With the availability of large treebanks, retrieval techniques for highly structured data now become essential. In this contribution, we investigate the efficient retrieval of MT structures at the cost of a complex index--the Treegram Index. We illustrate our approach with the VENONA retrieval system, which handles the BH t (Biblia Hebraica transeripta) treebank comprising 508,650 phrase structure trees with maximum degree eight and maximum height 17, containing altogether million Old-Hebrew words. 1 Multiway-tree retrieval based on treegrams To cope with this tree-retrieval problem, we generalize the well-known n-gram indexing technique for text databases: In place of substrings.
