A map is the definition of a transformation between two structures. A map can have one input structure and one output structure, and its elements correspond exactly to the elements associated with the structures of the map. A single map can process any number of input or output documents using the explicit document Input/Output mechanism.
Certain maps may have only an input structure, such as when a map is used for document validation.
The map contains the expressions that are used to create the output document and validate the input document. These expressions generate the value of each output element, define the rules for handling looping, define the rules for input element validation, and can constrain the creation/reading of output/input elements.
Maps can inherit from other maps, allowing you to create a base map that defines typical transformations between two types of documents and then customize this map without duplicating all of the transformations in the base map.
Maps that provide for expressions to translate an input to an output structure are called standard maps. There are other special purpose maps that perform functions other than translation. For example, an XSLT Report Map can run an XSLT script processing data from an input structure.