There are five primary types of content (artifacts of knowledge): facts, concepts, processes, procedures, and principles (Clark, Mayer, 2007):
Facts Specific and unique data or instance.
Concepts A class of items, words, or ideas that are known by a common name, includes multiple specific examples, shares common features. There are two types of concepts: concrete and abstract.
Processes A flow of events or activities that describe how things work rather than how to do things. There are normally two types: business processes that describe work flows and technical processes that describe how things work in equipment or nature. They can be thought of as the big picture, of how something works.
Procedures A series of step-by-step actions and decisions that result in the achievement of a task. There are two types of actions: linear and branched.
Principles Guidelines, rules, and parameters that govern. It includes not only what should be done, but also what should not be done. Principles allow one to make predictions and draw implications. Given an effect, one can infer the cause of a phenomena. Principles are the basic building blocks of causal models or theoretical models (theories).