Today while was trying to make a custom control to convert currencies, I faced an ugly problem: The free soap web service that I was planning to use was simply down. A big problem considering the time I had to made that control.
After some goggling I found some sites that perform this kind of job. Some of them were using originally the same web service I was trying to use and because they were facing the same problem as me they decide to change it. They were using somehow the YAHOO finance quotes service to retrieve the exchange rate between two currencies, but they were making the calls directly at the server side (trying to do it using Ajax raises the Cross Site Scripting problem).
Then I was curious about to know if somehow the YAHOO finance service could had some kind of REST API that could help me to obtain this value directly. But I was not lucky and couldn’t find that…
The YQL stands for Yahoo! Query Language. This is a really impressive concept. It basically allows to make calls to almost any web resource (html pages, dynamic pages and any other resource) and query this result using css or xpath to retrieve the parts of the content that are relevant for us in JSON or XML formats. And it supports make Cross Site Scripting calls too!
The potential that I found in this tool is really amazing you can retrieve almost any relevant information from many sites and use it in the way you want.
YAHOO has some good resources. Really good resources!