An instrumentation analysis system processes data streams by executing instructions specified using a data stream language program. A user interface allows users to specify data stream language programs. The user interface presents widgets to the user to specify various components of a data stream language program including a filter expression, an analytical function representing an aggregation or transformation, and so on. The user interface allows users to specify an expression based on results of previously specified data stream language programs. The instrumentation analysis system processes the data stream language programs specified by the user to generate a set of result data streams and plots the result data streams, for example, on a screen of a client device.