  In contrast to XML query languages as e.g. XPath which require knowledge on
the query language as well as on the document structure, keyword search is open
to anybody. As the size of XML sources grows rapidly, the need for efficient
search indices on XML data that support keyword search increases. In this
paper, we present an approach of XML keyword search which is based on the DAG
of the XML data, where repeated substructures are considered only once, and
therefore, have to be searched only once. As our performance evaluation shows,
this DAG-based extension of the set intersection search algorithm[1], [2], can
lead to search times that are on large documents more than twice as fast as the
search times of the XML-based approach. Additionally, we utilize a smaller
index, i.e., we consume less main memory to compute the results.
