1. A computer-implemented system for processing time series data that is indicative of a data generation activity occurring over a period of time, comprising: one or more processors; a computer-readable storage medium containing instructions configured to cause the one or more processors to perform operations including: storing characteristics that define a time series model, wherein the characteristics of the time series model are stored in a model specification hierarchical data structure; and storing characteristics that define a fitted time series model, wherein the characteristics of the fitted time series model are stored in a fitted model hierarchical data structure, and defined through an application of the time series model to the time series data.