OGC Sensor Web Standards and the “Smart City”
Sensors are everywhere. There are now thousands of sensors for every human on Earth. And there will be even more thousands in the future. At this year’s Consumer Electronics Show, applications that use sensors to monitor your home environment, track your luggage, the location of your pets, your weight and, in the case of a new “smart fork,” even how fast you eat are being demonstrated. Notice that the majority of these sensor based applications have a location element.
The concept of the smart city is similar: sensors will be integrated into the infrastructure of the city and the observations from these sensors will provide information used by applications ranging from hospital bed availability to optimized parking to better citizen safety to greater energy use efficiencies. Further, all of these sensors provide a location – whether there is in-situ or dynamic. And of course, there is the current market buzz about the Internet of Things (IoT) in which all sensor enabled devices are connected to the Internet.
However, there are numerous issues. These sensors are developed and manufactured by hundreds (thousands?) of different companies. This means that each manufacturer can (and does) have their own encodings for the observations and measurements from their sensors, different metadata for the sensor, different mechanisms for querying the sensor, different semantics for describing the sensor – you see the problem.
How can applications (and their developers) describe, task, and access observations in a standardized way from this huge variety of sensors being used in the built environment? How can the location aspects of the sensor be communicated in a standard way? Bringing some semblance of consistency and interoperability to the smart city sensor information domain threatens to make many current “big data” issues look trivial.
Since 2000, there has been and continues to be considerable activity in the OGC related to describing, tasking, and accessing network accessible sensors in a standardized way. This activity, labeled Sensor Web Enablement (SWE) has resulted in a mature and robust suite of OGC standards that include:
- Observations & Measurements Schema (O&M) –Defines conceptual models for encoding observations and measurements from a sensor, both archived and real-time.
- Sensor Model Language (SensorML) –Defines standard models and XML Schema for describing sensors systems and processes; provides information needed for discovery of sensors, location of sensor observations, processing of low-level sensor observations, and listing of taskable properties.
- Sensor Observations Service (SOS) – Specifies a standard web service interface for requesting, filtering, and retrieving observations and sensor system information. This is the intermediary between a client and an observation repository or near real-time sensor channel.
- Sensor Planning Service (SPS) –Specifies standard web service interface for requesting user-driven acquisitions and observations. This is the intermediary between a client and a sensor collection management environment.
These standards have been broadly implemented in numerous information domains such as ocean observing, glacial lake monitoring, satellite ground station systems, and tsunami warning systems. These standards are designed to provide an interoperability framework with standard interfaces and encodings for network accessible sensors regardless of the manufacturer or proprietary aspects of any given sensor. This is critical for the use of sensors in the smart city.
The true value of using OGC SWE standards in the Smart City is being realized with the integration of SWE standards into the software infrastructure that is used to support the use of low power sensors in the built infrastructure. A recent example is the integration of the SWE standards in to Contiki. From the website, “Contiki is an open source operating system for the Internet of Things. Contiki allows tiny, battery-operated low-power systems communicate with the Internet.” A 2012 paper titled, “Heterogeneous Sensors Become Homogeneous Things in Smart Cities” describes this work and the implications for the Smart City. Other IoT and Smart City projects and implementations using OGC standards with related infrastructures, such as Zigbee, are well documented in the literature.
Now that OGC SWE standards can be used as a key part of a standard platform for maximizing the use of heterogeneous sensor devices in the Smart City, there still remain a number of interoperability issues and requirements that need to be addressed. One issue is how to best “fuse” observations and measurements from these many sensors into decision support and command and control systems used in the Smart City. Another issue is semantic mediation. Different sensors observing the same phenomena may report the measurement in different units or semantics. Yet another issue is cybersecurity. How do we insure that these sensor systems cannot be easily hacked or attached by cyber terrorists? How can we best integrate crowd-sourced sensor location enabled content provided by smart mobile devices into applications for the Smart City?
These and other questions continue to provide the basis for lively and creative discussions in the OGC SWE community. Smart City sensor requirements will continue to drive these discussions, and will lead to enhancements and revisions to the current SWE standards baseline.