This package is for describing a microarray experiment as a unit. Note two parallel branches on the diagram. On the right-hand side we have experiment blueprint information - experiment design and one or more experimental factors that are changed in the course of the experiment to explore whether and how gene expression  levels change (e.g., time or drug concentration). On the left-hand side there is experiment execution information. An experiment consists of one or more bioassays (experiment steps), and each bioassay can test for gene expression with one or more experimental factor values fixed (e.g., time = 30min, drug concentration = 15ug/ml).