# A Model Based Framework for IoT-Aware Business Process Management
## 3 Background
### SWE Framework and SSN Ontology  
A significant challenge in the IoT field comes from the heterogeneity of the physical layer. In an interconnected sensors network, heterogeneous physical entities, provided by different vendors and operating according to specific rules and protocols, must cooperate to achieve the required objectives. An IoT system that aims at collecting and processing the flow of data coming from orchestrated devices must introduce appropriate methods and tools for the seamless interaction with various devices. In this respect, the interoperability should be addressed from two perspectives:  
* _Technical_ and _syntactical interoperability_ should be ensured by introducing standards and technologies that enable an IoT system to interact with various devices, each using different implementation technologies and communication protocols;
* _Semantic interoperability_ should also be ensured in order to make sensor data easily understandable by various actors, including IoT system components in charge of automatically processing the flow of data collected by the sensor network. In this respect, this paper exploits the OGC Sensor Web Enablement standard [16] and the OGC-W3C Semantic Sensor Network (SSN) ontology [13], respectively. The Sensor Web Enablement (SWE) is a framework promoted by the Open Geospatial Consortium (OGC) for supporting the development of the so-called _Sensor Web_, i.e., a collection of sensors and sensors networks provided and controlled by different owners and interconnected by use of the web platform. The SWE initiative has been started in 2003 and has progressively addressed the development of data models, encoding methods and service interface specifications to provide a set of features that includes:  
* _Retrieval of real-time or time-series observations_, along with their coverage in standard encodings;
* _Access to sensor settings_ that allow the software to automatically process and geo-locate data;
* _Tasking of sensors_ to obtain observations of interest;
* _Subscription to and publication of warnings_ to be sent by sensors or sensor services based on particular criteria. Among the various standards currently included in the SWE Framework, this paper specifically exploits the following two:  
* _Observations & Measurements Schema (O&M)_, which provides data models and XML Schemas for encoding historical observations, real-time observations and measurements retrieved by sensors;
* _Sensor Model Language (SensorML)_, which introduces models and XML Schemas for describing the observation processing systems;
* _Sensor Observation Service (SOS)_, which specifies an open interface for interacting with sensors and collecting measurement data. As regards the definition of ontologies for the semantic description of sensor devices, observation processes, and measurement results, one of the most prominent results has been achieved by the joint work of the World Wide Web Consortium (W3C) and the OGC Consortium, which promoted the Semantic Sensor Network (SSN) Ontology [13]. SSN provides a flexible but coherent perspective for the conceptual description of the entities, relations and activities involved in the measurement process. The pillars of the proposed approach can be summarized in the following concepts defined by SSN:  
* _System_: an abstraction of physical infrastructures that implement _procedures_;
* _Sensor_: entity (device, human or automated system, e.g., a software) involved in a _procedure_;
* _Procedure_: a sequence of activities or a protocol carried out to make an _observation_;
* _Observation_: action executed to measure, estimate or calculate the actual value of an _observable property_ related to a _feature of interest_.