An open distributed system allows new resource sharing services such as the BLOB object in Exercise 1.7 to be added and accessed by a variety of client programs. Discuss in the context of this example, to what extent the needs of openness differ from those of heterogeneity.
What will be an ideal response?
To add the BLOB object to an existing open distributed system, the standards mentioned in the answer to
Exercise 1.7 must already have been agreed for the distributed system To list them again:
• the distributed system uses a common set of communication protocols (probably Internet protocols).
• it uses an defined standard for representing data items (to deal with heterogeneity of hardware).
• It uses a common standard for message passing operations (or for invocations).
• It uses a language independent standard for representing data structures.
But for the open distributed system the standards must have been agreed and documented before the BLOB
object was implemented. The implementors must conform to those standards. In addition, the interface to the
BLOB object must be published so that when it is added to the system, both existing and new clients will be
able to access it. The publication of the standards allows parts of the system to be implemented by different
vendors and to work together.
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For what purpose did British scientists build Colossus I?
a. word processing b. forensic analysis c. census tabulation d. cryptanalysis
Member function definitions:
a. Always require the scope resolution operator (::). b. Require the scope resolution operator only when being defined outside of the definition of their class. c. Can use the scope resolution operator anywhere, but become public functions. d. Must use the scope resolution operator in their function prototype.