1. A method of operating a computing device to execute a document authoring tool that forms an interactive document, the method comprising: with at least one processor: receiving a plurality of user inputs defining the interactive document, the plurality of user inputs identifying: a plurality of entities, at least a portion of the plurality of entities comprising a transformation indicating a relationship between input data and output data of the entity; and a plurality of edges, each of the edges indicating a data flow between two of the plurality of entities; and verifying that the plurality of edges interconnect the plurality of entities in an acyclic graph, wherein: the entities are of a plurality of types.