12. A system, comprising: a plurality of processing devices in data communication, wherein the processing devices are operable to perform operations comprising: for each representation of a plurality of representations of predictive models, selecting a model implementation from a plurality of model implementation for the representation, wherein each representation is associated with a respective user and comprises a description of a respective predictive model, the selection based on a status of the representation's respective user; associating each of the model implementations with a respective node in a directed graph wherein for one or more ordered pairs of nodes in the graph the prediction output of a model implementation associated with a first node in the pair serves as input to a model implementation associated with a second node in the pair; determining, from the directed graph, a subset of model implementations that can be executed in parallel based on edge dependencies in the directed graph; and causing the models in the subset of model implementations to be executed in parallel.
12. A system, comprising: a plurality of processing devices in data communication, wherein the processing devices are operable to perform operations comprising: for each representation of a plurality of representations of predictive models, selecting a model implementation from a plurality of model implementation for the representation, wherein each representation is associated with a respective user and comprises a description of a respective predictive model, the selection based on a status of the representation's respective user; associating each of the model implementations with a respective node in a directed graph wherein for one or more ordered pairs of nodes in the graph the prediction output of a model implementation associated with a first node in the pair serves as input to a model implementation associated with a second node in the pair; determining, from the directed graph, a subset of model implementations that can be executed in parallel based on edge dependencies in the directed graph; and causing the models in the subset of model implementations to be executed in parallel. 15. The system of claim 12 , the operations further comprising: selecting a computationally-intensive model implementation for the model representation based on a determination that system resources were previously used during an off-peak time of day.