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DNS Structure: Introduction

Part 2

Along Comes the Web

Then, in the 1990s, the World Wide Web exploded onto the scene. Beginning in 1990 as a system at European physics laboratory CERN to allow researchers in high-energy physics to share information, the Web started slowly (and for a few years trailed the menu-based Gopher system as the leading system for structured online information), but started a massive growth in popularity once the graphical browser Mosaic came out in late 1992. First it was used by people who already had access to Internet-connected computers, mostly college students, but then the mass media started noticing it, and this fueled a demand for commercial Internet providers, which started springing up in early 1995. Also, the online services like Prodigy, CompuServe, and AOL added Web browsers to their software, so suddenly a mass audience from outside the traditional "geek" circles was using the Web.

The Incredible Shrinking URL

When the masses first flooded onto the Web, most of the sites they browsed were still on academic servers, since few commercial web hosting providers existed. URLs tended to be long, technical things, like:

http://unix4.complab.cs.somewhere.edu:8080/~jsmith/pub/docs/html/homepage/homepage.html

Immediately, people involved in developing for the Web started working to shorten and simplify this. Most of these simplifications made a good deal of sense, removing unnecessary complexities from the structure of URLs. However, in hindsight, maybe it would have been better if they hadn't done this, since this produced a drive to keep simplifying things even to the point of eroding some of the useful structures -- once people got used to URLs sometimes being short and simple and un-techie-ish, the developers of Web sites wanted all of their URLs to be that way, and didn't mind abusing the domain name system to do this.

To see how this progression occurred, look at the above URL and note the ":8080" -- this is a port number. Web developers quickly realized that if they put all Web servers in the default port, 80, they could omit that portion of the URL, shortening it to:

http://unix4.complab.cs.somewhere.edu/~jsmith/pub/docs/html/homepage/homepage.html

Then, by learning to use default index files so that they could give a directory name alone without a filename after it, they can shorten it to:

http://unix4.complab.cs.somewhere.edu/~jsmith/pub/docs/html/homepage/

Next, they could make sure that their main home page was in the directory the server pointed at, rather than more deeply nested in a directory structure that was designed when the Web was only one of many uses for the computer the server was on; this cuts a few subdirectory names out of the URL:

http://unix4.complab.cs.somewhere.edu/~jsmith/

If "J. Smith" was just an ordinary user of that computer, this might be the furthest he could go at simplifying his URL, but if he were the system administrator, he might move his homepage to the server root and cut out the need for a "tilde" and username:

http://unix4.complab.cs.somewhere.edu/

Now we're getting somewhere. At this point, the sysadmin may realize that the URL would get even simpler if he could create an aliased name in his department's DNS (domain name service) -- instead of just using the hostname of the machine the server happens to be running on, he can create the hostname "www" and make it equivalent to it. This lets the URL become:

http://www.cs.somewhere.edu/

Enough administrators did this that it rapidly became the "standard" for Web addresses, and soon hardly any of them were on hostnames that didn't begin with www. (In the long run, though, this proved to be a transitional stage; the trend these days is to drop the www and use the "naked" domain name with no hostname preceding it. This would have been unthinkable just a few years ago, while the Web was just one of many different services being used on Internet-connected machines, and didn't yet have the enormous prominence it now does -- administrators wouldn't have wanted to tie up the root domain of their site by aliasing it to their Web server in preference to the servers for all other services such as FTP or Gopher.)

At the same time, browsers were being made more intelligent at completing URLs that were missing some parts, since they could fill in the most common values themselves. In particular, the http:// part could be inferred. Also, people could get away with omitting trailing slashes (though in some cases this produces a wasteful extra server redirect). Thus, though it wasn't technically speaking a proper URL, people got used to addressing the above site as:

www.cs.somewhere.edu

But by this time, .edu sites like this were becoming a minority compared to commercial sites, which were sprouting up at a rapid pace. Unlike the university sites, which were usually grouped by department in a hierarchical structure, the commercial sites were usually designed to promote the company and its products in a unified manner, and thus had addresses of the form www.companyname.com, not needing subdomains for departments and divisions, as these didn't usually have separate Web sites. Thus, it came about that the public expected Web addresses to be of the form www.something.com (or just something.com, as the www part became increasingly considered optional).

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