This page contains a personal account of the world's first conference
entirely devoted to Data Compression: DCC'91. The conference was held
at Snowbird, Utah, USA, 7-11 April 1991. This document was posted to
comp.compression on 20 May 1991 and was put up for FTP
in my compression archive. This page consists of that original report with
some spelling errors corrected and with additional comments which were
added on 5 May 1996 in the form [05-May-1996: ...].
The original pure-text document is available as follows:
Please bear in mind that this document was written at least five years ago. Nowadays, I might write this differently. Also, please do not assume that just because I have added corrections, that the rest of the paper represents a statement of fact, or even my current opinions. I added comments in a hurry and might have missed something.
By Ross Williams, 20 May 1991.
This document gives a personal account of the world's first conference entirely devoted to Data Compression: DCC91. The conference was held at Snowbird, Utah, USA, 7-11 April 1991.
The first thing that one notices as one flys into Salt Lake City, Utah is that it is flat. Very flat; except that is, for the enormous mountains surrounding it, upon which snow falls thick enough and often enough to provide almost year round skiing conditions. In the heart of a valley in the mountains surrounding Salt Lake City lies Snowbird which is an enormous ski resort. Right in the middle of the enormous ski resort is an enormous hotel called the Cliff Lodge. The conference was held there.
The focus of the Cliff Lodge is an enormous ten story atrium which I suspect was originally designed to hold Saturn V Rockets. The atrium has an enormous glass window which faces onto the mountain where most of the skiing happens. There is usually something interesting going on. The effect is stunning.
On the other side of the lodge is the beginners slope and the ski rental shop. Rising up the mountain is a large cable car and a chairlift. The cable car would go up and ten minutes later the bottom of the mountain would be flooded with skiers. This would go on all day. In the morning there were loud explosions as the snow teams blasted away excess snow. All in all an excellent place to go skiing.
The conference program was roughly as follows:
Sunday 7 Registration and reception. Monday 8 Papers and banquet. Tuesday 9 Papers and poster session. Wednesday 10 Papers and rush off to the airport. Thursday 11 NASA/Navy Workshops.
About 150 (from memory) papers were received for the conference. 44 papers were accepted for presentation and there were 42 papers in the poster session. The conference seemed to be about 1/3 image compression, 1/3 text compression and about 1/3 coding and theory.
Here is a copy of the programme. My commentary continues after the programme...
Note: There was also a list of delegates but I am certainly not going to type all THAT in as well!
The conference started with the registration and reception. This was a highly charged occasion as many (if not most) people there were meeting everyone else for the first time.
As far as I could tell, there was a solid core of academia (the hard core?) who were surrounded by dozens of curious industry representives most of whom seem to have come to sniff out new people and algorithms to compress their ever-increasing volumes of data. There were also a lot of space and science types there trying to work out what to do with all the signals coming back from out there. Altogether about 256 compressor heads.
Most of the conferences I have attended at the past have been geographically defined and I have found them to be largely a waste of time. Someone gets up an explains his latest lemma in the non-linear theory of complex meta-widgits. Then someone stands up and gives a vague overview of an ongoing 20-person research project. Nobody understands what anyone else is saying so they all get drunk and go home.
In contrast, DCC91 was a remarkably tight conference. Hundreds of people who had never met each other seemed to mix well. The people present were from many backgrounds, but all shared the deep psychological need to make data smaller.
If anything, the major division was between the SIGNALS (who want to compress images, sounds and other signals) and the TEXTS (who want to compress text data) (see section 1.14 of my book for a tight definition of the distinction). These two groups, while sharing the same basic semantic vocablary, sometimes seemed to be on different planets. As far as I could tell there were about 2 SIGNAL delegates for every TEXT delegate. There seemed to be a trend towards image compression. Many TEXTs (including myself) seemed to be a little envious and curious about the techniques so fluently bandied about by the SIGNALS and I think we will see some defections next year. This is a healthy trend, as images are likely to end up taking far more space than text in the long run.
