Friday, February 18, 2005

Comparing YARS and Kowari

Cold, Mastering OWL, Scalability, Indexing "There are two differences in their implementation to our own. The first is that they used B-trees rather than the AVL trees that Kowari uses. That is not a significant difference, and I blogged about this several times before. The main advantage of the AVL tree is that they are cheaper to write to the structure than B-trees are, though a little slower to read. They also pointed out that they wanted to use an existing library for the index, and while B-tree libraries are common, we never found a completely working AVL tree library (deletions were always buggy).

The second difference is a set of special statements which count the number of triples in parts of each of the indexes. This is certainly novel, but not an approach I would use. I believe that counting is still very efficient in Kowari (O(log(n)), and the space overhead they incurred would seem prohibitive. More importantly, writing is always the slowest operation, and their system would incur a large writing penalty for using this scheme."
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