Magento is a web application implementing a Front Controller pattern, and this means that most HTTP requests are routed to the index.php file in the root folder. In order to display a category, a product, or a non-catalog information page Magento parses the incoming URL to determine which modules and controllers must be engaged to process the request. When the URL rewriting is not enabled Magento URLs look like this: catalog/product/view/id/166 or catalog/category/view/id/10. These are valid URLs and they contain important information, which Magento uses to produce HTML output. Thus, catalog points to the module Mage_Catalog, product is translated into ProductControler, view – into viewAction, and the parameter id passes its value “10”. Altogether such URL generates a call to function Mage_Catalog_ProductContoller::viewAction(), which renders a details page for a product with ID 10.
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