Machine learning is a branch of applied computer science in which we build models of real-world phenomenon based on existing data available for analysis, and then using that model, predicting certain characteristics of data never seen before by the model. Machine learning has become a very important component of real-time applications as decisions need to be made in real time.

Graphically, the process of machine learning can be represented by the following figure:

The process of building the model from data is called training in machine learning terminology. Training can happen in real time on a stream of data or it can be done on historical data. When the training is done in real time, the model evolves over time with the changed data. This kind of learning is referred to as online learning, and when the model is updated every once in a while, by running...