## 3 M2M Information and Services
### Sensor Web Enablement  
The term _Sensor Web_ refers to a wireless network of sensor nodes which autonomously share the data they collect and adjust their behavior based on this data [60; 61]. Today, it refers in practice into WWW overlay for integrating sensor networks and applications [62; 63; 64]. The view of _Sensor Web_ has been largely influenced by the architecture that is being developed by OGC SWE work group [56]. The SWE architecture represents a _logical view-point_ of the _Sensor Web_, as an infrastructure which enables an interoperable usage of sensor resources by enabling their discovery, access, tasking, as well as events and alerting, in a standardized way [63]. The SWE architecture consists of two main blocks: Interface model and Information model. The information model, formalized as XML schema documents, consists of the conceptual data models. The interface model (services model), is the specification of services in the form of Web service interface specifications (WSDL). Figures 2 and 3 show the new generation SWE standards (Version 2.0) which were published in the second half of 2011. Green boxes are specifications approved as standards (or in standardization process), grey boxes are discussion papers and dashed arrows point to dependencies. SWE Common specifies low level data models for exchanging sensor related data between SWE framework nodes. It defines the representation, nature, structure and encoding of sensor related data [65]. Observations & Measurements (O&M) defines a conceptual schema for observations, and for features involved in sampling when making observations. These provide models for the exchange of information describing observation acts and their results, both within and between different scientific and technical communities [66]. SWE services use SensorML as a format for describing their associated sensors [67]. The model provides information needed for discovery of sensors, location of sensor observations, processing of low-level sensor observations, and listing of configurable sensor properties. A sensor is defined as a process which is capable of observing a phenomenon and returning an observed value. For example, a process can be a measurement procedure conducted by a sensor or the post processing of previously gathered data. Event Pattern Markup Language (EML) defines subscription filters to SWE framework nodes that provide publish/subscribe type services. Currently, the Sensor Event Service (SES) is the first prototype within OGC SWE that supports EML. Both the O&M and SensorML models extend the OGC's Geographic Markup Language (GML) which is a standard XML encoding for expressing geographical features. This provides the functionality to integrate sensors into Spatial Data Infrastructures (SDI). SWE Service Model defines packages with data types and operation request and response types for common use across SWE services [68]. Sensor Observation Service (SOS) provides standardized access to sensor observations and sensor metadata [69]. The service acts as a mediator between a client and a sensor data archive or a real-time sensor system. The heterogeneous communication protocols and data formats of the associated sensors are hidden by the standardized interface of SOS. SOS defines O&M as its mandatory and default response format for sensor data and recommends the usage of SensorML for sensor metadata exchange. Sensor Planning Service (SPS) is a web service interface that allows clients to submit tasks to sensors for operations such as the configuration of the sampling rate or the steering of a movable sensor platform [70]. SPS operations derive from the abstract request type defined by SWE Service Model and aggregates operations covering the complete process of controlling and planning sensor tasks. Sensor Event Service (SES) is a SWE service specification at discussion phase. It provides a push-based access to sensor data as well as functionality for sensor data mining and fusion inside a spatial data structure.