I met lots of interesting people. As well as meeting academic greats such as Abraham Lempel and Ian Witten, there was a soup of industry people from many different areas all with different stories to tell. I met an oceanographer who was looking to compress data about the ocean. He could measure the height of the ocean to within a few centimetres. One guy was from a company that manufactures video games. Another was from a company making fax machines. There were several people on satellite data projects. One large software company was there partly to sniff out ways to crunch up programs so as to save on the distribution media. Another was there to find new algorithms for data compression products. One guy was on a project that was going to collect SIX PETAbytes of data -- I had to go and look it up. The scale goes like this:
10^3 Kilo 10^6 Mega 10^9 Giga 10^12 Tera 10^15 Peta 10^18 Exa
You would have about six petabytes of data if you gave half the population of Australia a different compact disk each. However, this would make it very hard for disk jockeys to choose songs so do not attempt this in your own country.
Food at the Cliff Lodge seemed to be the usual combination of fairly high priced restaurants and overcrowded discount snack bars with nothing much in between. There was a reasonably-priced restaurant nearby but one had to wade through the beginners slope to get there. Luckily, one could survive for much of the time on the rather generous snacks presented during the conference registration and poster sessions.
I observed an interesting effect during the (I think) poster session where the hotel served a variety of main-course snack foods and a chocolate cake cut up into slices. The chocolate cake moved slowly at first and then was observed to vanish at an exponentially increasing rate. This could be because:
However, what I think was happening was that everyone had their eye on the chocolate cake, but didn't want to eat any until they had finished their "main course". However, when the cake started disappearing, the prospect of missing out caused lots of people to abandon this ideal in favour of securing some of the scarce resource. So it was (2) with a sort of added criticality thrown in. Maybe we could use some catastrophe theory here. Anyway, it doesn't matter because they brought in another chocolate cake.
As a general rule, the food got better and better as the conference went on.
One of the dominant underground themes of the conference (at least for me) was PATENTS. As Richard Stallman has pointed out, the situation with software patents is getting on the stupid side. Amazing though it is, there are now software patents covering:
These are just the beginning. Soon, it seems, it will be impossible to write a large computer program without accidentally violating several dozen patents.
The field of data compression is now hot with patents. Starting with the problems with LZW (Unisys wants about $20000 from any manufacturer using it) and Unix compress, we have seen the LZ78 hierarchy almost closed to the public. It is extremely unclear what is covered and what is not.
A key issue here is that there seems to be no TECHNICAL procedure for establishing exactly what a software patent covers. It seems that any company that has a patent coming remotely close to an algorithm in use can successfully launch (if not win) a lawsuit against the user. This environment rules out the use of any algorithm close to a patented algorithm by any company or individual who could not survive a test law case. One result, as we have seen, is the locking up of the LZ78 hierarchy.
I went to the conference expecting to find the answers to the question of what is covered by patents and what is not. Instead I found hundreds of people even more confused than I was. In the twilight hours of the conference dinner I remember sitting at a table with some fairly heavy compressor heads none of whom seemed to have the faintest idea of what was covered by patents - "Only a lawyer can decide" they said.
From my communications before and during the conference my impressions of the patent situation are as follows [05-May-1996: Author accepts no responsibility for these opinions]:
You can find out more about software patents and their problems from:
The League for Programming Freedom 1 Kendall Square #143 PO Box 9171 Cambridge MA 02139 Net: firstname.lastname@example.org Phone: +1 (617) 243-4091 Document: "Against Software Patents". Document: "Against User Interface Copyright".
[27-Jul-1998: The League For Programming Freedom no longer exists.]
To "raise the consciousness" of participants, James Woods and I handed out league for programming freedom propaganda and buttons (reading "Get Your Lawyers off My Computer"). We received various responses ranging from that of someone who seemed to have just come from the live audience of the Arsenio Hall show ("Hey yeah, give me that badge - yeah, wooo woo wooo, ooh ooh ooh") to the gruff refusal of a guy from a certain big company who had probably come to the conference to flog patent licenses. Gruff refusals were also obtained from people whom we had already bothered three times before - its hard to recognise the people you've already approached out of so many people!!
Most people at the conference seemed to agree that there was a serious problem with the patent situation, but did not quite align with the League for Programming Freedom whose current short term goal is the elimination of all software patents. Nevertheless, it was gratifying to see much of the room wearing the badges by the end of the poster session.
