You do not have to literally specify one of these types when you create a mapping. Rather any mapping that you create can be described as belonging to one of these four types.
The four types of mappings are:
A one-sided mapping is a mapping that stores literal data (such as the literal number 1024, the literal string '1000 Main Street', or a time-date stamp) into a target element. A one-sided mapping does not read data from a source element.
Examples of transforms that create one-sided mappings are: Assign, Clear, Current Timestamp.
A one-to-one mapping is a mapping that reads an input value from a single source element, operates on the input value with a transform (sometimes using additional immediate input values), obtains a result, and stores a single output value into a target element.
Examples of transforms that create one-sided mappings are: SIN, Cast, Move, Lower Case, Substring
A many-to-one mapping is a mapping that reads input values from multiple source elements, operates on the input data with a transform, obtains a result, and stores a single output value into a target element.
Examples of transforms that create one-sided mappings are: Add, Concatenate, Divide.
(See Source elements, target elements.)
Examples of transforms that create one-sided mappings are: Move.