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Combining Pat-Trees and Signature Files for Query Evaluation in Document Databases

Summary: Combining Pat-Trees and Signature Files for
Query Evaluation in Document Databases
Yangjun Chen and Karl Aberer
IPSI Institute, GMD GmbH, Dolivostr. 15,
64293 Darmstadt, Germany
Abstract. In this paper, a new indexing technique to support the query evaluation
in document databases is proposed. The key idea of the method is the combina-
tion of the technique of pat-trees with signature files. While the signature files are
built to expedite the traversal of object hierarchies, the pat-trees are constructed
to speed up both the signature file searching and the text scanning. In this way,
high performance can be achieved.
1 Introduction
We consider the combination of two different indexing techniques: signature files and
pat-trees for optimizing query evaluation in document databases. Signature files can be
feasibly organized into a hierarchical structure and therefore suitable for indexing doc-
uments stored structurally (in an object-oriented database). Concretely, it can be used to
speed up the traversal along object hierarchies by filtering non-relevant objects as early
as possible. The drawback of the signature file is that it is an inexact filter. A key word
(appearing in the query) surviving the checking may be not in the text. Therefore, a scan-
ning of the text has to be carried out to see whether the text really contains it. Further-


Source: Aberer, Karl - Faculté Informatique et Communications, Ecole Polytechnique Fédérale de Lausanne


Collections: Computer Technologies and Information Sciences