Keys with Upward Wildcards for

The paper proposes a key constraint language for XML and investigates its associated decision problems. The language is deened in terms of regular path expressions extended with downward and upward wildcards, which can not only move down XML document trees, but also upwards as well. In a uniform syntax it is capable of expressing both absolute keys and relative keys, which are important for hierarchically structured data, including but not limited to XML documents. In addition to being expressive, keys deened in the language can be reasoned about eeciently. In particular, the paper provides a sound and complete set of inference rules and a cubic time algorithm for determining ((nite) implication of these key constraints.