# Middleware for Plug and Play Integration of Heterogeneous Sensor Resources into the Sensor Web
## 2 Sensor Integration into Observation Platforms  
### Requirement Analysis  
When integrating new sensor resources into existing data infrastructures, several standardized operations are required. These operations can be classified in two different levels: Instrument Level, and Sensor Web level [5]. The Instrument Level operations are related to the sensor's operational challenges, focused on the sensor-platform interaction, including both sensor configuration and sensor data retrieval. The Sensor Web challenges are related to the sensor data management, including standardized data encodings, sensor data discovery, tasking mechanisms, etc.  
According to previous work on this topic, at least four operations are required at the instrument level: sensor detection, sensor identification, sensor configuration and simple measurements operations [5]. These are operational requirements, focused on the direct sensor-platform interaction.  
From the data management side, there is a multitude of operations that can be realized, such as data discovery, data access, sensor tasking, events and notifications, etc. However, this work focuses on the integration of sensors to the Sensor Web from a platform operator point of view. Thus only the sensor registration and sensor data ingestion operations are considered within this work.  
Some ocean observation platforms present additional constrains such as limited power availability and low-bandwidth communications. These platforms are usually based on low-power embedded systems, with limited computational capacity. Thus, a sensor plug and play mechanism should take into account these constrains. Summarizing, the requirements to achieve plug and play integration into observation platforms are:  
1. **Sensor Detection**: Detect a new sensor when it is attached to an observation platform. The host platform controller should be able to detect a new sensor without human intervention.
2. **Sensor Identification**: Obtain an unambiguous description of the sensor, including all the metadata to identify the sensor (unique ID, sensor model, etc.) and all information required to register the sensor to an existing Sensor Web server.
3. **Sensor Configuration**: This requirement addresses all operations required before the platform can start retrieving data from a sensor. This includes establishing a communication link between the platform and the sensor and applying any configuration required by the sensor (i.e., activate a specific acquisition channel, set the sampling rate, etc.).
4. **Simple Measurements Operations**: Those operations that are directly related to the retrieval of data. These operations may be actively querying the sensor for data or listening to data streams. Also knowledge of the data interface provided by the sensor is required in order to parse, process and store the data.
5. **Sensor Registration**: Registering a sensor to existing Sensor Web server requires a considerable amount of metadata organized and structured in a coherent way, including physical parameters that are being measured (observable properties), computational representation of the real-world feature that is being measured (feature of interest), alongside with other sensor characteristics. Furthermore, the meaning of this metadata has to be made explicit and understandable by machines, thus, controlled vocabularies containing formal definitions shall be used [27].
6. **Data Ingestion**: Once the sensor is registered, the data measured by this sensor has to be ingested to the server, where it will be archived.
7. **Resource Constrains**: Any plug and play mechanism aimed to integrate sensors into marine data acquisition platforms should be able to work in low-bandwidth, low-power and computationally-constrained scenarios.