S2CX: From relational data via SQL/XML to (Un-)Compressed XML

• SQL/XML query evaluation generating compressed and non-compressed XML formats.
• Supports SQL/XML on all relational databases, even those not supporting SQL/XML.
• Generates directly compressed XML formats without need to generate XML format first.
• In most cases, our approach outperforms SQL/XML query evaluation of DB2 and Oracle.
• Our approach scales better than SQL/XML query evaluation of DB2 and of Oracle.

The gap between storing data in relational databases and transferring data in form of XML has been closed e.g. by SQL/XML queries that generate XML data out of relational data sources. However, only few relational database systems support the evaluation of SQL/XML queries. And even in those systems supporting SQL/XML, the evaluation of such queries is quite slow compared to the evaluation of SQL queries. In this paper, we present S2CX, an approach that allows to efficiently evaluate SQL/XML queries on any relational database system, no matter whether it supports SQL/XML or not. As a result to an SQL/XML query, S2CX supports different output formats ranging from plain XML to different compressed XML representations including a succinct encoding of XML data, schema-aware compressed XML to grammar compressed XML. In many cases, S2CX produces compressed XML as a result to an SQL/XML query even faster than the evaluation of SQL/XML queries into non-compressed XML as provided by Oracle 11 g and by DB2. Furthermore, our approach to query evaluation scales better, i.e., the larger the dataset, the faster is our approach compared to SQL/XML query evaluation in Oracle 11 g and in DB2.