Querying markup language data sources using a relational query processor

A computer-readable medium of instructions for execution by a computer and suitable for specifying a mapping of a plurality of nodes contained in a mark-up language document according to a relational schema into a plurality of tables, comprising:

• first program instructions for creating a first table based on a first type of node from the document, the first instructions including an option specifying a location within the mark-up language document of the first type of node;
• and
• second program instructions for creating a second table based on a second type of node from the document, the second type of node related to the first type of node, and the second program instructions including an option specifying a location within the mark-up language document of the second type of node.

A method of locating a path from a descendent node to a root node in a document containing hierarchical information, the method comprising joining a table holding information of the descendent node and a table holding information of the root node, wherein each of the tables has a primary key and a foreign key, columns of the table holding the descendent node information are selected, and predicates for the join are taken over the primary and foreign keys of the selected tables.

A computer based system for querying a markup language document having hierarchical information including a parent node and descendent nodes related to the parent node, comprising:

• a data source having stored therein a markup language document;
• a wrapper unit configured to extract information from the markup language document in response to a query by consulting a mapping specification containing information for locating the parent node, and if the parent node satisfies the query to store the parent node in a first table, and to locate the descendent nodes by consulting the mapping specification if the parent node satisfies the query and store said descendent nodes in a second table.