Classical organisms made of cells, is a special case of a more general concept. Generalized or abstract organism can be made of the other organisms; for example an 'ant hill' can be viewed as a single organism, made of mostly of individual ants or society as an organism made of individuals. The individual units may be anorganic (robots) or exist only in a computer (artificial life). Such complex systems, which like classical organisms exhibit goal-oriented behaviour are called abstract organisms.