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Check the Facts and PL/SQL Code
This technique is commonly referred to as 'Name-Value pairs', and is used successfully on a commercial scale.
For example, by SalesForce.com to support a global community of
many thousands of Users and to provide User-Defined Attributes.
SalesForce uses Java and once the appropriate Code Libraries are in place, then this approach scales well and can be used
to provide 'industrial-strength' performance and reliability.
Some details are shown on my Data Model for SalesForce.
You can also sign on for a free Trial of SalesForce, and check out their Developers platform at Sforce.com.