1. A computer program product for XPath evaluation in an XML data repository, comprising: a non-transitory computer readable storage medium having program instructions embodied therewith, the program instructions executable by a processor to cause the processor to: generate a simple path file comprising an XML file by merging nodes of hierarchical architectures of a plurality of XML files in the data repository to form a hierarchical architecture, the simple path file including a tree-like structure for the hierarchical architecture comprising nodes corresponding to storage blocks in the data repository that store data from the plurality of XML files, each of at least one node in the hierarchical architecture of the simple path file corresponding to a plurality of nodes with at least two of the plurality of nodes from different ones of the plurality of XML files, and node names of nodes in the generated XML file are generated by recording tag information of respective nodes in the plurality of XML files in the data repository; store data in the data repository in an orderly manner according to each node in the hierarchical architecture of the simple path file; parse an input XPath query by applying the XPath query to the hierarchical architecture of the simple path file to generate an execution tree for the XPath query, wherein the execution tree includes a tree-like structure with nodes including identifiers referencing nodes in the hierarchical architecture of the simple path file for obtaining data; and execute the execution tree for the data repository to generate a final evaluation result by retrieving data of the plurality of XML files from the storage blocks in the data repository corresponding to the nodes of the hierarchical architecture of the simple path file referenced by the execution tree and combining the retrieved data to produce the final evaluation result.
2. The computer program product according to claim 1 , wherein the simple path file is updated by XML files added into the data repository.