We have developed an application for managing digital assets which includes uploading of the assets, searching and workflow around these assets, we use RDBMS extensively for this. We now need to implment configurable attributes for these assets (instead of predefined ones which are managed via RDBMS) and keep all the existing functionality intact. What would be the best way to achieve this? is there an existing opensource framework for achieving things like this?
I also feel that the requirements are slightly vague, but I get a feeling that you may want to take a look at RESTful web services and HATEOAS (http://en.wikipedia.org/wiki/HATEOAS).
Here is a good article on how to implement workflows with RESTful web services: http://www.infoq.com/articles/webber-rest-workflow Frameworks that can do RESTful web services include JBoss RESTEasy, Apache CXF, Jersey (JAX-RS reference implementation) and Restlet.
Please do not hesitate to ask if there are additional questions!