1. A method performed by a computing system for evaluating one or more expressions that represent one or more characteristics of a dataflow graph that includes vertices representing data processing components connected by links representing flows of work elements between the components, the method including: receiving, by the computing system, a request to evaluate the one or more expressions that include one or more operations on one or more variables; and evaluating the one or more expressions, by the computing system, the evaluating including defining a data structure that includes one or more fields, collecting, during execution of the dataflow graph, tracking information associated with one or more components of the dataflow graph, storing values associated with the tracking information in the one or more fields, and replacing one or more variables of the one or more expressions with the values stored in the one or more fields to compute a result of evaluating the one or more expressions.