From the user's perspective, the objects in the problem domain are fairly straightforward: there are algae, fish of various types and the environment (the game board). There is also a scoreboard — a display which provides feedback telling the user the state of the game, including:
At this stage, we have done the initial analysis for Phish, and can map some of the relationships between the objects we have uncovered:
Even this simple example yields a relatively interesting diagram of the initial requirements analysis. We see the user plays the game. The game consists of a display, an environment and various life forms. The algae and fish are types of life forms and the user, by way of the game, can create fish. Each fish type has a set of rules.
This diagram is only intended to capture some of the principal relationships already understood during the requirements analysis. It is not the intention for this diagram to represent the objects in the design — those will be determined later in the process. Right now, we just want to make sure that we've understood the requirements in sufficient detail, before we begin the design in earnest.