This lets public transit passengers answer questions like:
- "My train is getting later and later, is it actually moving?"
- "My train is getting later and later, has it actually STARTED its journey?" (sometimes the answer is "no", sadly)
- "Is it just my train, or are many trains running late?"
- "What was the on-time performance of this train like yesterday? 2 days ago? 7 days ago?" (Some trains tend to be chronically late)
It may come as a surprise that the backend of the system is actually not a database, but Splunk (http://www.splunk.com). DBs are nice, but Splunk is fantastic when it comes to data analytics and reporting.
I'm currently waiting for Splunk to make some of their machine learning modules available for free so that I can start pulling in weather data, train the machine learning component against both that and the train data, and use that to predict the likelihood of any given train becoming late.