# Middleware for Plug and Play Integration of Heterogeneous Sensor Resources into the Sensor Web
## 7 Conclusions and Future Work  
In this work a framework to enable plug and play sensor integration into research data infrastructures have been proposed. It is based on the combination of different standards from the OGC's SWE framework and the W3C consortium. Using these standards a set of interoperable components have been presented to bridge between any kind of (in-situ) sensor and the Sensor Web. To ensure re-usability of the results aspects such as cross-platform support and the use of open source licenses were emphasized. These components can be easily adapted to different scenarios without any significant modification, overcoming the intrinsic constraints of ocean observation platforms. Sensor's metadata, as well as deployment and acquisition-specific metadata are combined in a coherent format by using the concepts of SDF, providing a SensorML-based template for unambiguous sensor deployment and sensor operation description. The advantages of the combination of SDFs with the proposed acquisition chain (SWE Bridge, SOS Proxy and SOS server) has been demonstrated in three real-world scenarios. These deployments include a mobile platform with severe power and communications constraints (SeaExplorer Glider), a multidisciplinary fixed-point observation platform with a pack of commercial sensors (EGIM), and a complex seismic system (INTMARSIS system). Different sensors where integrated into observation platforms, including six COTS sensors, two newly developed OGC PUCK-enabled sensors and a complex seismic system (treated as three Virtual Instruments), each one of them with their own non-standardized proprietary protocols. The design of the presented components and their SensorML descriptions provide the foundations for generating automated processes that can combine sensor metadata and acquisition chain metadata so that SDFs can even be created in a semi-automated manner. Further work in this field should be focused on facilitating the application of the presented sensor acquisition chain by making the generation of SDFs easier. For example developing a user-friendly graphical user interface to generate SDFs with minimal human intervention. This tool should be able to combine the information from the sensor, the description of the acquisition chain's components and the capabilities of SOS servers in order to allow users to generate their own configuration files in an intuitive manner, hiding the specificities of the SWE standards from the end user. This would allow \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sensor Name**} & \multicolumn{4}{c}{**Sensor Parameters**} & \multicolumn{4}{c}{**SWE Bridge Performance**} \\ \cline{2-9}  & **Protocol** & **Stream** & **Period** & **SDF Size** & **Max Heap** & **Avg Heap** & **Avg Stack** & **CPU Load** \\  & **(bytes)** & **(s)** & **(bytes)** & **(kBytes)** & **(kBytes)** & **(kBytes)** & **(kBytes)** & **(kBytes)** \\ \hline A1 & Serial & 61 & 1 & 3158 & 40.05 & 13.26 & 1.631 & 35.23 \\ Mini.1 & Serial & 68 & 1 & 2451 & 36.63 & 10.96 & 1.568 & 34.50 \\ \hline Aanderaa 4831 & TCP & 80 & 1 & 3440 & 38.36 & 10.93 & 1.029 & 88.36 \\ Workhorse & TCP & 688 & 60 & 9431 & 63.66 & 36.43 & 0.830 & 78.23 \\ Eco NTU & TCP & 32 & 1 & 3290 & 36.93 & 9.53 & 0.892 & 78.26 \\ SBE 37 & TCP & 72 & 10 & 3429 & 37.91 & 10.22 & 0.740 & 68.39 \\ SBE 54 & TCP & 140 & 1 & 2769 & 35.56 & 8.05 & 0.895 & 87.35 \\ EGIM & UDP & 137 & 20 & 4477 & 42.57 & 14.70 & 0.691 & 68.03 \\ \hline Seismic Data & UDP & 10 & 10 & 1728 & 29.96 & 5.84 & 0.692 & 63.61 \\ OBS Technical & UDP & 30 & 30 & 1764 & 29.76 & 6.02 & 0.683 & 63.75 \\ Buoy Status & UDP & 30 & 30 & 1764 & 29.96 & 6.32 & 0.685 & 63.89 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: SWE Bridge performance assessed when interfacing sensors from the NeXOS, EMSODEV and INTMARSIS projects. The average values of the memory consumption are calculated in the stationary phase (after the setup).