Chained Hash Tables are table arrays that require a hash function to efficiently identify a particular element. A collision occurs when two or more objects map to the same array location. When this happens, the objects are chained together in the form of a linked list. An good hash function should prevent the hash value from being negative, and it should ensure that the objects being inserts span the length of the array. A hash function based only on the ASCII values of characters, for example, would be unwise.