Today, a promising approach to large-scale interoperability in geographic information systems (GIS) is a GIS implemented via a distributed object management system (DOMS) (e.g. CORBA, Java, OLE/COM) based on a standardized spatial object model (e.g. OGIS ). Geographic entities are available as location-and platform-independent objects, and are accessible via their interface, i.e. their attributes and a set of operations. Using a DOMS, much of the hardware, network and communication heterogeneity between interoperating GIS objects on different platforms and machines is handled automatically by the DOMS software, and is of no concern to the user. Also, via the notion of strongly typed object interfaces, type checking is also automatically performed at compile time to ensure that correct argument types are passed between interoperating GIS objects. However, to resolve the correctness of an argument passed from a GIS client to a GIS object, it is not sufficient to only verify the correctness of the type of the argument, but it is necessary to ensure that the content of an argument is matched. By content, we mean constraints related to the actual properties of an argument that are not easily captured in the type hierarchy. For example, let us assume that the operation “intersect() ” of the GIS object type “LineString ” has the following signature
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