The conference was abuzz with standards, particularly in the SIGNAL field. Standards for TEXT compression seem to be sparse and confused (Unix compress and MNP5 are the only ones I know of) probably because of the problem with patents. However, the SIGNAL field seems to have lots of standards. In particular, everyone seemed to be talking about a new JPEG standard for image compression and there seemed to be a lot of job opportunities for anyone wanting to get involved with JPEG.
I'm sure by now, you're sick of the conference, and so often were the delegates - which was why holding the conference at a ski resort was such a good idea. The conference organizers, being (apparently) avid skiers organized the program so that there was a four hour lunch each day from 12pm to 4pm.
On the Monday afternoon, I fronted up along with a few other compressor heads for the beginners skiing class. Skiing starts on a very small (but fairly steep) learners slope and then progresses to the beginners slope which has a small chairlift. When I saw this chair lift I couldn't believe my eyes as there was no forward guard rail of any kind. One gets hoisted up into the air a good thirty feet (est) with nothing to stop one from falling forward. I am amazed that they can operate the lift day in day out without people falling off all the time and killing themselves.
All went well for the first three hours - I didn't fall (off the skis or the chairlift) once - until just near the end of the session at 4:50pm I let out the throttle a little at the top of the beginners slope and fell over. Not to be discouraged, I got up and kept going but got out of control. The only method of stopping I knew was the snow plough method and it was just not working. As I gained speed, my attention was drawn from attempts to stop to navigation. As I rocketed down towards the end of the beginners slope three options presented themselves:
Middle: A narrowing flattening run of snow leading to a plaza.
Right: The very beginner's ski slope leading further down (steep).
In these situations there is always the little kid. Tradition has it that whenever one comes a cropper skiing, a little kid comes whizzing down the slopes, does a perfect snow spraying stop, and then says: "Gee Mister, Are You OK". I assured him that I was. Later I discovered a couple of blood knees, some bruises, and pants torn at the knees.
This experience put me off skiing for the remainder of my visit (but only just). The thought of giving my presentation in a plaster cast did not appeal to me - and I certainly would have been doing that, I was assured by many people, if the safety clamps on my skis had not activated. Also, I find that I feel basically unsafe with the bottom half of my lower leg locked stiff to a right angled piece of metal and fibreglass; it just feels perfectly set up for a broken leg. Nevertheless, skiing is so much fun that I will probably be at it again sometime, maybe even at DCC'92 if I can get there. [05-May-1996: I got there in 1992 and I did ski!]
ADVICE: Snowbird is a great place to learn how to ski. However, apart from the lessons, one is largely on one's own. If you intend to attend DCC92 and try skiing I suggest that you:
The rest is easily hired. A few people including myself were caught short on some of these details as many people did not even know that they were going to a ski resort. I suggest that you take all the above stuff even if you do not intend to ski as you will probably end up doing so anyway - Snowbird's like that.
The climate at Snowbird is such that skiing is possible almost all year. During the conference the conditions were excellent.
Snow was a new thing for me. Most delegates from North America seemed to be highly familiar (if not bored) with it and enjoyed only skiing over the top of it. Having lived most of my life in the Australian heat, I relished the snow itself and found it fun to touch, eat, throw, kick and look at it - the first time in the snow for me in twenty years.
On the (I think) Wednesday it snowed all day and there were four foot snowdrifts everywhere. The snow fell so thick on my balcony that I was able to make a small snowman, with coins for coat buttons and eyes, the drinking glass cover for a hat and icicles for arms. I was amazed at the speed at which icicles grew on everything.
I presented my paper "An Extremely Fast Ziv-Lempel Data Compression Algorithm" halfway through the very last session of the very last day (4:50pm Wednesday). Numbers had thinned by this stage as many people had left to catch an evening flight (see ORGANIZATION later) but there were still a reasonable number left. Each presentation (including this one) was 25 minutes including questions.
I was unusually nervous for my presentation (first ever international conference paper presentation) and stuffed it up to a large extent by falling off the podium backwards while attempting to point to an overhead transparency, by muddling the slides, and by running at first undertime and then overtime. Despite this comedy relief, I think I got my message across.
