There's one particular dialog that I want to write out here, since it illustrates an aspect of needs based agents that I was talking about. It is from the first series, episode 10, "Breakdown". It's a dialog between Blake and Zen, with a surprised remark from the technical genius, Avon, in between.
--- --- --- --- --- --- ---For a visual, here's an image of Blake talking to Zen.
Blake: Zen. Set navigation computers for direct route to space laboratory XK72. Speed Standard by Six.
Avon: You CANNOT reject a direct command!
Blake: Justify that rejection, please.
Zen: Your command reduces to an order to self-destruct. This runs counter to Prime Directive.
Blake gives Zen a command. Zen has command over all computers of the ship, it is the task manager. Blake tells Zen to delegate the command to the navigation computers of the ship.
Zen rejects. Note that rejection is a higher order function of a system. Most computers just do as they are told. Not Zen. This surprises Avon, who calls out that it is impossible for a computer to reject a command. To Avon Zen is "just a computer". But Zen is a needs based agent.
Blake asks Zen to justify the rejection. This is an introspective request. It asks Zen to inspect its own prior reasoning as an intelligent agent.
Zen explains its reasoning efficiently. He says that the command, which includes going through an part of space of which it is only known that it is extremely dangerous (it later appears to be some sort of vortex) may very likely destruct the ship. Zen checks its projected actions with its directives (in which I see the concept of needs). It finds that it runs counter to its Prime Directive (which is probably to stay alive). From this it rejects the command.
As Blake and his crew manually override Zen and continue to go through this part of space, Zen shuts down all of its functions. It refuses to cooperate. If Zen was more like HAL (in 2001, a space odyssey), it would have actively tried to counteract the actions of the humans.
Note that in Star Trek there's also a Prime Directive. There it is a guiding principle for space explorers not to interfere with alien civilizations. I consider both Zen's Prime Directive and that of Star Trek to be needs.