XQuery as a retrieval mechanism for longitudinal multiscale forest resource data

In most forested environments, boreal forest in particular, monitoring and evaluation of management activities would be facilitated by storage of multiscale data sets spanning long time periods. For this study, such a data repository based on a generic spatio-temporal conceptual data model was created using XML. The data repository containing changes in data content for a 1000 ha forest estate between 1871 and 1994 was used to evaluate the data retrieval capabilities of XQuery. The data retrieval operations consisted of pivoting, sequencing, and aggregation. Pivoting transforms the generic attribute storage used in the data model into a more compact column-wise format. Sequencing is used to return a temporal sequence of values, and for the traversal of the object hierarchy. Aggregation aggregates the values of a variable over a grouping variable. The combinations of the basic retrieval operations were also investigated as well as the effect of time and object hierarchy on the retrieval operations. The conceptual match between the generic spatio-temporal data model and the XML data model was apparent at the data retrieval operations. The key properties of XQuery for the implementation of the retrieval operations were extendability, support for nested structures, and data transformation functionality.