Visually Specifying Context

We introduce a simple and novel visual technique for the speci cation of context in structured documents called T-graphs that we base on T-con gurations in document trees. The technique is implemented in the current version of Designer. Although we are applying this technique in the speci cation of context-dependent style sheets for HTML, XML, and SGML documents, it is clear that it can be used in other environments such as query speci cation for structured documents and for computer program transformations. We compare T-graphs with the context speci cation techniques found in other style-sheet systems and we also provide examples of context that we can and cannot specify with T-graphs. Although Tgraphs are restrictive, they lend themselves to visual construction and modi cation, our main requirement when we designed this contextspeci cation method. We also investigate the time and space complexity of T-graph matching, a necessity for e cient implementation. The work of the three authors was supported partially by a joint DAAD-HK grant. In addition, the work of the third author was supported under a grant from the Research Grants Council of Hong Kong. Institut f ur Informatik, Technische Universitat M unchen, Arcisstr. 21, 80290M unchen, Germany. Email: fbrueggem, [email protected]. Department of Computer Science, Hong Kong University of Science & Technology, Clear Water Bay, Kowloon, Hong Kong. Email: [email protected].