Computing Compressed XML Data from Relational Databases

SQL/XML allows generating an XML document as the result of a query that is evaluated on relational data. This facilitates companies sharing their relational data in form of XML documents with other companies or with a marketplace, but significantly increases the exchanged data volume. To reduce both the volume of the exchanged data by exchanging compressed XML and the time needed for compression, we propose an approach that allows preparation of a compressed XML document as the answer to an SQL/XML query directly, i.e., without the need to create the XML document first and compress it afterwards. Our evaluation has shown that generating the compressed document directly is in most cases faster than generating the uncompressed XML document and compressing it, and in some cases it is even faster than the generation of the uncompressed XML document alone. As our approach of generating compressed XML requires only SQL support from the underlying database system, a second advantage is that it can be used for the generation of compressed XML even for database systems that do not (yet) support SQL/XML (like MySQL).