y one, this structure takes small groups of people and uses the same underlying structure to give them experiences that are parallel but not identical. Different small groups may have different experiences, and their experiences cannot affect each other, but within each group the players experience the story together. In the same way that a theater script supports many simultaneous performances that do not affect each other, each instance draws from the same script but does not affect any other actual story-tellings.
             For example, games such as Starcraft adopt this model. When playing online, players form groups using a chat server to connect with each other. Each group that forms then initiates an instance of the game, choosing a level or map from a series of pre-created choices. Within each group, members share a single experience: for example, the players can send their armies against each other and compete for the same resources. However, they cannot affect anything done by other groups, even ones using the same map or level.
             A small-group, parallel-structure model has several properties that make it more adaptable to interactive narrative than the others. One has to do with group size. The principles of shared authorship and mental schemata together suggest that users of this kind of story system have to have some knowledge of the others who are also in their group. Without familiarity, users can't form mental models of how they relate to the others in the group. It also means that they cannot effectively collaborate with everyone who is present. If the group is too large, familiarity suffers, because humans are only capable of maintaining around twelve different relationships at once. And, of course, if the group is too small then shared authorship becomes impossible. Small-gro
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