One of the key concepts for the support of geographical objects in GIS is the extensibility of database management systems. In this paper, we will show that its generalisation in an open distributed environment well supports the exchange of either (foreign) data or of (foreign) operations between multiple geo-databases and several GIS application systems and in particular between databases and application-specific computation services. This is a step towards the interoperability of several (semi-) autonomous GIS specific services with database services in a global GIS environment (GGIS). We will elaborate on the advantages of externally defined types for an improved exchange of objects between a geo-database system and several application systems in a multi-lingual environment. This includes the support of multiple representations often required for the same object. We will describe how remote computation services follow the same principle. Heterogeneity in both aspects, in the system platform as well as in the data representation can be overcome in a systematic and explicit way. At the same time the protection issue, hindering the conventional extensibility, is addressed. By using our Geo DASDBS prototype system we are able to present measurements that confirm that the cost overhead by external remote computation services is well invested in view of the increased flexibility we gain.