Even before detailed design of an application, certain portions of pages will be common to most, if not all, pages. The canonical example is a "navigation bar", a collection of links and buttons used to navigate to specific pages within the application. An e-commerce site may have a shopping cart related component that can appear in many places.

In many cases, common components may need to be parameterized: the navigation bar may need a parameter to specify what pages are to appear; the shopping cart component will require a shopping cart object (the component is the view and controller, the shopping cart object is the model).

Other examples of common components are viewers and editors of common data types.

In the Virtual Library, components that make use of the external service were created. The components, BookLink and PersonLink, took as parameters the corresponding objects (Book or Person) and created links to the pages that displayed the details of that Book or Person.