A tutorial sheet explained the meaning of UML class diagrams, and, using a simple example, described its semantics. Subjects were not expected to have any prior knowledge of UML, and this tutorial provided all the UML background information they required for the experimental task. A worked example demonstrated the task that the subjects were to perform, by presenting a small specification with four different diagrams, and for each diagram indicating whether it matched the given specification or not. Care was taken to ensure that neither the tutorial nor the worked example would bias the subjects towards one layout over another
