finite automata2

A finite-state automaton (FSA) is a machine which takes, as input, a finite string of symbols from some alphabet ?. There is a finite set of states in which the machine can find itself. The state it is in before consuming any input is called the start state. Some of the states are accepting or final. If the machine ends in such a state after completely consuming an input string, the string is said to be accepted by the machine. The actual functioning of the machine is described by something called a transition function, which specifies what happens if the machine is in a particular state and looking at a particular input symbol.
• In a DFA, the next state is completely determined by the current state and the symbol being scanned, according to the transition function ?.
• In a nondeterministic finite automaton (NFA), there may be a choice of several states to transition into at each step, and may decide not to advance the read head.
• Transition diagram may have any number of edges with the same label leaving the same state. There can also be "? edges (meaning: make the transition without reading the symbol or advancing the read head).