Use of XML for Web-Based Query Processing of Geospatial Data

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New standards for geospatial data representation are emerging. For example, the ISO (the International Organization for Standardization) geospatial metadata draft standard defines a new object-oriented representation schema. Existing collections of geospatial data and metadata need tools to transform them to the new standard. This research investigated how mapping from existing geospatial metadata standards can be formally specified and implemented using XML. In addition, we investigated how large collections of geospatial data can be indexed to permit fast search for data queries combining spatial ranges with keywords and date range. To test out research ideas, we implemented the translation of Canadian NTDB (National Topographic Database) metadata files into the FGDC (Federal Geographic Data Committee) CSDGM (Content Standard for Digital Geospatial Metadata), which can then be translated into XML files. A tool for transforming FGDC CSDGM XML metadata files to ISO XML metadata files was designed and implemented in two ways: XSLT (eXtensible Style Language Transformations) and a Java program written for this research. A formal grammar for ISO geospatial metadata standard was proposed as a way of generating the XML DTD (Document Type Definition). Search engines for searching ISO XML metadata files on the Web by geospatial coordinates, dates and strings were developed by using a GSDindex (geospatial data index based on R-tree and AVL trees) approach and a relational(Oracle 8) database approach. Experiments comparing the two search engines on a testbed containing 6979 geospatial metadata files showed that, on average over a set of seven search experiments, the GSDindex approach was 2.5 times faster than the Oracle database approach.