modifications to the process or by simulating the observation with a known signature source. On-demand processing of Observations - Process chains for geolocation or higher-level processing of observations can be described in SensorML, discovered and distributed over the web, and executed on-demand without a prior knowledge of the sensor or processor characteristics. This was the original driver for SensorML, as a means of countering the proliferation of disparate, stovepipe systems for processing sensor data within various sensor communities. SensorML also enables the distribution of processing to any point within the sensor chain, from sensor to data center to the individual user's PDA. SensorML enables this processing without the need for sensor-specific software. Support for tasking, observation, and alert services - SensorML descriptions of sensor systems or simulations can be mined in support of establishing OGC Sensor Observation Services (SOS), Sensor Planning Services (SPS), and Sensor Alert Services (SAS). SensorML defines and builds on common data definitions that are used throughout the OGC Sensor Web Enablement (SWE) framework. Plug-N-Play, auto-configuring, and autonomous sensor networks - SensorML enables the development of plug-n-play sensors, simulations, and processes, which may be seamlessly added to Decision Support systems. The self-describing characteristic of SensorML-enabled sensors and processes also supports the development of auto-configuring sensor networks, as well as the development of autonomous sensor networks in which sensors can publish alerts and tasks to which other sensors can subscribe and react. Archiving of Sensor Parameters - Finally, SensorML provides a mechanism for archiving fundamental parameters and assumptions regarding sensors and processes, so that observations from these systems can still be reprocessed and improved long after the origin mission has ended. This is proving to be critical for long-range applications such as global change monitoring and modeling. What are the essential elements? Component - Physical atomic process that transforms information from one form to another. For example, a Detector typically transforms a physical property or phenomenon to a digital number. Example Components include detectors, actuators, and physical filters. System - Composite physically based model of a group or array of components, which can include detectors, actuators, or sub-systems. A System relates a Process Chain to the real world and therefore provides additional definitions regarding relative positions of its components and communication interfaces. Process Model - Atomic non-physical processing block usually used within a more complex Process Chain. It is associated to a Process Method which defines the process