily reflect the views of my employer.

In memoriam Andrei Tyurin : Verdier Duality and Localised Euler classes

2004-08-06T08:12:00.000-07:00

Dedicated to Andrei Tyurin.

Andrei Tyurin had a profound effect on my mathematical career. While I was writing my thesis I ran into a review article on the differential classification of algebraic surfaces that was clearly written by some body who like me at the time had an algebraic geometry perpective (and from some one with a very deep insight and working experience too ! It was from this article that I learned the analogy between the Abel Jacobi and the Donaldson correspondence for example). It focussed on ideas, some of which were quite wild, and contained inventive new words like "topomodel". He is also one of the people in the mathematical community I really miss, so it was a shock to find that he died in oktober 2002.

I first met him (and Victor Pidstrigatch) on a conference in Goettingen organised by Stephan Bauer and Tom Dieck in 1992. I will never forget his enthousiasm trying to explain the spien poolynoomial invaariants, with his heavy Russian accent, waving his massive arms below his grey beard, and struggling with his English (which improved dramatically in later years). IIRC we also talked a little then. At the time those invariants seemed mostly a trick to get differentiable classification results for surfaces easier because the computation for spin polynomials involved only vector bundles with a section (how little did we see the value of the Spin structure back then, although later Victor told me that he toyed with the idea of doing something useful with that extra parameter). Later that year he came to see Oxford and he was very interested in my work on the pure Hodge type of the Donaldson Polynomials which fitted well with his own ideas on differentiably invariant lattices in the intersection form.

But at least as important is the fond personal memories I have. Despite being 20 years older than me, I got along with him very well. He was a very friendly man, with both a lot of humour, and erudite wise opinions. I remember a conference on the campus in Sophia Antolis. Andrei, a bunch of other vector bundloscenti (Steve Bradlow, Manfed Lehn, Oscar Garcia Prada ? ) and I collected coupons to drink very cheap wine and gossiped and talked math till late in the evening, enjoying the wonderful weather. I remember how much fun we had swimming in the mediterenean in that lovely place Cetraro (which with all the Italians and Fabrizio Catanese around was a merry place, and a very good summerschool) and that I discovered that he lost most of his toes while climbing in the caucasus. I also remember strolling through Bonn with him where he gave fatherly advise on our impending second child, or that he came to see us for dinner in Bielefeld, the house slightly smelly from the nappies of the children.
Having left mathematics without having said goodbye to him is so sad.

One idea that I can ultimately trace back to him and Victor Pidstrigatch is localised Euler classes of infinite dimensional bundles. In fact the first discussion I had on infinite dimensional Euler classes must have been with Victor on that that conference in Goettingen. I defined these classes with much more work on a much more hoc basis (and only for Banach manifolds ) in The canonical class and the $C^\infty$ properties of Kaehler surfaces. They were independently invented and refined by many people around the same time, mostly in the context of Gromov-Witten invariants, but the first account of them is in the context of Donaldson theory in the work of Pidstrigatch Tyurin (in I think [1]). I have been thinking about localised Euler classes in the context of Verdier Duality recently, so I think it is apt to write on some of those ideas here. If you the rest makes any sense to you then TeX should make sense as well so for the moment I will just leave it like that.

Let $\pi: E \to X$ be vectorbundle with a section $s$ and zero section $s_0$ over a locally compact space $X$. Then Verdier duality at end boils down to the fact that for a continuous map $f: X \to Y$, the pushforward with proper support $f_!$ functor has a adjoint $f^!$ on the full derived category $D(X)$ of (cohomologically constructible ?) sheaves. It is tradional to make some extra finiteness assumption and work with the bounded derived category, but with the approach to duality using Brown representability this assumption can be avoided.

let $\D_\pi$ be the relative dualising complex. It is well known that for a vector bundle of rank $r$, the complex is quasi isomorphic to $(or E)[r]$. We now define the Thom class
$$
\theta \in [{s_0}_! \Z_X, \D_\pi] = [\Z_X , s_0^!\pi^!\Z_X] = [\Z_X,\Z_X]
$$
as the class corresponding to $1$, which by the explicit form of the dualising complex is essentially the same thing as the "usual" Thom class of a vb (in fact we might take any fibration with a section e.g. the fibrewise cone of a spherical fibration and presumably get the Thom class and ultimately the euler class of the spherical fibration). Now pull the Thom class back with $s$, to get a localised Euler Class
$$
e(E, s) = s^*\theta \in [s^*{s_o}_! \Z_X, s^*\D_\pi]
$$
This is not a very nice group to work in, so we massage it into something more maneagable. The base change formula for the diagram
$$
\begin{matrix}
Z &\to ^i & X
\j \downto & &\downto s_0
\ X &\to^s & E
\end{matrix}
$$
implies that $s^*{s_0}_! \Z_X = j_!i^* \Z_X$ and $i^*\Z_X$ is just $\Z_Z$. So we get
$$
e(E,s) = s^*\theta \in [ j_!\Z_Z, s^*\D_\pi] = [ \Z_Z, j^!s^*\D_\pi]
$$
This class already lives clearly on a group assoicated to $Z$, but let us rewrite it further.

