Seminar 1

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Seminar 1
2013-04-29 12:48:28

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  1. What is the role of middleware in a distributed system?
    To enhance the distribution transparency that is missing in network operat-ing systems. In other words, middleware aims at improving the single-systemview that a distributed system should have.
  2. Explain what is meant by (distribution) transparency, and give examples ofdi erent types of transparency.
    Distribution transparency is the phenomenon by which distribution aspectsin a system are hidden from users and applications. Examples include ac-cess transparency, location transparency, migration transparency, reloca-tion transparency, replication transparency, concurrency transparency, fail-ure transparency, and persistence transparency.
  3. Why is it sometimes so hard to hide the occurrence and recovery from fail-ures in a distributed system?
    It is generally impossible to detect whether a server is actually down, or thatit is simply slow in responding. Consequently, a system may have to reportthat a service is not available, although, in fact, the server is just slow.
  4. Describe precisely what is meant by a scalable system. Scalability can beachieved by applying di erent techniques. What are these techniques?
    A system is scalable with respect to either its number of components, geo-graphical size, or number and size of administrative domains, if it can growin one or more of these dimensions without an unacceptable loss of per-formance. Scaling can be achieved through distribution, replication, andcaching.