Foreign-Key Based XPath Navigation

XML Schema defines identity constraints, including key and foreign key constraints. We consider the problem of navigating from a keyed element to its referring ”children” and, conversely, from an element containing a foreign key to the ”parent” it references. Our contributions are as follows. We extend an expressive fragment of XPath, called XPath′, with navigation axes according to foreign keys, resulting in a fragment called XPath′fk. We show a polynomial time algorithm for the evaluation of XPath′fk queries. We prove that XPath ′ fk is strictly more expressive than XPath′. Finally, we show that under certain conditions, if keys are restricted to have only one field then XPath′fk is equivalent to XPath′.