Workshop 2 - SimpleXML in PHP

Using the xpath function in SimpleXML in PHP is a bit tricky, so here is how to do the decoding:

Create an XML file like this. called bbcCodes.xml

and these PHP statements do the lookup:

$name = $_REQUEST["name"];

$places = simplexml_load_file("bbcCodes.xml");

$codes = $places->xpath("//Place[name='$name']/code");

print $codes[0];

Here it is running -

This PHP script uses the xpath function which returns an array of SimpleXMLElements (since this match will usually produce a sequence of elements) so you need to pick out the first one (assuming there is only one match)

Lecture week 14 - XML and XPath

In this lecture I will discuss character encoding, an issue which arose form the workshop last week. It turns out that the essential problem here is the same as the problem which namespaces try to solve - how to mix data from multiple sources (here in multiple languages).

Then we do a bit of revision on XML structures and well-formedness, introducing the XML diagrammer in QSEE.

Then I look at the basics of XPath, a language for selecting parts of a XML document.

This leads into the continuation of last week's worksheet, extending the PHP script with the means to enter a place name and get the formatted forecast for that area.

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Workshop 2 - continuing with the weather feed.

Last week you wrote a PHP script using SimpleXML to fetch an RSS feed from the BBC and formatted a page to display the forecast which was embedded in the RSS.

You noted that the way detailed weather data was handled by the three feeds (The Weather Channel, BBC and Yahoo) were very different and illustrate the point that merely using XML doesn't solve problems of communicating complex data. We also encountered problems with namespaces and attributes with the Yahoo feed. However the worksheet is about the BBC feed so we will avoid this problem for the moment.

In the last part of the work sheet, it asks you to parameterise the script so it can be used for different locations, identified by name This is a problem because the feeds are identified by an id internal to the BBC.

To solve this problem you can add your own data file which contains pairs of Place names and the corresponding BBC code. This data could be held in any of several forms - as a simple text file, as a MYSQL table but for this part of the course, you will create a small XML file to hold these pairs and then use a bit of XPath to find the matching record.

We will cover the basics of XPath in the lecture and how it is used in SimpleXML.

Next week we will be looking at creating more complex XML - kml files to create overlays for Google Earth. In preparation, please take a look at the introduction to GoogleEarth in this blog.