The EAV model is as everything else a tool. Used correctly, though it rarely is, is extremely powerful. The Relational model when implemented to address a specific problem is quick, robust and maintainable. Can they be used together ? Sure... but there are boundries that if crossed. will bring a project to it's knees. Sure storing data in 'skinny' structures is easy but the implementation of an application to manange, modify and view that data is complex and error prone. But one can't deny the ability to store vast amount of data in a single table. SQL Server 2008 and on employ Spare tables to help address the storage of tables with large numbers of columns and no data but, they to, have limitations. For example range check constraints are not possible (though Data types are). So whatever the solution you are after be aware of the design considerations required to achieve your aims.

COde On:-P