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Dipartimento di Elettronica, Informazione e Bioingegneria Politecnico di Milano Prof. Elisabetta Di Nitto, Luca Mottola 20133 Milano (Italia) Piazza Leonardo da Vinci, 32 Tel. (39) 02-­2399.3400 Fax (39) 02-­2399.3411 Software Engineering II June 28, 2017 Last Name First Name Id number (Matricola) Note 1. The exam is not valid if you don’t fill in the above data. 2. Write your answers on these pages. Extra sheets will be ignored. You may use a pencil. 3. Incomprehensible hand-­writing is equivalent to not providing an answer. 4. The use of any electronic apparatus (computer, cell phone, camera, etc.) is strictly forbidden. 5. You cannot keep a copy of the exam w hen you leave the room . 2 Question 1 Alloy (7 points) Observe the following figure. It describes a communication system composed of an overlay network linking nodes A and E. This overlay is a virtual network built on top of an underlay network. In the figure, the underlay network is composed of four nodes (a, b, d, and e) and link L exploits the links between a, b, d and e in the underlay network to ensure that A and E can communicate. Consider the following Alloy signatures: sig Network {uses: lone Network}{this not in uses} sig Node { belongsTo: Network, isLinkedTo: some Node, isAttachedTo: lone Node }{this not in isAttachedTo and this not in isLinkedTo} A) Explain the meaning of these signatures with respect to the figure above and indicate which elements in the figure are not explicitly modeled by the two signatures. B) Write facts to model the following constraints: • Linked nodes have to be in the same network • A node belonging to a certain network can only be attached to nodes of the corresponding underlay network • If a network is an overlay one, then there should not be nodes in this network that are…