A URL producer/consumer contract
Before we start, a word of apology to geek terminology pedants. Yes, I know that I should really be using the acronym 'URI' rather than the acronym 'URL' in the title of this article but hey, I am human too. I have also been known to use the word 'Hoover' when I really mean 'vacuum cleaner'. I sometimes say 'hard disk' when I should really say 'USB key'...I could go on with more examples and I am sure you could too.
The fact is, I regularly say 'URL' in conversation when I really mean 'URI'. To be sloppy with words is to be human. My field tests have shown that normal living breathing people - whether we like it or not - have internalized the term 'URL' to an incredible degree. The term 'URI', quite frankly, does not occur too often outside of inner geek circles. Terminological correctness aside, the real world is such that the term 'URL' prevails. We pedants just have to live with that fact. When I say 'URL', hereinafter, please feel free to substitute 'URI'...
The great thing about URLs is that you can click on them. One of the most awesome, inaudible rumbles emanating from our planet in this twenty first century, is the constant clickity-hum of a billion mouse clicks created by browser wielding people. Many of these clicks on URLs will just work. However, a not insignificant number will result in a banging noise like this:
'Thank you for your visit, cherished visitor. The page you are looking for does not appear to be available any more. Please contact our administrator or try again later.'
The fact that URL links can fail to work is one of the fundamental features of the approach to hypertext taken in the World Wide Web. There are other approaches of course. Approaches that would ensure that links would never, ever break. However, they all come at very significant extra cost in terms of complexity. On this issue, the world has voted very loudly with its mouse clicking fingers. The world values hyperlinking simplicity over complexity by many orders of magnitude.
Having said that, links that break are a real pain. When visiting a web site, I often come across interesting pages and say to myself 'I want to bookmark this for later'. Then as I load up del.icio.us or my local WIKI pages, I find myself thinking 'Gee. I wonder if this link will work the next time I click on it?'.
Unfortunately, there is no simple way to get an answer to this question. Links on the Web can break. That is the way the Web works...
Okay. I understand that. But here is what I am thinking: what if, producers of URLs could somehow indicate that a URL is going to work for a long time? That would allow bookmarkers like me to make an informed judgment about the permanence or otherwise of the URLs I come across. I am not talking about any heavy technology to make this work. I am thinking of nothing more complicated than a social naming convention. What if permanent URLs contained the fragment '/purl/' for example? Would that not do the trick? As a consumer, I look at example.com/purl/info12.html and can immediately infer that it is a good candidate for bookmarking.
From a URL consumer's perspective, this would be very handy I think. From a URL producer's perspective, it would also be very handy. In effect, it would allow URL producers to send out signals to the world. One signal would be: 'this URL is a good bookmark candidate. We won't be changing it and even if we change our systems internally, we will make every effort to ensure that this link will continue to work.'. The second signal would be 'This URL is not a good bookmark candidate. Bookmark it at your own risk.' Simply leaving '/purl/' out of a URL would send the latter signal.
This seems to me to be an effective, low tech way of getting to a middle ground in which, although links can break, links can send out signals to potential consumers so that breakages can be anticipated by consumers in advance.
Some pedants are no doubt observing that the term 'puri' is more correct than the term 'purl'. Pedants that are also fans of Indian food are also salivating at this point [1].
Whatever you want to call them, puris or purls would be links that you can click on with confidence and bookmark with confidence. They would not change and would therefore be cool in Tim Berners-Lee's eyes [2]. To paraphrase Sir Berners-Lee: cool PURLs don't change.
[1] http://www.currypages.com/dishglossary.aspx?dish=Prawn+Puri
[2] http://www.w3.org/Provider/Style/URI