This UML Sequence Diagram for Library Management System is critical in using case-driven object-oriented (OO) software engineering. They are OO variants of the ITU-T standard language Message Sequence Chart (MSC), widely used in telecommunications. Harmonization would benefit both notations. On the one hand, a more formal and powerful reminder for Sequence Diagrams may emerge. MSC's application area, on the other hand, could be significantly expanded.
