Tree, River, City Lights – Part I

By Failbetter, May 11, 2011 · Tagged with ,

[This is one in an intermittent series of posts about internal FBG terminology. Partly because we use these terms in the wider world sometimes, partly because it might have more general implications. This post is also about my ambivalent relationship with the tree as a model for how to think about interactive stories.]

Trees (directed graphs, flow charts, all their cousins) are a natural way to think about stories. You make a choice, you make another choice, you make another choice… you reach an ending. You can trace your path back clearly from your final ending to the beginning. If you’ve ever tried to conceptualise or visualise a story from a height, you probably drew a tree.

But only a minority of interactive stories (eg hypertext narrative,  the classic choose-your-own-adventure style of gamebook without the refinements of later gamebooks) are really just tree stories. Partly this is the notorious issue of combinatorial explosion: trees can’t just keep branching indefinitely for the length of the story! So we merge some branches back into others (which only feels like a cheat when you notice), or we create some sort of state (Stamina, Dark Side Points, inventory items, … Connected: the Duchess) that decisions can affect. Even quite tree-ish narratives are rarely pure tree. But partly it’s because most interactive narratives are different in an important respect: you have a choice about when you make choices. 

This is the fundamental property of a river story. In a pure tree, each choice is followed by a predetermined next. In a river, you have some degree of control over when you make what choice. It might mean that you’re navigating a textual space where the use of verbs has some geographic texture, as in traditional IF, or exploring a map full of canned encounters, as in a classic CRPG. It might mean that you’re picking from a menu of storylets, as in Echo Bazaar.

This fundamental property often gets called ‘non-linearity’ in game reviews, and that often leads to disappointment. When we call something non-linear we suggest that it’s not a story in the traditional sense, because a story has a beginning, a middle and an end. It is very hard to make satisfying stories, interactive or not, that don’t have a definite beginning, middle, and end. It’s arguably not impossible: just difficult and not necessarily worth the effort.

The river, then, has a beginning, middle and end. The end may be multiple endings, but you’re basically being funnelled through a similar landscape to everyone else on the river. That’s all right. Your experience can be fundamentally different, just as the experience of a hundred people travelling the same ten miles of road can have be different, depending on who tripped over what donkey or who met their lover when or who was robbed and who hid behind a boulder. And your internal experience may be much more radically different, especially where the story is something that allows for interpretation.

This is a significant tension at the heart of interactive stories. A story is a series of things happening in a particular order: it’s the order that makes it a story. But in a riverine interactive story, you choose what order things happen in! Tree stories resolve this by not allowing you to decide the order. River stories keep their beginning, middle and end, and they also keep floes or islands of relative inflexibility in the middle.

Of course I’m conflating different kinds of event here, I know: ‘a wandering monkey punched me for five hit points of damage’, ‘I remember a monkey punching me in my youth’, ‘my beloved monkey punched me, ending our friendship forever’, ‘the inevitable monkey punch occurred in the pantry rather than the parlour’, and so forth. Next time I’ll talk about that, about internal experiences, and about city lights.


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Tree, River, City Lights – Part II · Failbetter Games May 12, 11:39am

[…] follows on from the post in which I explained, to my own satisfaction at least, how trees / graphs aren’t always the best way to manage […]

Lily May 16, 2:32am

(I've really got to decide which name -Kast/Lily- to use around here) Interesting exploration of the idea there. The river analogy is particularly apt - sometimes you reach a lake, sometimes a diversion. You could also think about grander stories as a fishing net design - multiple start points each running to different combinations of the total available stage two points, which again lead to different combinations of the total available stage three points and so on until you reach multiple end points. A reader/player can enter the story through many different points and zig-zag their way through the story world to end up at any of the available endings. The path between beginning and end may be simple or convoluted but each step would flow logically. Weave enough rivers together, for example EB story arcs with the same Contacts, ability or items and this is the kind of design you might come up with.

James Walker May 13, 9:47pm

I'm loving the way you've allowed us to redo the entire 'What The Thunder Said', modifying it enough to be novel yet still keeping it familiar...sort of like a new meal in a favourite restaurant.

Joseph Humfrey May 12, 5:57pm

Interesting. For a while I've been thinking about how a story could be represented with a more analogue rather than digital approach. Right now we're definitely thinking in terms of reading a piece of text, performing an atomic action or choice, the world changing state and reading the next piece of text. A tree is composed of nodes and branches. But when you say "river" I imagine a bit of breadth and some kind of continuous range of possibilities. One advantage that most AAA video games have is that they're inherantly analogue. You can walk here and there, do certain actions in particular ways you choose, with only a few of the actions being truly simple and clean-cut. I guess that's simply something that can be produced when you have a visual rather than textual output - easy simulation and variability. You can easily stand five metres to the left within a room without thinking about it. Is it possible to create any kind of parrallel with interactive text? And is there a way to do it in a way that isn't overly cumbersome? (By the way Kdansky, I was going to say DAG too, but actually it's not necessarily acyclic! So it's just a directed graph I guess...)

Kdansky May 12, 3:26pm

The mathematical term instead of tree would be DAG, directed acyclic graph. I found EBZ inspiring enough to actually write some code influenced heavily by it.

Alexis May 12, 1:27am

Cheers! We talk about 'weather' qualities: qualities that change only occasionally and have consequences all over. A Person of Importance is a bit like that: it unlocks second-part content and also locks out some early content, like easy menace reduction. For another work in progress project for a client, we have more explicit 'Episode' qualities with several possible storylets that serve as points of transition, each unlocked by one of several different combos of storylet. We do have a clear arc and ending planned for EBZ, though it keeps expanding sideways.

Jon Ingold May 12, 1:06am

I love it when you get really clear, simple articles about interactive structures, that manage to avoid too much "of course" and "clearly". I've found ENZ's "river" concept to be its stand-out feature, that no-one else seems to be using as effectively (even in the big RPGs, who are close to something similar but always seen to end up making trees anyway.) The only issue I have with it is a pacing one: how do you go about making your third act? In the case of EBZ, there's been definite expansion in scope, but do you see it ever ending? Jon