Ilwis objects form the core of the framework. They describe the main spatial datastructures and their supporting properties. Roughly speaking, functionality wise

Domain	Data type, or more correctly. The relation between internal values and their external representation
Ellipsoid	Mathematical approximation of the earth surface
Projection	Mathematics of coordinate transformations
CoordinateSystem	Reference system for uniquely defining spatial positions
Coverage	spatialt related data
RasterCoverage	one or more regular, equispaced grids which are spatially identically referenced
FeatureCoverage	a set of "things" with one or more spatial locations and a optional a set of attributes
Georeference	Mathematics to transform world coordinate to grid coordinates (raster) and vice versa
Table	Tabular data
OperationMetadata	Description of an operation: input and output,functionality and keywords
Catalog	Description of ilwis-objects in a container (e.g. folder, service)

The picture below gives a quick overview of the available Ilwis-objects.

Each IlwisObject has a location and a type uniquely identifying it. A location can be folder on disk, a URL in a service catalog (e.g. wfs), a link to ftp data, etcetera. Each combination can exist only once in one instance of the framework. This means that all 'copies' of an objects single instance are in reality the same object. This ensures automatic consistency of data across the system with the down side of needing some extra administration for this. This administration is controlled by the master-catalog.