Assume there is a complex $Ind \in D(X)$ such that $s^*\pi^! \Z_X = (Ind, \D_X)$ where $\D_X $ is the Verdier dualising complex of $X$ (i.e $D_X = p^! \Z_{pt}$ where $X \to^p pt$). For example if all complexes can be represented by bounded and finitely generated groups then $s^*\D_\pi = (s^!(\D_\pi,\D_E),\D_X)$. Also on a manifold of finte dimension $d$ we know that $\D_X = orX[d]$ and we get $Ind = or(E)^* \tensor or(X) [d-e]$ so $Ind$ for index is quite appropriate. Then since
$$
j^!(Ind, \D_X) = (j^*Ind, j^!\D_X) = (j^*Ind, \D_Z)
$$
(an adjoint of the projection formula) we finally find that
$$
e(E,s) \in [ \Z_Z, (j^*Ind, \D_Z)] = [j^*Ind, \D_Z]
$$
So the localised Euler class lives in ""twisted locally finite homology" and because this construction is functorial, it is certainly the "right" way and the right group to define the localised Euler class in.

Now infinite dimensional spaces are of course not locally compact, but using the full derived category, it may well be that this assumption is not really needed for the duality machinary and the computation above would work. The existence of $Ind$ in the bounded derived category $D^b(X)$ should be the proper definition of a Fredholm section, and the usual Fredholm condition should be enough to guarantee the existence.

[1] Invariants of the smooth structure of an algebraic surface defined by the Dirac operator, Izv. Ross. Akad. Nauk Ser. Mat. 56 (1992), no. 2, 279 English transl. in Russian Acad. Sci. Izv. Math. 40 (1993), no. 2, 267

© Copyright 2004 Rogier Brussee.
Sometimes I write about things related to my work, but the views expressed here are my personal and do not necessarily reflect the views of my employer.

Kunst Uitschot Team Part II: The return of the sculpturer

2004-05-12T10:47:00.000-07:00

My brother Barthel Brussee is an artist. As long as I can remember, he used to draw and as a teen he made his own comic books. These days, his paintings and graphics are quite nice, I think, and I have actually bought a few of them.

His new thing is the
Kunst Uitschot Team (something like Art Scum Scene). The Kunst Uitschot Team secretly and illegally hacks in the middle of the night. They don't hack computers but big oak poles that they transform into sculptures. For example they created this six toe foot sculpture on the Dutch beach between Katwijk en Wassenaar of one of the beach poles. Unfortunately Rijkswaterstaat sawed it off because they didn't like the idea of people changing state property. Not to be outdone, the team just put a new sculpture on the sawed off pole.
They also put a Venus from Leiden in the middle of the Leidse plantsoen park, close to the Dutch branch of Cetim. If you listen to the interview made on the beach it should be clear their work has as much to with the performance as it has to do with making art. And of course, they want their share of the 15 minutes of fame, and they want to be ARTISTS!

Anyway, at Koninginnen dag (30 April) my kids and I found my brother and the rest of the team chipping away on a pole at Leidens Townhal square This being koninginnendag, everywhere around them, people where listening to music, doing garage sales, plugging their book, or just enjoying the lovely weather (see this movie). His kids and wife were around too. Clearly his kids where not quite as impressed as the admiring crowd they had gathered around them though. I don't know if the statue is still there. They planned to leave it right there at the square, and made it impossible to be removed without brute force, but perhaps the authorities have flexed their muscles.

Note to self: make an appointment with B. next time I go to Leiden.

update 17/5 : I went to see my brother this weekend and he showed me the teams latest creation, unimaginatively called number 9. By the way, the statue on the townhal is still there.

update 29/5 : The Leiden local council has decided to remove the statues. Go sign the petition supporting their stay here!

Devilish Definition of the Semantic Web

2004-03-25T08:30:00.000-08:00

Finally read the proper defintion of semantic web by Danny Ayers.

March 22, 2004
Devilish Definition
Semantic Web, proper noun

An attempt to apply the Dewey Decimal system to an orgy.

The Devil's Dictionary (2.0)

Save the planets!

2004-03-17T01:35:00.000-08:00

So they say that a new planet called Sedna (2003 VB12) has been discovered. Therefore all astrological computations have to be redone and life takes a completely different course, right ? According to the discoverers, Mike Brown (Caltech), Chad Trujillo (Gemini Observatory) and David Rabinowitz (Yale) my life willl change course but for an unexpected reason. Sedna is not a planet, but a planetoid. It is just a large object in the inner Oort cloud, almost certainly not more massive than the rest of the Oort cloud put together. Maybe it is not even the largest one in this class. However they also argue on similar grounds that Pluto should be demoted to the status of planetoid and is just the largest Kuiperbelt object.

