In the design of an algorithm a programmer should not try to express it in all detail at once. Instead, the programmer should split it into major parts which can be refined in a stepwise fashion down to the elementary entities belonging to the programming language. Algorithms are thus composed of other algorithms which in their turn are either composed or elementary.
Particular composition mechanisms for the algorithms on the one hand, and the objects and types on the other hand, are termed <#1444#>control structures<#1444#> and <#1445#>data structures<#1445#>, respectively.