## 3 New Generation Sensor Web Enablement
### Evolvement of SWE Information Model
#### 3.2.1 Common SWE Data Types  
Common and basic data types used throughout the SWE framework are defined by SWE Common. The first version of the SWE Common data model and its encoding was defined within the document of the SensorML 1.0 standard. Data types defined in this data model are used as input parameters of SWE service operations or as the basis for complex types. In the first generation SWE, this common model was strongly used in SensorML, but also the interface models of SOS 1.0, SPS 1.0, and SAS referenced the SWE common data types. In O&M 1.0, it was also possible to use SWE Common for the encoding of observation results; however, there was no formal dependency between these two specifications. In the new generation of SWE, the position of SWE Common 2.0 [58] is strengthened. It is specified in its own standard document, independent of SensorML, and is formally referenced by the new SWE specifications. The main goal of SWE Common 2.0 is to enable the description and provision of _data_ in an interoperable way. Therefore, the data model contains four main pieces of information: _representation_ of data values (e.g., categorical, numeric, or textual), _nature_ of data by referencing to semantic \begin{table}
\begin{tabular}{|l|l|} \hline
**Specification** & \multicolumn{2}{|c|}{**Description of change**} \\ \hline  & Extracted to separate specification document \\  & Separation of conceptual model and its implementation \\ SWE Common 2.0 & Independence from Geography Markup Language \\  & Improved definition of data stream encodings \\  & Extension point mechanism \\ \hline  & Separation of conceptual model and its implementation \\  & Conceptual model has become ISO standard \\ O\&M 2.0 & Spatial profile has been added \\  & New observation properties (e.g., _valid time_ and _related observation_) \\  & Revision of terminology (e.g., _sampling time_ renamed to _phenomenon time_) \\  & Dropping of _observation collection_ type \\ \hline SensorML 2.0 (_in progress_) & Property inheritance mechanism (_under discussion_) \\  & Sensor interface description (_under discussion_) \\  & Profiles have been defined (e.g., SensorML for Discovery) \\ \hline TML & _No evolvement_. Not mentioned in the specifications of the new generation \\ \hline EML & New specification which adds functionality for complex event processing \\ \hline \end{tabular}
\end{table} 
Table 1: Major changes from the first to the new generation of the SWE information model. descriptions, _quality_ of data, and data _structure_ defining how individual pieces of data are grouped, ordered, and repeated to form a complete data stream. Besides simple data component types (e.g., Text or Boolean), SWE Common 2.0 contains aggregate types (e.g., Record, or Vector). Instances of aggregate types can carry multiple data components, for example to describe the structure of a sensor data stream. The individual data components have properties to define their quality or link to their semantics stored for example as concepts in ontology repositories. SWE Common 2.0 separates the conceptual model from its implementation. Based on the conceptual model different implementations may be defined; included in SWE Common 2.0 is an XML implementation of the model. The definition of binary, textual and XML based data stream encodings has been improved. For example, the XML encoding now enables sensor data to be described and provided in simple XML format. Direct support for multiplexed encodings and standard encodings has been removed. However, additional encodings can be defined as extensions to the core SWE Common standard. The model for describing observable phenomena based upon a dictionary structure defined by the Geography Markup Language (GML) [59] has been removed. This emphasizes the fact that SWE Common 2.0 does not depend on or favors a specific approach for modeling phenomena. A SWE Common data component simply references a concept that provides its definition--which can be an entry in a dictionary, thesaurus, or ontology.