## 3 New Generation Sensor Web Enablement
### Improved Sensor Description Management  
Metadata on sensors is a very important part of SWE (Section 3.2.3). SOS 1.0 defined a _DescribeSensor_ operation with which the current sensor description could be retrieved. SPS 1.0 achieved this functionality by directly referencing the description from within its capabilities \begin{table}
\begin{tabular}{|l|c|} \hline
**Specification** & **Description of change** \\ \hline  & Common capabilities content model: \\  & \(\bullet\) Property inheritance mechanism to decrease size of capabilities documents \\  & \(\bullet\) Introduction of _abstract offering_ as base for offering types of specialized services \\  & Extensibility points for operation requests, responses and other data types \\  & Improved sensor description management: \\  & \(\bullet\) a sensor description is format agnostic according to O\&M design principles and facilitates revision management \\  & \(\bullet\) definition of a common _DescribeSensor_ operation for retrieval of sensor descriptions \\  & \(\bullet\) definition of a common _UpdateSensorDescription_ operation for modification of existing \\  & Sensor descriptions \\  & Conceptual models for sensor insertion and deletion operations (_RegisterSensor_ and _DeleteSensor_) \\  & Basis for SWE service eventing introduced by defining a notification package to support \\  & publication of SWE service events and provision of notification metadata \\  & Revised identifier handling to harmonize identifier usage across the SWE specifications \\  & Definition of rules that enable automatic mapping between conceptual model and XML Schema \\  & implementation \\  & SOAP binding introduced \\ \hline \end{tabular}
\end{table} 
Table 2: Major changes introduced by SWE Service Model 2.0.  
document. In the new generation of SWE, this has been harmonized through a common _DescribeSensor_ operation defined by SWES. This operation enables clients to retrieve not only the current description of a given sensor, but also descriptions that were valid in the past or will become valid in future. This is useful to track changes in a sensor description, regardless of the format that the description is given in--keeping in mind that SWE 2.0 does not mandate a specific description format to support the requirements of different domains, though SensorML is recommended. A common use case that is supported through such time tagged sensor descriptions is when a sensor is mobile. There, the sensor location could be provided as part of the sensor description. Further, SWES defines the _UpdateSensorDescription_ operation which allows updating sensor descriptions. Therefore, SWES defines precise rules how to handle situations in which the validity time of a submitted sensor description and an already existing sensor description temporally interact. This enables sensor providers to manage a revision history of metadata for a given sensor through a standardized interface. Conceptual Models for Sensor Insertion and Deletion  
Only SOS 1.0 defined an operation (_RegisterSensor_) to support the insertion of new sensors. However, the model of that operation, and in particular the association of the new sensor with offering specific metadata, was insufficient. The SWE Service Model defines the conceptual model of an _InsertSensor_ operation which replaces the _RegisterSensor_ operation. The _InsertSensor_ operation now includes all the information items required to populate a SWE service offering (e.g., properties observable by the new sensor or features related to that sensor). Metadata specific for a certain type of SWE service (e.g., SOS or SPS) can be added via a well-defined extension point and sub typing the abstract _InsertionMetadata_ parameter. While SOS 2.0 leverages this model, neither SPS 1.0 nor SPS 2.0 enables the insertion of sensors. This is due to the fact that the implementation of an SPS, which is generic enough to support all possible realizations of tasking logic and connections to the underlying sensor system, is very difficult.