Abstract: Methods and systems are disclosed for storing, propagating, and searching for data stored in markup language documents, such as a data hierarchy defined by an XML schema. Each node in the data hierarchy may include an XML document representing an instance of the thing being categorized at that level of the hierarchy. A collection of such documents may be stored in a relational database according to a schema for storing the XML documents as well as the parent child relationships between the documents, i.e., a schema describing the data hierarchy. Further, a document at one node in the hierarchy may inherit attributes from its ancestors. That is, one node within a given hierarchy may inherit data from other nodes in the hierarchy as well as propagate information to descendants.