As an example consider a blog where users must be logged in to comment. In this system there is a create comment page. This page adds the comment, when submitted, to the article that the user was viewing before he went to the create comment page.

If application state was managed on the server, there might be a variable stored in the user account that identifies the post that that user last viewed. This variable would be referenced when the user submits a comment, with the comment being added to whichever article that variable contains.

Now, how can that go wrong? Say a user, let’s call him Steve, logs in to the blog. Steve reads an article that he would like to comment on, so Steve goes to the create comment page. While composing his comment, Steve remembers another post that was related that he would like to quote. So Steve opens a new tab and navigates to that post. Steve then goes back to the tab with the comment form, finishes it and clicks the submit button.

In this scenario, the comment, since it relied on the server side variable to determine which article the comment was for, would end up on the second article, the one Steve was viewing in the second tab, because that was the last viewed article, not the one he was actually trying to comment on.

In a better design, the article that a comment was meant for would be manged on the client side, it being application state, possibly as an item in the comment form.

Obviously this is a simple example, but generally the ways in which this problem arise can be reduced to such a simple scenario. They generally involve many more steps and much more complicated interactions, but they all involve requiring the server to know the current state of the client.

See also: State in Web application design

1. Web search is still pretty terrible once you need something more than a company’s homepage or a wikipedia entry. There is a vast wealth of information dispensed by experts everyday in venues that don’t attract large numbers of links. Finding that information is way more painful that it needs to be.
2. 99% of people writing about the REST style seem to have totally missed the most important constraint: Hypermedia as the engine of application state (HATEOAS). If that concept was better understood by more people we might finally make some progress on things other than how to make pretty URLs. It took a significant amount of time to discover just how important that constraint is for the REST style (very, by the way, like, it’s everything, no HATEOAS, no REST, not even close), and that really slowed down the design process for me.

Here is some HATEOAS link love so as to do my part to improve the state of knowledge on REST in those link counting search engines

• Roy Fielding on ROA vs. REST
• Roy Fielding on connectedness vs. HATEOAS
• Peter Williams on The Hypertext Constraint
• Subbu Allamaraju on Hypermedia and REST

He keeps going on the road, selling steadily, a few gigs a month, year after year. That may be why there are 1.4 million copies of his titles in print—a staggering figure for self-publishing. (The top seller, The Visual Display of Quantitative Information, has been a reliable mover since 1983.) And at these six-and-a-half-hour presentations, the audience starts cheering when he hits the floor, clamors for their books to be signed, buys posters at the table out front. As soon as the applause stops, Tufte bolts backstage, enthusiastically draining a Corona.

Turns out that this problem was easy to fix, all that was needed was to get the web server to return the correct HTTP status code. As it was, it was returning code 200: “OK”, when the more appropriate code would be a 503: “Service Temporarily Unavailable.”

All our customer sites run with an Apache server sitting in front of the Rails sites. This allowed us to make the maintenance page a script rather than just a static HTML page.

• To start, we implemented the custom maintenance pages described by Mike Clark.
• Next we replaced the HTML version of the maintenance page with a PHP page.
• And last was to add in a couple of custom headers into the PHP page so that it returned the correct information.

<?php
header("HTTP/1.1 503 Service Temporarily Unavailable");
header("Retry-After: 300");
?>


We included a Retry-After header of 5 minutes, assuming that the site will probably be back up soon.

And that’s it, a couple of changes and now our sites speak proper HTTP even when disabled, great!

The Agriculture Department said that its review of the database shows that between 100,000 and 150,000 people could be at risk.

Privacy advocates say the actions by the agencies may not be enough. The database is more than two decades old, and is used by many federal and state agencies, by researchers, by journalists and by other private citizens to track government spending. Thousands of copies of the database exist.

Make our webpage straightforward, and if possible elegant–and, no matter what, increase the amount of news available within the immediate eyespan of the viewer on the homepage. We want more of what we do well immediately visible. People come to our website for the news, not for the interface.

Edward Tufte
March 29 2007

Sage advice any site designer should heed. Click over to Dr. Tufte’s site to join in the discussion about the Post’s redesign.

Anyone who’s been a victim of “death by PowerPoint” - that glazed and distant feeling that overwhelms you when some sales droid starts their presentation - will be reassured by Aussie researchers who’ve discovered biological reasons for the feeling.

Humans just don’t like absorbing information verbally and visually at the same time - one or the other is fine but not both simultaneously.

Researchers at the University of New South Wales in Australia found the brain is limited in the amount of information it can absorb - and presenting the same information in visual and verbal form - like reading from a typical PowerPoint slide - overloads this part of memory and makes absorbing information more difficult.

Professor Sweller said: “The use of the PowerPoint presentation has been a disaster. It should be ditched.

“It is effective to speak to a diagram, because it presents information in a different form. But it is not effective to speak the same words that are written, because it is putting too much load on the mind and decreases your ability to understand what is being presented.”

The theory of “cognitive load theory” suggest the memory can deal with two or three tasks for a period of a few seconds - any more than that and information starts to get lost.

Read the abstract of Professor Sweller’s work.

I worry that this site is trying to hard to be everything to everyone. Covering all types of data and trying to do something intelligent with them seems to me to make it unlikely that the site will be an authority on any data set. Also of concern is the highly likely possibility of users producing all kinds of bad graphs that mean nothing, but are treated as evidence of something or other. Those that enjoy the kind of nonsense graphics that populate the likes of Time magazine, will probably love this site for that very reason.

What is exciting to me, is the possibility of this site becoming a central repository of quality metadata. The kinds of datasets that are most useful as additions to other datasets. Things like lists of holidays or stock market closing days. If these types of datasets find a home on Swivel, perhaps they can get the ongoing updates, corrections and verifications that would make them very useful to the community.

require "CSV"
# make a movie lookup table
movies = Array.new
f = File.open('movie_titles.txt', 'r')
f.each_line do |line|
row = line.chomp.split(',', 3)
movies[ row.shift.to_i ] = row
end
f.close
# read all the ratings file and denormalize into one csv file
out = CSV::Writer.create(File.open(’ratings.txt’, ‘w’))
in_files = Dir[ "training_set/mv_*.txt" ]
in_files.each do |file|
f = File.open(file, ‘r’)
# first line is the movie id
movie_id = f.gets.to_i
rating = [ "", "", "", movie_id, movies[ movie_id ] ].flatten
printf “%5d - %s\n”, rating[ 3 ], rating[ 5 ]
f.each_line do |line|
rating[0..2] = line.chomp.split(’,')
out << rating
end
f.close
end