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The SEQUAL framework is a reference model for evaluating the quality of models, the semiotic quality framework (SEQUAL) developed by John Krogstie. The SEQUAL framework is grounded in semiotics, particularly the semiotic theory of Charles W. Morris. It builds on semiotic theory and defines several quality aspects based on relationships between a model, a body of knowledge, a domain, a modeling language, and the activities of learning, taking action, and modeling.