HB2 : a hyperbase management system for open, distributed hypermedia system architectures

Abstract

The complexities of providing data management support for advanced hypermedia computing environments make it clear that effectiveness requires more than simple extensions to existing database technology. This dissertation presents the conceptual design, prototypic implementation, and qualitative evaluation of the HB2 hyperbase management system (HBMS). The overarching goal for HB2 is to provide as much flexibility and extensibility as possible in support of advanced hypermedia system architectures. A particular emphasis is placed on accommodating application-level extensibility through inter-application linking. HB2 represents a new approach to HBMS organization. Its subsystems include: the Hyperbase Session Manager (HSM), Object Manager (OM), Association Set Manager (ASM), Off-line Services Manager (OSM), and the Storage Manager (SM). OM implements the notion of a large, shared repository of simple, unstructured objects. ASM provides persistent and sharable storage for the connectivity data that link information together to form hypermedia. ASM also manages separate contexts for these structural data. Together, OM and ASM implement HB2's data model, which abstracts inter-object connectivity, behaviors, and information from hypermedia. SM maps HB2's data model into physical storage. Distribution of OM and ASM functionality across a range of platforms is achieved by a client/server model using interprocess communication facilities. HSM controls access to the OM and ASM servers and manages sessions. Transaction management instantiates separate and tailored mechanisms for deadlock-free concurrency control over objects, structural data, and contexts. OSM asynchronously enforces integrity constraints over OM and ASM data. A framework for hyperbase extensibility and scalability is provided by virtue of HB2's modular subsystem organization. HB2 addresses several critical HBMS design issues. Central to HB2 is the notion that effective support for hypermedia requires tailored support for the essential entities that comprise hypermedia. This leads to a new and empowering approach to hyperbase organization. Data management support is provided to the information and behavioral elements of hypermedia independently of its structural elements. In addition, the work advances a notion of object that has been refined to the particular requirements of hypermedia and provides a context for thinking about the eventual incorporation of hypermedia functionality into the base operating environment.