The MIX project (Mediation of Information using XML) is a collaboration between the UCSD Database Laboratory and the Data-intensive Computing Environments (DICE) group at SDSC. The goal of the project, which recently became a part of the I2T NSF Digital Government effort, is to study, develop, apply and evaluate systems for querying across heterogeneous information sources using XML. The focus of the technical development has been on the following issues:
Along this direction we developed in 1998 the XMAS query language for XML data. XMAS is a functional language, which is influenced by OQL and has a straightforward reduction to the tuple-oriented XMAS algebra. Its key difference from the XQuery core is that the tuple orientation is very visible to the user; in some XQuery implementations the tuple orientation is hidden from the user, yet it is used internally by the processor and enables query optimization in a fashion that is similar (but also different!) to what is known from relational, nested relational, and object-oriented databases. XMAS also has a group-by construct, which we hope will make it explicitly into XQuery syntax as well. At least, it is useful for internal optimization purposes.
Note that we do not expect conventional data repositories to be converted to XML. Such an approach would be unrealistic. Instead wrapping technologies allow us to logically view an information source (which may be a relational database, a collection of html pages, or even a legacy information system) as a large XML source. Wrappers are able to translate XMAS queries into queries or commands that the underlying source understands. They are also able to translate the result of the source into XML.
Furthermore, the Blended Browsing and Querying (BBQ) user interface enables the users to formulate XMAS queries using a GUI that reminds of query-by-example interfaces in relational databases.