Using the Azure Stream Analytics Query Language to Drive an ML Experiment
In the past I have talked about some of the components of Azure Machine Learning, but I thought it might make more sense to talk about creating a solution, rather than the individual components. As that will take a while, this post begins a multi-part series to bring in some real world examples to make the concepts around streaming data and Azure Machine Learning [ML] less abstract by starting with the data, adding several ML experiments, then talking about ways to implement the solution. The blog series is focused on the streaming data from a sample company the concrete company Eohs.
Streaming Data in Azure
Eohs has installed a vehicle tracking system which sends GPS positioning and sensor data which is sent back in near real time to the dispatching company. The dispatchers are able to monitor on their screens the location of the truck, speed, heading and some sensor information delivered every 20 seconds which allow them to know if the truck is loading concrete, pouring concrete, adding water, seat belt information, and if the passenger door is opened. Eohs has some policies for their drivers which can involve termination if they are violated. Drivers are not permitted to stop the truck anywhere other than the assigned delivery location, which cuts down on fraud and helps reduce insurance costs. This data is streamed via Azure Stream Analytics [ASA].
Cortana Analytics Implementation of Azure ML
Since Eohs is streaming their data with ASA, we want to implement an Azure ML Experiment to notify dispatch in real time any violation of their policies. As I discussed in a previous blog, since Cortana Analytics includes Azure ML and Stream Analytics, this would using the components is considered a Cortana Analytics implementation. We have created a Machine Learning Experiment which will look at the GPS position of the delivery location, and determine if a driver is stopped for an extra-ordinary length of time at a delivery location, as well as stopped in a non-delivery location. The dispatchers are immediately notified of this, so they can call the driver to figure out what is happening to the truck. What kind of data is needed to be sent to the Azure ML experiment to analyze?
Sliding Windows in Azure Stream Analytics
The Azure ML Experiment needs to evaluate all of the vehicle data which shows that the truck is stopped for a while, generally speaking greater than 90 seconds. After all some traffic lights take 90 seconds to get through, so eliminating the short stops would be helpful in decreasing the data needed to be evaluated. ASA uses a SQL-like query language which makes it easy to split the data so only the data that the experiment needs will be sent. We want to evaluate a window of time where data returned is only the data where the vehicle shows it is stopped for 91 seconds. Finding the 91 second stops is considered a sliding window. Here’s the code you would need to do this.
SELECT VehicleID, Avg(GPSLat), avg(GPSLong), min(Speed), max(PourSensor),Max(WaterSensor), dateadd(second, -91, System.Timestamp) as StartEvalTime , System.Timestamp as EndEvalTime FROM VehicleTrackingSystem TIMESTAMP by SensorTime Group by VehicleID, SlidingWindow(second,91) HAVING min(Speed) <1
EndEvalTime is the Time that this event was calculated by the system. Since I wanted both the start and end evaluation time, the time was calculated by using the DATEADD function. If one of the data elements arrived out of order, using the TIMESTAMP function will ensure that they events will be evaluated in the order they happened instead of the order when the data was received.
Other Windowing in Azure Stream Analytics
ASA also supports two other windowing functions, Tumbling and Hopping. In my next post I will be discussing how and when to use a Tumbling Window. If you are interested in reading the posts as they occur, please subscribe to desertislesql.com to be notified when the next post is available.
Data aficionado et SQL Raconteur