Abstract: The index of XML Data is crucial for retrieval efficiency of XML document After analysis of existing XML structure summaries, this paper proposed a structural summary over keyword search called LSS combining the XML document. I_SS merges the nodes in the XMI_ tree with the same label path so as to determine nodes' homogeneity and heterogeneity efficiently. This paper implemented LSS constructing algorithm called CSCAN, and designed a XML keyword retrieval algorithm called LSScarch based on LSS. hhis algorithm split keywords' inverted list into different type subsets,finally retrieved to get all results quickly on these subsets. Experimental results demonstrated that I_SS can help to reduce the size of the keyword inverted list in XML document dramatically and improve retrieval efficiency.

Key words: XML，Keyword search, Indices, Inverted list