Querying bi-level information

In our research on superimposed information management, we have developed applications where information elements in the superimposed layer serve to annotate, comment, restructure, and combine selections from one or more existing documents in the base layer. Base documents tend to be unstructured or semi-structured (HTML pages, Excel spreadsheets, and so on) with marks delimiting selections. Selections in the base layer can be programmatically accessed via marks to retrieve content and context. The applications we have built to date allow creation of new marks and new superimposed elements (that use marks), but they have been browse-oriented and tend to expose the line between superimposed and base layers. Here, we present a new access capability, called bi-level queries, that allows an application or user to query over both layers as a whole. Bi-level queries provide an alternative style of data integration where only relevant portions of a base document are mediated (not the whole document) and the superimposed layer can add information not present in the base layer. We discuss our framework for superimposed information management, an initial implementation of a bi-level query system with an XML Query interface, and suggest mechanisms to improve scalability and performance.