Translating data between geographic information systems

Transferring data from one geographic information system (GIS) to another is difficult because of the diverse, and often complex, structure of transfer file formats. Accordingly, the design and implementation of an interface for transferring data from one format to another is time consuming and difficult. The translation may be performed by an interface constructed for the two formats (the individual interfacing strategy), by two interfaces through an interchange format (the interchange format interfacing strategy), or by a number of interfaces through a series of formats (the ring interfacing strategy). The interchange format interfacing strategy is widely adopted because it offers an acceptable compromise between the quality of the data translation and number of interfaces required. In contrast, the individual interfacing strategy achieves the best quality of translation but is generally rejected because of the impracticality of constructing a large number of interfaces. The goal pursued in this thesis is to maximise the quality of the translation by overcoming the impracticality of the individual interfacing strategy. This is achieved in the following way. An interface is divided into three phases: the decode phase, in which the source format decoder places data from the source format into a relational data base; the translate phase, in which the data is restructured according to a translation algorithm written in a relational query language; and the encode phase, in which the target format encoder places data from the relational data base into the target format. The time and effort involved in implementing these phases of data translation is minimised with the assistance of the following software tools: parser generators and lexical analysers which are used for generating format decoders; a relational data base management system which is used for implementing translation algorithms; and an encoder generator which is used for generating format encoders. The encoder generator is a new tool developed in this thesis. The efficacy of these tools is demonstrated, and a significant reduction in the effort of constructing interfaces is achieved, making the individual interfacing strategy a practical approach