Re: [xml] "Proper" way to use XML (not library specific)

[Yan Seiner <yan seiner com>]

Will Sappington wrote:
> I’m new to XML, but based on a recommendation and my own analysis 
> after the fact, XPath seemed a reasonable way to replicate this 
> functionality in XML because it allows you to directly access specific 
> elements. I’ve had some trouble implementing this, mostly due to a 
> lack of understanding of the library that was chosen (Xalan/Xerces). 
> In response to my troubles, my manager is saying that the problem is 
> with how I’m trying to use XML, not with the library. He says XPath is 
> not appropriate for this, that I should “marshal” the entire XML file 
> into a different form, toss the DOM, and operate on the transformed 
> data. I’ll put his email to me, edited for brevity, below. But my 
> question is, if XPath isn’t appropriate for this, then what is it 
> appropriate for? From the perspective of a configuration utility, it 
> certainly seems to be reasonable, if not obvious for the interface to 
> be such that the user can read specific configuration items from the 
> file in whatever order is desired, and XPath appears to be designed to 
> do specifically that with XML data. So why would it not be an 
> appropriate tool to use for migrating our existing name/value pairs 
> (.ini files) to XML?
>
> Many thanks in advance for any thoughts you might care to share.

I don't have anything technical to add to this, but I am very interested 
in this as well. My way of thinking is much like yours; I've written a 
handful of functions that pull attributes and values out of the DOM and 
use those; things like getElementValue and getAttribute.

A consultant we hired used your manager's method, converting the DOM to 
an array and then using the array elements.

I find my method easier to understand and maintain, but harder to 
program initially. The consultant's method is easy to program - he just 
has a single DOMtoArray function - but then has to test for the 
existence of each element separately, so his code ends up being full of 
if(isset(array['something'])) blocks.

Both methods work well from a performance standpoint. I think I will get 
some performance improvement by selecting a single method. I suspect 
that for large amounts of data handling the array method is quicker, but 
for pulling a small number of values out of the XML file my method is 
quicker. I haven't profiled this yet, though.

The XPath method is also more flexible, as it allows you to select a 
particular branch of the tree easily. I've broken up my single enormous 
config file ( 300K! talk about feature creep....) into a sequence of 
smaller files. Using XPath allowed me to do this very easily, whereas 
the array stuff is more-or-less hard-coded and harder to maintain.

--Yan