ECST – Extended Context-Free Straight-Line Tree Grammars

Abstract

Abstract. Grammar-based compressors like e.g. CluX [1], BPLEX [2], TreeRePAIR [3] transform an XML tree X into a context-free straight-line linear tree (CSLT) grammar G and yield strong compression ratios compared to other classes of XML-specific compressors. However, CSLT grammars have the disadvantage that simulating on G update operations like inserting, deleting, or re-labeling a node V of X requires to isolate the path from X's root to V from all the paths represented by G. Usually, this leads to an increased redundancy within G, as grammar rules are copied and modified, but the original and the modified grammar rules often differ only slightly. In this paper, we propose extended context-free straight-line tree (ECST) grammars that allow reducing the redundancy created by path isolation. Furthermore, we show how to query and how to update ECST compressed grammars.

Direct Update of XML Documents with Data Values Compressed by Tree Grammars

“…[5] proposed a parallelization of path isolation in updating grammars. [2] further optimized an updating algorithm by representing queries by DAGs and [6] proposed an extension of SLCFTG so that redundancies appearing in path isolation can be reduced. In [7], a recompression method is proposed such that tree digrams across more than one rules are searched in an SLCFTG updated by path isolation, and the detected digrams are locally compressed by TreeRePair.…”