ToX (The Toronto XML Engine) is a research project of the Database Group in the Department of Computer Science at the University of Toronto. The Toronto XML Server is "a repository for XML data and metadata, which supports real and virtual XML documents. Real documents are stored as files or mapped into relational or object databases, depending on their structuredness; indices are defined according to the storage method used. Virtual documents can be remote documents, defined as arbitrary WebOQL queries, or views, defined as queries over documents registered in the system. The system catalog contains metadata for the documents, especially their schemata, used for query processing and optimization. Queries can range over both the catalog and the documents, and multiple query languages are supported."

Abstract from the Santa Barbara 2001 paper: "Indexing schemes for semistructured data have been developed in recent years to optimize path query processing by summarizing path information. However, most of these schemes can only be applied to some query processing stages whereas others only support a limited class of queries. To overcome these limitations we developed ToXin, an indexing scheme for XML data that fully exploits the overall path structure of the database in all query processing stages. ToXin consists of two different types of structures: a path index that summarizes all paths in the database and can be used for both forward and backward navigation starting from any node, and a value index that supports predicates over values. ToXin synthesizes ideas from object-oriented path indexes and extends them to the semistructured realm of XML data. In this paper we present the ToXin architecture, describe its current implementation, and discuss comparative performance results..."

Princpal investigators in the ToX Server project include Alberto O. Mendelzon, Attila Barta, Flavio Rizzolo, Denilson Barbosa, Marcelo Arenas, Angus Stewart, Ramona Truta, Patricia Rodriguez Gianolli, Greg McArthur, and George Andrei Mihaila.