A framework's URL mapping facility is the mechanism by which the framework interprets URLs.
The frameworks match the provided URLs against pre-determined patterns using regular expressions, or use URL rewriting to translate the provided URL into one that the underlying engine will recognize. Another technique is that of graph traversal, where a URL is decomposed in steps that traverse an object graph (of models and views).
A URL mapping system that uses pattern matching or URL rewriting allows more "SEO friendly URLs" to be used, increasing the simplicity of the site and allowing for better indexing by search engines. This makes the URL easier for people to read and hand write, and provides search engines with better information about the structural layout of the site. A graph traversal approach also tends to result in the creation of SEO friendly URLs.
