Java Platform Any Good?

[eek]

Now to figure out the database...which might end up being one of these NoSQL jobs as the data is highly conceptual with almost everything having attributes and yet also being located somewhere is a user-defined hierarchy. fun.

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Been there done that. It's a multi tier hierarchy you will need then. One to store their user defined bits and another to contain the actual data.

No SQL doesn't really solve the user defined problem. You still (somehow) need to index the fields they navigate through