pg_xnode is an extension (module) which adds several data types to the PostgreSQL database server, allowing it to store XML documents, XML (tree) nodes, and XPath expressions. Unlike the in-core implementation of XML, pg_xnode does not require repeated parsing of XML data, and thus should be more efficient. In addition, the extension has functions to add/remove nodes to/from existing XML documents, and templates to create XML documents from tables.
RecDB is a recommendation engine built entirely inside PostgreSQL 9.2. It allows application developers to build recommendation applications using a wide variety of built-in recommendation algorithms such as user-user collaborative filtering, item-item collaborative filtering, and singular value decomposition. Applications powered by RecDB can produce online and flexible personalized recommendations to end-users. It is easily used and configured and allows novice developers to define a variety of recommenders that fits their application's needs in few lines of SQL. It can seamlessly integrate recommendation functionality with traditional database operations.