Some of the main principles are that data and metadata should not be managed centrally, but by the data originator and/or owner, and that tools and services connect via computer networks to the various sources. A GIS is often the platform for deploying an individual node within an SDI. To achieve these objectives, good coordination between all the actors is necessary and the definition of standards is very important.
A SDI should enable the discovery and delivery of spatial data from a data repository, via a spatial service provider, to a user. As mentioned earlier it is often wished that the data provider is able to update spatial data stored in a repository. Hence, the basic software components of an SDI are:
- a software client - to display, query, and analyse spatial data (this could be a browser or a Desktop GIS),
- a catalogue service - for the discovery, browsing, and querying of metadata or spatial services, spatial datasets and other resources,
- a spatial data service - allowing the delivery of the data via the Internet,
- processing services - such as datum and projection transformations,
- a (spatial) data repository - to store data, e.g. a Spatial database,
- GIS software (client or desktop) - to create and update spatial data
Besides these software components, a range of (international) technical standards are necessary that allow interaction between the different software components. Among those are geospatial standards defined by the Open Geospatial Consortium (e.g. OGC WMS, WFS, GML etc.) and ISO (e.g. ISO 19115) for the delivery of maps, vector and raster data, but also data format and internet transfer standards by W3C consortium.