The Niagara Internet Query System.

To handle infinite streams and data sources with unpredictable rates, the Niagara Internet Query System supports a “get partial” operation on blocking operators in order to produce partial query results, and inserts synchronization packets at critical points in the operator tree to guarantee the consistency of (partial) results.

Abstract

: Many projections envision a future in which the Internet is populated with a vast number of Web-accessible XML files---a "World-Wide Database". Recently, there has been a great deal of research into XML query languages to enable the execution of database-style queries over these XML files. However, merely being an XML query-processing engine does not render a system suitable for querying the Internet. A truly useful system must provide mechanisms to (a) find the XML files that are relevant to a given query, and (b) deal with remote data sources that either provide unpredictable data access and transfer rates, or are infinite streams, or both. The Niagara Internet Query System was designed from the bottom-up to provide these mechanisms. It finds relevant XML documents by using a novel collaboration between the Niagara XML-QL query processor and the Niagara "text-in-context" XML search engine. To handle infinite streams and data sources with unpredictable rates, it supports a...