An abstract data type storing items, or values. A value is accessed by an associated key. Basic operations are new, insert, find and delete. Formal Definition: The operations new(), insert(k, v, D), and find(k, D) may be defined with axiomatic semantics as follows.

1. new() returns a dictionary
2. find(k, insert(k, v, D)) = v
3. find(k, insert(j, v, D)) = find(k, D) if k ≠ j