29 01 16

Page 1

Dipartimento di Elettronica, Informazione e Bioingegneria Politecnico di Milano Prof. Elisabetta Di Nitto, Raffaela Mirandola 20133 Milano (Italia) Piazza Leonardo da Vinci, 32 Tel. (39) 02-­2399.3400 Fax (39) 02-­2399.3411 Software Engineering II January 29 2016 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. The use of any electronic apparatus (computer, cell phone, camera, etc.) is strictly forbidden. 4. You cannot keep a copy of the exam w hen you leave the room . 2 Question 1 Alloy (7 points) We want to model the behavior of a component that migrates data from a source storage to a destination storage. Data is divided in chunks that are migrated independently from each other and possibly in parallel to improve performance (independence and parallelization of chunk migration is not to be handled in this exercise). Each chunk can be in one of the following states: ready to be migrated, under migration, migrated. Of course, the whole migration ends when all chunks in a data set are in the migrated state. Queries are related to specific chunks of data in a one-to-many relation. These queries can be potentially executed on the chunks when these last ones are still to be migrated or when they are migrated, while they have to be postponed when one of the involved chunks is under migration. Define an Alloy model for the above problem. Focus on the definition of the signatures and facts that describe the constraints described above. Solution sig Storage {} sig Data {} abstract sig ChunkStatus {} one sig Ready extends ChunkStatus {} one sig UnderMigration extends ChunkStatus {} one sig Migrated extends ChunkStatus {}…