The Core classes (in the classes/core directory) provide fundamentally important functions and several of the classes upon which much of the functionality of OJS 2.x is based. They are simple in and of themselves, with flexibility being provided through their extension.
Core.inc.php: Provides miscellaneous system-wide functionsDataObject.inc.php: All Model classes extend this classHandler.inc.php: All Page classes extend this classRegistry.inc.php: Provides a system-wide facility for global values, such as system startup time, to be stored and retrievedRequest.inc.php: Provides a wrapper around HTTP requests, and provides related commonly-used functionsString.inc.php: Provides locale-independent string-manipulation functions and related commonly-used functionsIn particular, the Request class (defined in classes/core/Request.inc.php) contains a number of functions to obtain information about the remote user and build responses. All URLs generated by OJS to link into itself are built using the Request::url function; likewise, all redirects into OJS are built using the Request::redirect function.