Web based online diagramming (how are those software implemented)

Could someone guide me on how web based online diagramming software's work? I would really appreciate if you could point me to example resources to get some knowledge on this.

Following are the some of the samples web based online tools that iIhave been trying to studying:

http://www.creatly.com

http://smoot.sourceforge.net/smoot/

This second example has source cod开发者_如何学运维e for the implementation as well. But if any of you have prior experience on this subject, could you share it with us?

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Take a look at Yahoo! Pipes source. It uses <canvas> and it looks great! And if you need a library to help you - take a look at Raphael and its special graph plugin gRaphael.

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I haven't heard of diagrams being drawn clint side though I suppose it's possible using activex-software, flash or some type of module that the user installs on his/her browser. The most common is to use server-side software to generate images. My experience in this area comes from PHP and from the image generating libraries there. You can draw pretty much anything. I've also come across packages like, Image_graph, free and open source, specifically aimed at diagrams.