People can't help but use themselves?/FONT>their own life experiences?/FONT>as a point of reference for understanding the world and the experiences of others. Definitions, algorithms, and programs may also refer to themselves, but for a different purpose: to express their meaning or intention more clearly and concisely. They are then said to be recursive. Languages such as C that allow functions to call themselves are called recursive languages. When no self-reference is allowed, languages are said to be nonrecursive or iterative.
Self-reference is not without its pitfalls. You have most likely encountered the frustration of circular definitions in the dictionary, such as "Fashion pertains to style" and "Style pertains to fashion." From this you conclude that "Fashion pertains to fashion." This kind of self-reference conveys no information; it is to be avoided. "This sentence is false" is another type of self-reference to be avoided, for it tells us nothing. If true it must be false, and if false it must be true. Nevertheless, self-reference is an important technique in finding and expressing solutions to problems.
Recall that the top-down approach to problem solving entails breaking down an initial problem into smaller component problems. These components need not be related except in the sense that putting their solutions together yields a solution to the original problem. If any of these component problems is identical in structure to the initial problem, the solution is said to be recursive and the problem is said to be solved by recursion. If the solution and its components are functionally modularized, then the solution will refer to itself. Recursion is thus a special case of the top-down design methodology.
Suppose a traveler asks you, "How do I get there from here?" You might respond with a complete set of directions, but if the directions are too complex, or you are not sure, your response might be: "Go to the main street, turn left, continue for one mile, and then ask, "How do I get there from here?" This is an example of recursion. The traveler wanted directions to a destination. In solving the problem, you provided an initial small step leading toward the traveler's goal. After taking that step, the traveler will be confronted with a new version of the original problem. This new problem, while identical in form to the original, involves a new starting location closer to the destination.
Cursing is often used to belittle a problem; recursing has the same effect! Recursion, when appropriate, can give relatively easy-to-understand and concise descriptions for complex tasks. Still, care must be taken in its use, or else efficiency of storage and execution time will be sacrificed.