One interesting aspect of the podium was that it had TWO overhead transparency projectors. This presented at least three options to speakers:
I chose the third option, using one projector to display "subliminal advertising" which I changed every few minutes during my talk:
Subliminal advertisement #1: BUY MY BOOK. Subliminal advertisement #2: DONT PATENT SOFTWARE. Subliminal advertisement #3: READ COMP.COMPRESSION.
and the other for the normal stuff. Despite the abundance of projectors, there was no table space on which to put things. Just a small metal tray on the side of each projector. This was very frustrating and made manipulating the slides for presentation difficult. I hope that this can be fixed for next year.
People seemed pleased with the practicality of my paper ("we love your paper - it's actually got CODE in it"!!!). Many delegates from industry seemed put off by all the mathematics and theoreticalness of other work. However, my glory was short lived as, after my presentation, Timo Raita strolled up and informed me of an even faster algorithm of 1987. This had me worried for a few days until I tried it out in Boston and found that it yielded 7% absolute worse compression. The competing algorithm still goes faster (compressing - slower decompressing) and the question mark of my alternative title "The World's Fastest Adaptive Text Compression Algorithm?" turned out to be spot on. A lesson in humility. For those who are interested, my algorithm (which still holds a minimum point on the compression/speed performance curve [05-May-1996: I don't know if this is still true]) can be obtained from [05-May-1996: The address has changed since this document was written. These are the new addresses.]:
As a side note my book "Adaptive Data Compression" (ISBN: 0-7923-9085-7) is available for US$75 from
Kluwer Books 101 Philip Drive Assinippi Park Norwell MA 02061 USA Ph: +1 (617) 871-6300 Fx: +1 (617) 871-6528 Nt: email@example.com
[27-Jul-1998: See the Thesis Book page for up-to-date details and online ordering.]
By Thursday, most delegates had gone home although a few popped up here and there. I didn't attend the NASA/NAVY workshops but I peeked in and there seemed to be about fifty people.
In general, the conference was excellently organized. Good organization is often not noticed because it manifests itself in the ABSENCE of stuffups and as far as I could tell, there were very few (if any) stuffups in DCC91. In particular, the conference proceedings were published in book form which was very neat and better than the usual 400 page loosely bound mountain one is usually lumbered with.
There was a bit of a fuss about the scheduling of the last session, as at least one delgate had booked an early evening flight and had to leave before their presentation slot. Throughout the conference there was fairly intense lobbying to move the final session forward into the four hour lunch break. It seems that the majority of delegates wanted the final session moved back. However, the conference organizers wouldn't hear of it. This caused some minor bad feeling. The conference organizers also came under fire for (apparently) booking the place for next year without telling anyone. Certainly Snowbird ski resort was a superb location for the conference and the organizers should be congratulated. However, there are many other superb locations in the world (and many other sports (I like skydiving so let's have it at Perris Valley!!!!)) and it seems only fair to move the conference around a bit. Maybe this can happen after the conference has attained a two-year identity.[05-May-1996: The conference is now well and truly established at Snowbird.]
As I understand it, the conference proceedings have been published by the IEEE and you can obtain a copy ("DCC91 proceedings") from:
IEEE Computer Society PO Box 3014 10662 Los Vaqueros Circle Los Alamitos CA 90720-1264 USA Ph: +1 (714) 821-8380
The proceedings are in the form of a small, strongly bound book and is essential reading for compressor heads. It may also be possible to obtain a list of the papers presented and then individual reprints.
This is roughly how my costs came out which should give a good idea for those thinking of attending next year.
Registration : About US$300 Accommodation: About US$ 90/night. Ski rental : About US$ 20/day. Ski School : About US$ 25/afternoon. Breakfast : About US$ 10 (in restaurant). Dinner : About US$ 25 (in restaurant).
A VERY successful conference. Congratulations to the organizers not only for organizing it so well but for thinking of having such a conference in the first place. If you have an interest in data compression or skiing and can possibly attend DCC'92 then try to do so.
This has been a very informal conference report. I had fun writing it. Please read it in the spirit in which it was written. Apologies in advance for omitting any obviously essential information or for offended anyone.
Copyright © Ross N. Williams 1996-1997. All rights reserved.