The term Programming by example (PbE) or Programming by demonstration (PbD) appeared in software development research as early as the mid 1980s to define a way to define a sequence of operations without having to learn a programming language. The usual distinction in literature between these terms is that in Programming by example the user gives a prototypical product of the computer execution, such as a row in the desired results of a query; while in Programming by demonstration the user performs a sequence of actions that the computer must repeat, generalizing it to be used in different data sets.
These two terms were first undifferentiated, but Programming by example then tended to be mostly adopted by software development researchers while Programming by Demonstration tended to be adopted by robotics researchers.
The PbD paradigm is first attractive to the robotics industry due to the costs involved in the development and maintenance of robot programs. In this field, the operator often has implicit knowledge on the task to achieve (he/she knows how to do it), but does not have usually the programming skills (or the time) required to reconfigure the robot. Demonstrating how to achieve the task through examples thus allows to learn the skill without explicitly programming each detail.
The first PbD strategies proposed in robotics were based on teach-in, guiding or play-back methods that consisted basically in moving the robot (through a dedicated interface or manually) through a set of relevant configurations that the robot should adopt sequentially (position, orientation, state of the gripper). The method was then progressively ameliorated by focusing principally on the teleoperation control and by using different interfaces such as vision.
However, these PbD methods still used direct repetition, which was useful in industry only when conceiving an assembly line using exactly the same product components. To apply this concept to products with different variants or to apply the programs to new robots, the generalization issue became a crucial point. To address this issue, the first attempts at generalizing the skill were mainly based on the help of the user through queries about the user's intentions. Then, different levels of abstractions were proposed to resolve the generalization issue, basically dichotomized in learning methods at a symbolic level or at a trajectory level.
The development of humanoid robots naturally brought a growing interest in robot programming by demonstration. As a humanoid robot is supposed by its nature to adapt to new environments, not only the human appearance is important but the algorithms used for its control require flexibility and versatility. Due to the continuously changing environments and to the huge varieties of tasks that a robot is expected to perform, the robot requires the ability to continuously learn new skills and adapt the existing skills to new contexts.
Research in PbD also progressively departed from its original purely engineering perspective to adopt an interdisciplinary approach, taking insights from neuroscience and social sciences to emulate the process of imitation in humans and animals. With the increasing consideration of this body of work in robotics, the notion of Robot programming by demonstration (also known as RPD or RbD) was also progressively replaced by the more biological label of Learning by imitation.