Comments on: EP 7.2: Universe

By: Michael Mateas

Michael Mateas — Sun, 17 Aug 2008 23:49:45 +0000

Universe explicitly employs a rhetoric of authorship (the content of plot fragments depends on the story the author wants to tell, and are otherwise atheoretical), while Tale-Spin does use the rhetorical language of a theory of intelligent action. But of course, the truth is that Tale-Spin characters are just as “authored” as Universe plot fragments.

By: Noah Wardrip-Fruin

Noah Wardrip-Fruin — Sat, 16 Aug 2008 22:53:39 +0000

Maybe there’s not enough emphasis, in the last sentence of this paragraph, on the “doesn’t sound” phrase. I mean to say that Tale-Spin‘s operations are presented using language that implies a simulation of intelligent action in the world, while Universe employs a less impressive-sounding rhetoric.

By: Noah Wardrip-Fruin

Noah Wardrip-Fruin — Sat, 16 Aug 2008 22:49:12 +0000

I read the idea of a “goal with no unmet preconditions” relatively simply. For example, if churning lovers is a goal, there must be lovers to churn before it can be pursued.

But I agree it would be great to get an expansion of the information on things like how Universe “maintains a precedence graph that records how the various pending author goals and plot fragments relate to each other and to events that have been told already” (and so on) in the 1985 paper. I don’t have more information (that I recall) but perhaps we might ask Lebowitz.

By: Noah Wardrip-Fruin

Noah Wardrip-Fruin — Sat, 16 Aug 2008 22:20:16 +0000

I think we get down to a distinction that may seem a little fine here — but I think it’s also a crucial distinction. It’s one thing to try to simulate what we think real authors do and it’s another to organize a story generation system to that it has an “author” level (without any commitment to whether what it does has any particular relationship to what human authors do).

However, while I think this distinction is important, and I think Universe is an example of the latter (while Minstrel is an example of the former) it is true that Lebowitz’s writing creates some confusion. For example, while no cognitive science model of creativity is given as the basis of the system’s design, Lebowitz still gestures toward the cognitivist view of AI, writing in one paper that a goal of Universe is “to better understand the cognitive processes human authors use in generating stories” (1984, 172) and in another that we “can expect research into extended story generation to … give us insight into the creative mechanism” (1985, 484). Exactly how this will take place is never explained.

I’ve added a footnote to this effect.

By: michael

michael — Tue, 13 May 2008 19:30:07 +0000

Incidentally, Tale-Spin is sequencing character plans to accomplish character goals. At a high level, Tale-Spin and Universe are similar: they both sequence plans to achieve goals, where plans involve recursive subgoal pursuit. This is the basic loop for reactive planning (minus reactive conditions) as well. So it’s not clear to me that Tale-Spin seems more impressive than Universe.

By: michael

michael — Tue, 13 May 2008 19:29:37 +0000

Liebowitz proposes using a modified form of explanation-based learning to generalize the constraints in plot fragments. He gives one example (not clear if hand generated or not) of an explanation for the forced marriage plot fragment, and how the explanation can be used to generalize the constraints (standard EBL stuff). EBL of course requires a domain theory, which goes beyond simply authoring plot fragments; the author would have to provide a logical theory for how plot fragments achieve their author goals. Liebowitz does say that at the time of writing, his modified EBL is working. This is an example of something deeper than sequencing plot fragments.

By: michael

michael — Tue, 13 May 2008 19:22:02 +0000

I’ve never fully understood what is meant in “choosing goals that have no unmet preconditions”. Typically preconditions are associated with plans rather than goals. It sounds like there’s some sort of precedence relationship maintained over goals, but it isn’t really described in his publications. In your researches, did you ever get more clarity on this?

By: michael

michael — Tue, 13 May 2008 18:37:46 +0000

While Universe doesn’t provide an explicit cognitive model, I would still classify it as an author modeling system. Unlike Tale-Spin, which models the goals of characters and their effect on the world (character and world modeling), or story grammars, which directly model story structure, Universe models authorial goals (e.g. churn the romantic lives of two characters) and plans for achieving authorial goals. I think this qualifies it as an author modeling system, though it is not as deep a model as Minstrel.

By: noah

noah — Mon, 10 Mar 2008 16:30:34 +0000

Andrew, I’m very happy your thoughts are running in that direction, at this point in the book. As it happens, the very next chapter is called “The SimCity Effect” and tries to get at some of these issues, though from a slightly different direction. In the next chapter I focus mostly on how sandbox games can be a satisfying way of interacting with human characters because the representation on the surface maps well to an interesting model below. But the surface experience isn’t what many people want for fiction. So then I talk about how projects like Oz, Improv, and Facade can help us think about the relationship between surface appearance and underlying model in something more like an enacted fiction than a sandbox. But it’s actually only in my discussion of Petz (also in the next chapter) that I come close to grappling with how we experience something like fiction in a sandbox. Going further might be a good thing for the conclusion, which I’m planning to use to address issues that come up in the two reviews (blog-based and blind).

By: noah

noah — Mon, 10 Mar 2008 16:22:34 +0000

Thanks for the catch!

By: andrew

andrew — Thu, 06 Mar 2008 21:43:43 +0000

As an aside... The Facade architecture certainly falls in this camp. While we believe it is an expressive architecture for at least simplistic story generation (one of the requirements for high agency — agency being the primary design goal of the project), admittedly it's not been demonstrated convincingly, since the only story we've built with it to date only has 27 high-level beats (plot fragments, each able to express its core content with some variation), plus ~20 smaller narrative progressions than can mix in to the beats. I'm curious, will you be doing a section at some point on "sandbox games", e.g. The Sims or Grand Theft Auto, in regard to their story generation capabilities? (Since neither project has releaesd much technical detail about their implementation, perhaps you wouldn't be able to, even if you wanted to.) I wonder, where would you draw the line between story "emergence" from sandbox style games (e.g., the types of emergent narrative fragments that I reported from Petz and Babyz), and story "generation"? Is paragraph 21 here essentially your answer? Meaning, "emergent" story falls out of a slightly flexible system, and "generated" story from a highly flexible one?

By: Richard Evans

Richard Evans — Wed, 05 Mar 2008 20:33:57 +0000

There is a minor typo in “This is plot fragment is then made part of the story”…