A heterogeneous data integration system can integrate a broad range of data sources including WWW.Decomposition and optimization for query are very difficult because some data sources have neither regular schemata nor strong query capabilities.To help query decomposition and optimization,a dynamic dictionary is proposed as unified schemata for various heterogeneous data sources,and the way for the construction of a global dynamic dictionary by operating on dynamic dictionaries of local data sources is given.Furthermore,to simplify the design of wrappers for data sources with limited capabilities and reduce responding time for query,an approach,which can take advantage of all powers of various data sources and results of prior queries,is proposed for query decomposition and optimization.