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Question 2. (10 marks) (a) Explain what is meant by a transaction. Why are transactions important units of operation in DBMS? (2 marks) (b) The consistency and reliability aspects of transactions are due to the "ACID" properties of transactions. Discuss each of these properties and how they relate to the concurrency control and recovery mechanisms. Give examples to illustrate your answer. (4 marks) (c) Describe, with examples, the types of problem that can occur in a multi-user environment when concurrent access to the database is allowed. (4 marks)