Specification

f(x) -> g(x')

Description

The mapper pattern is the transparent redirection of a request for a given URI to an intermediary accessor or script - called the mapper function. The mapper interprets the requested URI based upon a mapping rule and reissues a sub-request to another URI specified or computed from the mapping rule. The response from the sub-request is transparently returned as the response from the mapper to the original URI request.

Generally mapping rules are declaratively defined. However it is equally possible to write a mapper function which algorithmically computes the sub-request URI from the original request.

Usage

This pattern occurs frequently and is used to provide indirection between a public URI interface and the implementation of that service.

The mapper accessor is an embodiment of this pattern - this accessor may be used to delegate the implementation of a module's public interface. It is also frequently used for mapping from a public URL web-address space to an implementing URI address space in XRL-based web applications.