## 3 New Generation Sensor Web Enablement
### Introduction to OGC's Sensor Web Enablement Initiative  
The _Open Geospatial Consortium_ (OGC) is an international, non-profit standardization organization comprising over 400 companies, governmental agencies and universities. Those members are participating in a consensus process to develop standards for data models and (Web) services for enabling the _Geospatial Web_ which integrates the World Wide Web with spatiotemporal data and services.  
The OGC SWE working group was founded in 2003. As part of OGC's specification program, the SWE working group develops standards to integrate sensors into the Geospatial Web for enabling a specialized subtype, the _Sensor Web_. Therefore, SWE has specified a number of standards defining formats for sensor data and metadata as well as service interfaces which enable the interoperable access to real and virtual sensor resources (simulation models are examples for virtual sensor resources [50]). The SWE 1.0 specifications have been approved as standards between 2006 and 2007. They offer the following functionalities:  
* _Description of sensor data_ to enable further processing.
* _Description of sensor metadata_ including properties and behavior of sensors, as well as correlating reliability and accuracy of collected measurements.
* _Access to observations and sensor metadata_ based on standardized data formats and appropriate query and filter mechanisms.
* _Tasking of sensors_ for the acquisition of measurement data.  
Further, the following functionalities are supported by the first generation SWE, but are not yet approved as standards:  
* _Alerting_ based on sensor measurements and defined alert criteria.
* _Notification_ of end users in case of alerts or finished sensor tasks via e.g., SMS or e-mail.  
The new generation of SWE adds further functionalities to the SWE framework, which is also not yet approved as standards:  
* _Eventing_ mechanisms which advance the basic alerting functionality of the first generation SWE specifications.
* _Discovery_ of sensor resources and sensor observables.  
To provide the above mentioned functionalities the specifications of the first as well as the new generation SWE are divided into two informal subgroups. First, the _information model_ includes the data models and encodings. Second, the _interface model_ comprises the different web service interface specifications (the interface model was formerly called service model and to avoid naming confusion with the SWE Service Model standard [51], which is part of the new generation SWE, we propose this renaming). In the next subsections, the two parts of the SWE framework are described, it is illustrated how the functionalities listed above are realized, and the changes from first to new generation SWE are analyzed.  
A non-functional, but formal change which concerns all new SWE standards or candidate standards is the application of OGC's new modular specification model [52]. By applying these guidelines to structure and design the specification document, numerous _requirements_ are formulated throughout the specifications. These requirements convey criteria which need to be fulfilled if compliance with the standard is claimed. This improves the strictness of a specification and facilitates conformance testing of compliant software components. However, only very few OGC standards which are compliant with this new model have been published yet, therefore, experiences regarding ease of use and level of achieved interoperability are still outstanding. Nevertheless, it is expected that the advantages of the new specification model overcompensate the disadvantages such as degraded readability and the explosion of standard production costs.