One of the most excellent aspects of HTTP and the underpinning REST architecture is the aspect of idempotence and non-idempotence. Idempotence roughly means that some operation yields the same result whether it is done only once or several times. This behaviour forms the basis of caching because if the result is the same you can work with a copy of the result for all subsequent requests. This excellent property of the web also has some downsides as the Law of Preservation of Complexity demands that for any goodness in technology there always is a trade off in increased complexity somewhere else. In the case of caching it is determining when to cache and when not to cache.
Archive for the ‘Featured’ Category
October2
Lies, damned lies and caching
My work for the Lilliput CMS has lead to some interesting new findings about PHP 5′s new DOM functions, particularly the XPath part of it. Whilst working on the templating structure for Lilliput I couldn’t get the DOM XPath queries to work on the file at hand, a normal XHTML 1.0 Strict document. With an external tool called XPath Explorer (XPE) every query evaluated correctly but as soon as I tried the same XPath expression in PHP it failed. After searching long and hard I came across a code snippet that contained the solution namely to explicitly declare the xhtml namespace for the DOM document you’re working on:
October2
Building the previous blog
This blog uses used a novel approach (I think) in that it is was entirely Atom 1.0 based. There is was no underlying (X)HTML, everything is was Atom (with a hint of XSL). I came to this approach after I figured out that it is silly to serve the same content in multiple formats when one format suffices. Modern browser are perfectly capable of executing XML/XSL that allow for the transformation of the Atom 1.0 feed into XHTML. There’s some nice stuff going, let’s dig into the details (hey I’m a technologist at heart so why not busy myself with the stuff I love).