Hash Tables Parallel and Sequential Data

More formally the idea of hashing is to approximate a random function h : α→ β from a source (or universe) set U of type α to a destination set of type β . Most often the source set is significantly larger than the destination set, so the function not only chops and mixes but also reduces. In fact the source set might have infinite size, such as all character strings, while the destination set always has finite size. Also the source set might consist of complicated elements, such as the set of all directed graphs, while the destination are typically the integers in some fixed range. Hash functions are therefore many to one functions.