Database Reference
In-Depth Information
Chapter 9
Pattern-Based Schema
Mapping and Query Answering
in Peer-to-Peer XML Data
Integration System
Tadeusz Pankowski
Poznan University of Technology, Poland
ABSTRACT
This chapter addresses the problem of data integration in a P2P environment, where each peer stores
schema of its local data, mappings between the schemas, and some schema constraints. The goal of
the integration is to answer queries formulated against a chosen peer. The answer must consist of data
stored in the queried peer as well as data of its direct and indirect partners. The chapter focuses on
defining and using mappings, schema constraints, query propagation across the P2P system, and query
answering in such scenario. Schemas, mappings, constraints (functional dependencies) and queries
are all expressed using a unified approach based on tree-pattern formulas. The chapter discusses how
functional dependencies can be exploited to increase information content of answers (by discovering
missing values) and to control merging operations and propagation strategies. The chapter proposes
algorithms for translating high-level specifications of mappings and queries into XQuery programs, and
it shows how the discussed method has been implemented in SixP2P (or 6P2P) system.
