sol-98-99 - CIS209 - Exam paper 1998/1999 - version 1.1...

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CIS209 - Exam paper 1998/1999 - version 1.1 (23/02/99) Marian Ursu Part A Attempt four of the following six problems (estimated time 20 minutes) Total marks = 12 Problem 1 . Explain briefly, in one or two sentences, three advantages of your choice, of the database approach to software systems development. Solution: data independence reduce redundancy avoid inconsistency shared data maintain integrity apply security restrictions enforce standards balance conflicting requirements improve data accessibility improve IS’s maintenance Marking: 1 mark for each correct description (not more than 3); if other advantages are correctly identified, mark accordingly. TOTAL 3 marks. Problem 2 . Describe the three levels of the ANSI / SPARC architecture of a DBMS. Solution external level: represents the user’s view of the DB; includes only the relevant information to the use; different views might have different representations of the same data; views might include derived data; conceptual level: represents the logical structure of the DB and also the intermediate level that provides data independence ; contains the entities, their attributes and the relationships between them together with the set of constraints on them; can be viewed as the common denominator of the whole set of views; any view should be derivable from it; internal level: subsumes the physical representation of data; at this level the physical data structures and the files organisation are defined; the interface between the internal level and the Os is not clearly defined. Marking: 1 mark for the correct description of each level. TOTAL 3 marks. Problem 3 . Define and point out the difference between the intension and the extension of a database (illustrate with an example). Solution 1
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CIS209 - Exam paper 1998/1999 - version 1.1 (23/02/99) Marian Ursu the intension of the DB represents the description of the DB, the DB’s schema; the extension of the DB is an instance of the DB at a particular moment in time; represents the raw data; the intension does not change that often as opposed to the extension. Marking: 1 mark for a), b) and c). TOTAL 3 marks. Problem 4 . Explain, based on a diagrammatic representation, two possible architectures for database systems. Solution client server architecture + diagram; distributed database systems + diagram. Marking: 1.5 marks for the correct description of each approach. TOTAL 3 marks. Problem 5 . Define the optimiser in the context of a relational DBMS? Solution a) relational operators are set level operators; b) they describe the result (i.e. the “what”), but do not specify how to be computed (i.e. the “how”); 2 client machines server machine database communication network server clien server clien server client server client server client server client server client communication network
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CIS209 - Exam paper 1998/1999 - version 1.1 (23/02/99) Marian Ursu c) therefore the DBMS must have a module - the optimiser - that decides how a query is to be
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This note was uploaded on 05/13/2010 for the course COMPRO CS401 taught by Professor Just during the Spring '10 term at Maharishi.

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sol-98-99 - CIS209 - Exam paper 1998/1999 - version 1.1...

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