Unraveling the duplicate-elimination problem in XML-to-SQL query translation

We consider the scenario where existing relational data is exported as XML. In this context, we look at the problem of translating XML queries into SQL. XML query languages have two different notions of duplicates: node-identity based and value-based. Path expression queries have an implicit node-identity based duplicate elimination built into them. On the other hand, SQL only supports value-based duplicate elimination. In this paper, using a simple path expression query we illustrate the problems that arise when we attempt to simulate the node-identity based duplicate elimination using value-based duplicate elimination in the SQL queries. We show how a general solution for this problem covering the class of views considered in published literature requires a fairly complex mechanism.