The first step in defining an annotation or measurement is to identify what data is to use. Since many data are typically available, the data source is identified by choosing a sequence of values for up to three primary parameters (Qualifier 1, Qualifier 2, and Qualifier 3) and often a set of secondary parameters.
The majority of the time the data source is taken directly from results of a simulation (one exception to this is that a measurement can be made on an annotation). Most simulations will produce one or more datasets per Adaptive Mesh Refinement (AMR) iteration. Each dataset contains within it a number of data items - typically meshes, fields, particles, and tables. In this case, Qualifier 1 is used to choose the simulation, Qualifier 2 is used to choose the AMR iteration. Qualifier 3, and subsequent secondary parameters, further narrow down the data to unique data.