1. Query Relaxation for XML Database Award #: 0219442 PI: Wesley W. Chu Computer Science Dept. UCLA

2. Problem Overview Goal –Develop an XML query relaxation framework for searching answers that can approximately match the given query conditions. Query Relaxation –Relax the query constraints to derive approximate answers if the original query returns no answer or not enough answers. Relaxation types –Value relaxation: expanding the value constraints in the query –Structure relaxation Node relaxation: node re-label, node deletion Edge relaxation: generalizing parent-child edge “/” to ancestor-descendant edge “//”.

3. X-TAH: Knowledge-based Relaxation Index X-TAH: –Generated by clustering similar XML fragments into hierarchical tree-like structure based on inter- object distance and inter- cluster distance. Relaxation with X-TAH –Generalization –Specification An example of X-TAH Q XML fragment Cluster Representative

4. System Overview Satisfactory Answer Postprocess Module Yes Present Answers Approximate Answers Query Processing XML Query Select Condition to Relax No X-TAH Query Relaxation

5. System Overview