Lutz M. Wegner

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A current research topic in the area of relational databases is the design of systems based on the Non First Normal Form (NF) data model. One particular development, the so-called extended NF data model, even permits structured values like lists and tuples to be included as attributes in relations. It is thus well suited to represent complex objects for(More)
Making use of the fact that two-level grammars (TLGs) may be thought of as finite specification of context-free grammars (CFGs) with “infinite” sets of productions, known techniques for parsing CFGs are applied to TLGs by first specifying a canonical CFG G′ — called skeleton grammar — obtained from the “cross-reference” of the TLG G. Under very natural(More)
We introduce ESCHER, a prototype database system based on the extended non-first-normal-form data model. The nested table approach is the paradigm for the graphical interface which allows browsing, editing and querying the database. Interaction is achieved by fingers generalizing the well-known cursor concept. We focus on interactive query formulation for(More)
Computer Supported Collaborative Work (CSCW) must present a shared workspace to co-operating users. This implies having a suitable engine at the client side which permits setting a focus on the shared data. Any concurrent activities of other users which happen to stretch into this viewport must also be made visible. Furthermore, the client must provide(More)