Abstract
The Open Geospatial Consortium, Inc (OGC) Web Services (OWS) were initially primarily simple synchronous Web
services based on the HTTP transport protocol, which is perfectly valid in the case of simple geoprocessing of simple
data available from local sources. However, with the development of Web-based geospatial technologies, especially the
development of the Sensor Web, a number of limitations have been identified with using HTTP-GET/POST binding in
OGC OWS, which cannot meet the needs of asynchronous communication and operations between clients and services
or in OGC services chain. Asynchronicity in Web services could be achieved in different ways. Callback pattern is
widely supported in client asynchronous invocation. Message-based middleware often can be used together with the
asynchronous invocation alternatives. Web Notification Service (WNS) is designed to provide asynchronous messagebased
communication in OGC. This paper describes a mechanism for an asynchronous, message-based, event-driven,
dynamic geospatial Web system based on OGC Web services. The addition of asynchronicity in OGC Web services has
two components. One is the augmentation of OGC Web services with asynchronous message-based notification. The
other is asynchronous OGC Web service orchestration based on BPEL.
