A CAD application naturally consists of several components.
The purpose of CAD, as I'm defining it, is to provide the user with a universe to build and explore. A universe of one's own, you could call it. This universe is a file, and that file is a component of a CAD application. Systems of some sort are required to enable the user to build this file, and those systems are a component of a CAD application. Also, systems are required to render the contents of the file, converting it from descriptive data into visual data. Those systems are a component of a CAD application.
The two systems, the system for building the file, and the system for rendering from it, must interact, and the systems for implementing that interaction are a component of a CAD application.
Users will want to preserve their work, and systems that facilitate that are part of a CAD application. And users will want to "share" their models, and systems that facilitate "sharing" are part of a CAD application.