Astrologists of all nations, unite! Save the planets! If this continues what remains certain in life?

Croeso: Google within companies?

2004-03-15T09:40:00.000-08:00

In Croeso: Google within companies? Andy Boyd comments on the fact that Google does not work particularly well for the intranet because most of the information is in databases mailinglists and ERP systems. I am a little surprised about the mailinglists (I guess there are just no external links to the posts in the archive and the mails do not link to each other well enough), but that the databases are overlooked is completely expected. The thing is, Google does not work very well for the web either because most of the information on the web is in databases too. You usually donot realise this because google does not find it for you, and on the web you know less well what ought to be found. This is called the deep web phenomenon. People estimate that most of the information on the web is actually hidden in the deep web. Some people say its 99 % of teh information but it all depends on how you measure things. The human genome accounts for lots of bytes on the web but I donot think every gene should count as a webpage.

But Google is smart and they want to go IPO right ?

The people at Google are very smart indeed and google does an amazing job at what it does, but it is not clairvoyant. Google even has no understanding of what it reads, it just does some statistics. Now suppose you are 13 3/4 years old and want to know the production of the norwegian leather industry. If you poke around with Google you eventually find this

http://www.euroleather.com/database.html

It is a webpage, on the internet, it wants to be found. I could find it only by asking google to look for leather production and database. Google found a page containing leather and a link called database. The database has a pull down menu containg Norway. I.e. found the page above by outguessing the system and a little luck. But what should have happened is that

the database describes itself to the world and particularly to google as

1. it contains information which you can query on a geo:country in geo:Europe and optionally on leather:tannery and the following list of goods,
2. it returns the amount of leather:leather in unit unit:tonsPerYear
3. it has a well defined interface

Google should "know", having indexed the geo ontology, that Norway is a country in Europe.

Then google could query the database for you and you would get the answer. The possibility to self describe a information source (in terms more general then simply listing all its entries) is a key challenge for the semantic web. Apparently Amazon and Google do something like this already. With such a delegation model you have a much cleaner division of responsibilities.

Thirteen

2004-03-15T03:19:00.000-08:00

Last week my girlfriend and I went to see Thirteen. It is a disconcerting movie because you see how easy it is for a sweet teenage girl to get lost in the wide wild world. Actually I also felt sorry for the the mean teeange girl who is depicted as a having had every possibility to get damaged by life. Incidentally the mean girl is played by the girl who wrote the script and who had the sweet girls real life experience. I remembered that while celebrating my own daughters birthday. She is getting to be a big girl. Fortunately it was just a passing thought, we didn't let it spoil the fun.

Getting an RSS feed

2004-03-15T01:04:00.000-08:00

Lilia kindly pointed me to this site which allows me to have an rss feed from my atom feed. Basically it is a little service that takes my atomfeed and converts it to an rss feed Like so:

http://www.2rss.com/atom2rss.php?atom=http://www.2rss.com/blog/atom.xml

Thanks Lilia !

The relative importance of things

2004-03-12T01:12:00.000-08:00

BBC NEWS | Europe | Spain mourns train attacks dead

The shocking news form Madrid makes you realise the relative unimportance of all our elegant little arguments

On the classification of Weblogs

2004-03-10T09:16:00.000-08:00

This is the result of a brainstorm session on the blogging phenomenon and on the classification of weblogs, which I had with Henk de Poot

We distinguish three different types:

P:: the personal weblog, the personal voice of someone.
A:: an aggregation of personal weblogs,
C:: community weblogs, basically they are mailinglists NG, or the voice of a whole community.

Those types are roughly in ascending order of publicness.

The personal weblog is the weblog "classic" . Somebody writes a diary or simply makes public what he/she is interested in.

The aggregated weblog is a more recent phenomenon, and seems to be taken up mostly by the hardcore hacker community. Aggregation at the personal level is part of the core business of the blogger to make his/her life easier while trying to follow what goes on in the bloggosphere, by simply selecting the RSS feeds of those bloggers he/she wants to follow. However the mechanism can clearly be reused for first aggregating the rss feeds of a few bloggers and then pushing the combined feed back out to the world. Crucially, writers of aggregated weblogs subscribe to the aggregation channel log themselves, although there will often be a moderator who decides whether the blogger really belongs to the community or not. Thus it is an active act of choosing the community in which one wants ones voice to be heard, and it seems that the posters to the aggregated list read the list themselves and react upon it. An aggregated blog has a much “louder voice” and it can therefore be easier (and possibly more prestigious) to be heard as an individual inside this channel. On the other hand it also easier to get drowned out by the rest of the crowd. I guess it is a matter of scale: if the channel is open for too many people it looses it's distinghuishing feature and the signal to noise ratio drops too much. But my guess is that it is the same phenomenon is at work that accounts for competing shops crowding together in a mall or the synchronised flashing of certain tropical fireflies to attract females: those you want to attract go where the action is, so you have to be there yourself.

