[1] Kottman, Cliff (ed.), OpenGIS Abstract Spec topic 12: OpenGIS Service Architecture, version 4 (1999): http://www.opengis.org/techno/specs.htm.
[2] Buehler, Kurt and McKee, Lance (eds.), OpenGIS Guide, 3rd edition draft (1999): http://www.opengis.org/techno/guide.htm.