Extracting Data

Hi... I am relatively new to programming and I will appreciate all the help I can get from this community to understand how some things work.

My question is, how can I extract product specific data (image, price, features, discounts, etc. ) from online shopping sites (Yahoo!Shopping, Walmart, Sears, etc.) and display them on a different website. Also, is this process legal and is there a need to get prior permission from these shopping sites?

I am talking of something on lines of the 'Facebook like button' seen on many product pages, which when clicked extracts the product data from Yahoo!Shooping site and displays it on Facebook.

Please help!
Shashi.

This is referred to as screen scraping or web scraping. You can find a general bit of information about it here: http://en.wikipedia.org/wiki/Web_scraping.

I am NOT a lawyer, so I will refrain from commenting on the legality. There is some information on the Wikipedia page about it and it appears to largely be unsettled law. This is not legal advice. Consult someone knowledgeable before deploying any system to production.