A database conceptual schema serves as a communication medium between professional analysts/designers and users who wish to comprehend and validate the conceptual schema. The conceptual schema is usually presented in a diagrammatic form that follows a specific semantic data model. The extended entity-relationship (EER) model is one of the most commonly used models, but being “threatened” by the object oriented (OO) approach, which penetrates into the areas of systems analysis and design, as well as data modeling. The issue of which of the two data models is better for modeling reality and is easier to comprehend is still an open question. Our response to this question was to conduct a controlled experiment in which two groups of users, each trained to use one of the models, were tested for the comprehension of equivalent schema diagrams. Comprehension was measured by the number of correct answers to questions that addressed different constructs of the models. The results of the experiment reveal that there is no significant difference in comprehension of facts dealing with attributes of entities or objects, binary-relationships and two relationships, but those dealing with ternary-relationships are significantly easier to comprehend with the EER model. Comprehension of other, unclassified facts, however, is easier with the OO model. We propose a special symbol for objects representing ternary and higher order relationships in order to overcome the weakness of OO diagrams.