In much the way that a building is constructed through contracts, contractors, bids, materials, and labor, a computer application may be thought of in a similar light with the final product being desired information. In this section we concentrate on the four participants involved with executing a computer application: the end user, the application program, the system software, and the hardware specification file. Of course, the application program, system software, and hardware specification file are created by application programmers, system software designers, and hardware engineers, respectively. But when the contract between the end user and application program is being negotiated, it is the software entities that are participating, not the people. The only human that is directly involved is the end user. After the participants have been described, we describe in Section 4 the interactions between the four participants in terms of the three-stage contract.