We live in a world where our daily routine involves multiple contact points with the digital world. We have computers assisting us with communication, travel, entertainment, and whatnot. The digital online products (apps, websites, software, and so on) that we use seamlessly all the time help us avoid mundane and repetitive tasks. These software have been developed using computer programming languages (like C, C++, Python, Java, and so on) by programmers who have explicitly programmed each instruction to enable these software to perform defined tasks. A typical interaction between a compute device (computer, phone, and so on) and an explicitly programmed software application with inputs and defined outputs is depicted in the following diagram:

Though the current paradigm has been helping us develop amazingly complex software/systems to address tasks from different domains and aspects in a pretty efficient way, they require somebody to define and code explicit rules for such programs to work. These are the tasks that are easy for a computer to solve but difficult or time consuming for humans. For instance, performing complex calculations, storing massive amounts of data, searching through huge databases, and so on are tasks that can be performed efficiently by a computer once the rules are defined.

Yet, there is another class of problems that can be solved intuitively by humans but are difficult to program. Problems like object identification, playing games, and so on are natural to us yet difficult to define with a set of rules. Alan Turing, in his landmark paper Computing Machinery and Intelligence (https://www.csee.umbc.edu/courses/471/papers/turing.pdf), which introduced the Turing test, discussed general purpose computers and whether they could be capable of such tasks.

This new paradigm, which embodies the thoughts about general purpose computing, is what gave rise to AI in a broader sense. This new paradigm, better termed as an ML paradigm, is one where computers or machines learn from experience (analogous to human learning) to solve tasks rather than being explicitly programmed to do so.

AI is thus an encompassing field of research, with ML and deep learning being specific subfields of study within it. AI is a general field that includes other subfields as well, which may or may not involve learning (for instance, see symbolic AI). In this book we will concentrate our time and efforts upon ML and deep learning only. The scope of artificial intelligence, machine learning, and deep learning can be visualized as follows:

A formal definition of ML, as stated by Tom Mitchell, is explained as follows.

A computer program is said to learn from experience E with respect to some task T and some performance measure P, if its performance on T, as measured by P, improves with experience E.

This definition beautifully captures the essence of what ML is in a very concise manner. Let's take an example from the real world to understand it better. Let's consider a task (T) is to identify spam emails. We may now present many examples (or experiences E) to a system about spam and non-spam emails, from which it learns rather than being explicitly programmed. The program or system may then be measured for its performance (P) on the learned task of identifying spam emails. Interesting, isn't it?

ML is thus the task of identifying patterns from training examples and applying these learned patterns (or representations) to new unseen data. ML is also sometimes termed as shallow learning because of its nature of learning single layered representations (in most cases). This brings us to the questions of what layers of representation are? and what deep learning is? We will answer these questions in the subsequent chapters. Let's have a quick overview of deep learning.

Deep learning is a subfield of ML that is concerned with learning successive meaningful representations from training examples to solve a given task. Deep learning is closely associated with artificial neural networks that consist of multiple layers stacked one after the other, which capture successive representations.

Do not worry if it was difficult to digest and understand, as mentioned, we will cover more in considerable depth in subsequent chapters.

ML has become a buzzword thanks to the amount of data we are generating and collecting along with faster compute. Let's look at ML in more depth in the following sections.