Extract-Transform-Load (ETL) workflows are data centric workflows responsible for transferring, cleaning, and loading data from their respective sources to the warehouse. Previous research has identified graph-based techniques that construct the blueprints for the structure of such workflows. In this paper, we extend existing results by explicitly incorporating the internal semantics of each activity in the workflow graph. Apart from the value that blueprints have per se, we exploit our modeling to introduce rigorous techniques for the measurement of ETL workflows. To this end, we build upon an existing formal framework for software quality metrics and formally prove how our quality measures fit within this framework.