A framework for superimposed applications: Techniques to represent, access, transform, and interchange bi-level information

Superimposed applications (SAs) superimpose (that is, overlay) new information and structures (such as annotations) on parts (such as sub-documents) of existing base information (BI). In this setting, SA developers and users work with bi-level information, a combination of the superimposed information and the referenced BI parts.;We have designed a framework to assist SAs in the following bi-level-information-management activities: representation, access, transformation, and interchange. This framework defines the abstraction context agent to activate any BI part and to retrieve information from the context of the part. It includes means to represent and access bi-level information in a conceptual model (the Entity-Relationship model augmented with relationship patterns), the relational model, the XML model, and an object model. It defines a mechanism to transform bi-level information to alternative forms using queries expressed in existing query languages and executed by existing query processors. It also includes a formal model to improve the expression and execution of certain classes of queries. Finally, the framework employs the notion of SI dependency graphs to facilitate interchanging of bi-level information among SA users.;Specifically for the XML model, the framework defines Sixml, an XML markup language to represent bi-level information; Sixml DOM, an extension of the XML Document Object Model (DOM) to efficiently manipulate Sixml documents at run time; and Sixml Navigator, an alternative path navigator that improves both query expression and execution.;Using our framework, an SA can reference heterogeneous BI parts in situ, allowing multiple simultaneous organizations of the same BI parts, while preserving their original context. Also, the SA developer may employ the data model and schema that is appropriate for each SA.;We have evaluated each framework component using a method appropriate for the component. For example, we have implemented the context-agent abstraction to reference BI parts of the following types: Microsoft Word, Excel, and PowerPoint; XML, HTML, PDF, audio, and video. We have built six SAs that employ distinct schemas (in different data models). We have implemented the design of Sixml DOM and Sixml Navigator, used them with existing query processors, and experimentally evaluated the implementations' performance.