Abstraction and Decomposition in Interoperable GIS

ion and Decomposition in Interoperable GIS Agn es Voisard Heinz Schweppe Institut f ur Informatik Freie Universitat Berlin Takustr. 9 D-14195 Berlin fvoisard,[email protected] Abstract With the advent of distributed computing and the increasing trend towards the reuse of geographic data, a new generation of geographic information systems (GIS) is currently being speci ed. The key characteristics of these interoperable GIS 1 are modularity and extensibility, and they are composed of existing software systems such as database management systems, traditional GIS, statistics packages and simulation models. They can be de ned in terms of generic frameworks which facilitate both information exchange between participating systems and the addition of new functionalities. Even though the idea of de ning open GIS is not new, it is crucial that the steps necessary to design such a complex system be clearly decomposed. In this paper, we propose a layer decomposition for the design of an open GIS. Each layer corresponds to a di erent level of abstraction, starting with the application or user level down to the invocation of systems services. In addition, each such level can be speci ed by the same set of concepts: operation, data and session (ODS concepts). Orthogonally, the metadata needed for the interaction between levels is indispensable to achieve openness. The declarative style of specifying both user interaction and implementation on di erent levels of abstraction facilitates the incorporation of new software components. Therefore, the framework introduced in this paper supports the design and the evolution of interoperable GIS. Part of this work was carried out while this author was visiting the International Computer Science Institute, Berkeley, CA. 1We use the terms interoperable GIS and open GIS interchangeably, however Open GIS (OGIS) is a trademark of the Open GIS Consortium (ODC). 1