  Concept drift refers to a non stationary learning problem over time. The
training and the application data often mismatch in real life problems. In this
report we present a context of concept drift problem 1. We focus on the issues
relevant to adaptive training set formation. We present the framework and
terminology, and formulate a global picture of concept drift learners design.
We start with formalizing the framework for the concept drifting data in
Section 1. In Section 2 we discuss the adaptivity mechanisms of the concept
drift learners. In Section 3 we overview the principle mechanisms of concept
drift learners. In this chapter we give a general picture of the available
algorithms and categorize them based on their properties. Section 5 discusses
the related research fields and Section 5 groups and presents major concept
drift applications. This report is intended to give a bird's view of concept
drift research field, provide a context of the research and position it within
broad spectrum of research fields and applications.