Examples planet rdf, planet gnome .
(Both are very nerdy sites but especially in the latter people also tell about the bloggers lifes outside of their frantic coding activity)

If blog entries can be (and are) given keywords (or semantic categories), then there is also the possibility to filter on keyword, and mutatis mutandis to aggregate on that basis

Example

my Girls and Beer blog

my Political Blog

my knowledge mgt blog

my company blog

my Movies blog

Ofcourse some blog entries can go to several channels simultaneously. I am not sure whether this works in practice, because it assumes that people tag their logs with keywords, or that reasonable automatic indexing takes place.

Root systems

2004-03-04T02:23:00.000-08:00

I realised two things about root and weight systems that I could have realised years ago.

The first realisation is that for a representation V of a Lie algebra g with maximal torus t, the weights of V can be identified with the support of the sheaf V^~ obtained by localising the S^* t module V over the scheme t ^*= spec S^* t. For semi simple Lie algebra's this space consists of reduced points and the restriction of V^~ over a weight lambda is just the weight space V_λ. To prove this, write

v = ∑ v_μ

in the weight decomposition. Then if t -< λ,t > 1 is a hyperplane on t ^* vanishing in λ, we have for all n

(t- < λ,t >)ⁿ v = ∑_μ (t - < λ,t > )ⁿ v_μ = ∑_μ (< μ, t > -< λ,t > )ⁿ v_μ.

If v has support in λ then (t-<λ,t>)ⁿ v = 0 for n >> 0 and we see that all v_μ =0. Conversely, if all the v_μ are zero for λ ≠ μ (so v = v_λ), then (t-< λ,t > ) v = 0. Therefore v has support on λ and the support of the sheaf V^~ is reduced there.

The other realisation I got from the wikipedia is that the exceptional root system G₂ is just the configuration of the star of David.

A touch of Kant

2004-02-18T05:40:00.000-08:00

Yesterday, I went to listen to a lecture on Immanuel Kant organised by the university of Twente . To my surprise it was very crowded and I had to sit on the floor. Kant died 200 years ago and there should be some attention to him over the year. from what I understood, his ideas about the knowability of the world are still supprisingly fresh.

One of his prime ideas is that the way we talk about the world is rooted in experience and the rules that govern reality. For example every material entity can only exist at a certain place and a certain time. However our mind can abstract from this in that it can live with the idea of a space and time (or post Einstein space-time) which has an existence independent of the entities that are in it. Once we have made this induction and having figured out the rules of the game, we can start imagining things that could happen, rather than things that did happen. Moreover since other people also share the experience of living in a space at some time we can at some point communicate soundly about such an abstract idealised concept, talking about its properties even if it only could or should have an instantiation, instead of actually existing.

Now if you try to do knowledge representation you are faced with a similar situation. You have to develop concepts to organise the world. The concepts have rules and relationships between them, which allows you to argus about them. You often want the relationships to model realworld relationships between instances of those concepts, but typically you would want to talk and argue about instances relationships that could rather than do exist.
The reason is that existence proofs are difficult (ask any mathematician), infeasible (go query every database in the world), or you are just preparing for the future. Therefore in knowledge representation you end up with having abstract notions, that need not have any instatiations, or whose precise instantiantions you don't care about.

If you read up on RDF and OWL you realise that the RDF and OWL classes are very much of the could exist categories rather than must exist. This is as it should be. Unfortunately the formal underpinning of those languages in the model and syntax is on the level of set theory. Superficially this makes sense. The rdfs:Class Car seems mathematically modeled on the set of all cars. Also the rdfs:Property numberOfWheels seems like a relation between the set of cars and the non negative integers. Well we certainly want to be able to talk about next years cars too, so it is more like all cars that could ever be or all things with an engine and four wheels that you can park in front of your house. Now we get into trouble. The rdfs:Class Car looks more and more like the set of all sets that gives you the Russell Paradox showing that there is no such thing as the set of sets. There seem to be a lot of restrictions on OWL (Description logic version) and RDF to avoid Russels Paradox, but still, there seems to be something conceptually fishy with modelling classes as sets and having everything in a fixed universe. Sets are equal if the instances are equal and this is just not a useful model for the classes that you model. They seem really more like well classes. Dont get me wrong though, a universe a fixed set of all "things" which also contain the subsets of all the sets in the universe is a sound thing, and it is used with virtuosity by no less than Grothendieck for example.