An extensible object model enables extending the standard methods and/or properties of an extensible object for an application through an extension object proffered at run time by an extension package Information about the extension package is registered in a database when the package is installed, and the database is used to resolve references to the extended methods and/or properties upon execution of the application. In one aspect of the invention, the extension object is cached when first referenced and subsequent references to the extension while the application is executing are resolved to the cache.