The first version of this page was written in 1999 and since then it has been revised at a few points.

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:

We first describe mediation based on distributed XML queries and then the particular contributions of MIX.

What is a Mediator and Why it is Needed?

The information accessible thru the Internet is a tremendous asset to the users who will be able to find and combine the data related to their problem. This is not an easy task since the information is distributed across many sources, each source provides a different interface and exports the data in a different format. Mediator systems will assist the users by providing to them integrated views of the data they are interested in. For example, a Web-shopping mediator will provide to the Web value-shopper a view where the lowest prices for each product are provided.

The Philosophy of MIX: The Web as a Distributed Database

We strongly believe that the Web emerges as a distributed database and XML as the data model of this huge database. In the near future sources will be exporting an XML view of their data along with semantic descriptions of the content and descriptions of the interfaces (XML queries) that may be used for accessing the data. Users and applications will then be able to query these view documents using an XML query language.

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.


MIX Resources