Proximal Nodes: a Model to Query Document Databases by Contents and Structure

A model to query document databases by both their content and structure is presented. The goal is to obtain a query language which is expressive in practice while being eeciently imple-mentable, features not present at the same time in previous work. The key ideas of the model are a set-oriented query language based on operations on nearby structure elements of one or more hierarchies, together with content and structural indexing and bottom-up evaluation. The model is evaluated regarding expressiveness and eeciency, showing that it provides a good trade-oo between both goals. Finally, it is shown how to include in the model other media diierent from text. 1. INTRODUCTION Document databases are deserving more and more attention, due to their multiple applications: digital libraries, ooce automation, software engineering, automated dictionaries and encyclopedias, etc. Frakes and Baeza-Yates 1992] The purpose of a document database is to store documents, structured or not. A document database is composed of two parts: content and (if present) structure. The content is the data itself, while the structure relates diierent parts of the database by some criterion. Any information model for a document database should comprise three parts: data, structure, and query language. It must specify how is the data seen (i.e.