BBC Weather forecast

keywords: RSS, PHP, SimpleXML, BBC weather

Background to RSS

The data from the weather channel was provided in a format which was specific to this source. If data is being combined form several sources, it may be better to have one common format. One such format (or family of formats) is called RSS – which could stand fro Real Simple Syndication. RSS is an XML format for news items. There are a number of different standards used (RSS 0.92, RSS 2.0, Atom) so writing a general reader for RSS is difficult. However for a single feed, with a known format, this is rather straightforward to do with PHP and the SimpleXML functions.

The BBC provides a wide range of RSS feeds. Amongst them are feeds of weather forecasts. They are listed on this page which also explains the background to RSS.

http://news.bbc.co.uk/1/hi/help/rss/3223484.stm

Exercises

Exercise 1 BBC Weather feeds

Starting at http://www.bbc.co.uk/weather/ locate the page for Bristol (There are actually two pages perhaps for different airports)

Note that there is the sign for an RSS feed on the page – an Orange rounded rectangle. Click on this link.

( it should be http://feeds.bbc.co.uk/weather/feeds/rss/5day/id/1263.xml )

where the BBC has coded Bristol as '1263' (or 1269)

To see the raw XML, view source. A listing of a similar file is show in Appendix 1. This feed, as you can see from the rss tag, is in RSS 2.0 format.

The browser displays the file in a readable format. This is because of the link to an xsl stylesheet in the xml-stylesheet directive (the second line). You can see the stylesheet itself if you browse the link to it. We will be doing more on XSLT later in the term.

Q: How could you change the stylesheet to one of your own?

A: Not sure if this is possible.

Exercise 2

Save the xml file, open it in a text editor like PFE32, remove the xsl directive and display this modified file in a browser. Note that without the stylesheet, the browser displays the file as a foldable hierarchy.

Note which items are XML attributes and which elements. What is ° ?

In this example there is only one item in the feed but normally there are many.

Exercise 3

Write a PHP script to display the forecast in a format suitable for display on the Foyer monitors. A simple script can just show the text, a more complex task is to show the different data items separately, perhaps graphically.

Hint - use the example of the extraction of data from The Weather Channel site. You will have to use the function to read a file via the proxy here if you run this on a CEMS server.

Q. How can the individual data items in the BBC feed be extracted?

A. You can use Regular Expressions to match text around the value of interest – see Patterns, in Wikipedia and in PHP ereg() function. This technique, particularly when it is applied to a whole HTML page, is called 'screen scraping'

Exercise 4

Yahoo also provide a weather feed – for example:

http://xml.weather.yahoo.com/forecastrss?p=UKXX0025

which is described in their developer page:

http://developer.yahoo.com/weather

In this RSS feed, the weather data itself is included using another namespace. Note that these prefixes are just local names - the URIs are the global unique identifiers

For the geo namespace - http://www.w3.org/2003/01/geo/wgs84_pos#

For the yweather namespace - http://xml.weather.yahoo.com/ns/rss/1.0

Compare the data in these two feeds and that from the Weather Channel .

Q. What differences do you see between the XML representations of weather data in these three sources? Which is most useful for later processing?

Q: What differences and similarities to you see in the data itself? Can you explain this?

Exercise 5

Generalise your script to allow different locations to be displayed, and use this to display your own home town or other place of interest in the UK.

Q. How do I find the code for this town?

A. Go to the BBC Weather site at http://www.bbc.co.uk/weather/ and search for the town or postcode. You may have to resolve any ambiguity on the disambiguation page (often airports appear separately to the city). On the forecast page itself, note the number in the URL - id=nnnn. [There has to be a better way to do this !]

Q how to I create the XML file

A. Use any text editor – design the file to use only text elements, not attributes – its simpler

Q How do I use XPath in PHP?

A 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)

Exercise 6

Display the location of the place: Note that the location data is in a different namespace with a prefix geo.

To access the location data, you need to understand how SimpleXML treats namespaces. See Elliotte's article and Mark's script which shows how namespaces can be registered and used in XPath expressions

In a later exercise we will use this data to create an overlay for GoogleEarth and Google Maps.

References

RSS

Help from the BBC http://www.bbc.co.uk/feedfactory/help_what.shtml

Wikipedia

My Web2.0 wiki

Elliotte Rusty Harold on SimpleXML : http://www-128.ibm.com/developerworks/library/x-simplexml.html

Yahoo Developer Page

Appendix 1

This is the RSS feed for the Bristol forecast on Christmas Eve (!).:

<?xml version="1.0" encoding="UTF-8"?>

<?xml-stylesheet type="text/xsl" href="http://feeds.bbc.co.uk/weather/feeds/rss/5day/weather.xsl"?>

<title>BBC - Weather Centre - Forecast for Bristol (BS1), United Kingdom</title>

<description>by the BBC Weather Centre in association with the Met Office</description>

<copyright>Copyright: (C) British Broadcasting Corporation</copyright>

<managingEditor>weather@bbc.co.uk</managingEditor>

<webMaster>weather@bbc.co.uk</webMaster>

<item>

<title>The forecast for Bristol (BS1), United Kingdom on Sunday: cloudy. Max Temp: 4°C (39°F), Min Temp: 4°C (39°F), Wind Direction: NE, Wind Speed: 3mph</title>

<description>The forecast for Bristol (BS1), United Kingdom on Sunday: cloudy. Max Temp: 4°C (39°F), Min Temp: 4°C (39°F), Wind Direction: NE, Wind Speed: 3mph, Visibility: moderate, Pressure: 1039mb, Humidity: 86%, UV risk: low, Pollution: moderate, Sunrise: 08:14GMT, Sunset: 16:04GMT</description>

<guid isPermaLink="false">tag:feeds.bbc.co.uk,2006-12-23:/weather/5day/id/1263</guid>

<geo:lat>51.45</geo:lat>

<geo:long>-2.60</geo:long>

</item>

</channel>

</rss>