Need Technology Recommendation: Web-based Database Manager

I'd like to build a proof-of-concept web-based database manager (such as the desktop version in the screenshot below) that has the following features.

The schema will be provided initially through a flat file.

It seems like HTML5 might be an option. What about non-HTML? What about processing.js? Are there any libraries I could/should take advantage? Is there already a service I can tap into?

Any opinions or advice would be appreciated!

Edit Primary goal of the project is the build a protoype of the UI.

For the events that you will need to control everything, I would suggest using jQuery. It can cut you javascript in half. Canvas/SVG would be easy enough to use to create the diagram above (could even pull it off in straight html using some creative css and a judicious application of div's). I've never used flash but I also don't see anything in your image here that couldn't be done in Canvas/SVG. If you do go with Canvas you will want to look into using a lib called ex_canvas which will make it all work fairly nicely on IE (my company has some canvas items that work in IE6 using ex_canvas). Also you will want to look at css-sprites (in case you haven't heard of them before) as they can aid in the load performance of your page.

I've decided to use http://raphaeljs.com for the project. This SVG library supports older browsers and given this application is highly interactive with the user, it makes sense for me in this project to use SVG over Canvas.