Database Concepts Essay

771 WordsOct 11, 20114 Pages
Name: Troy Dowling Student No: s3338219 Assignment 2 Q1. Briefly explain each of the following database terms. Use no more than 2 -3 lines for each term. 1. DBMS: A (DBMS) Database Management System is a collection of software programs that allow the creation and maintenance of databases. A DBMS allows the company to manage large amounts of data easily and effectively. A DBMS is used by a database administrator (DBAs). 2. Update Anomaly: A update anomaly is when one tuple is updated but the same information in another tuple is not changed. A relation can be designed so this can not happen. 3. Alias (referring to tables in SQL queries): An Alias (AS) can change the title of the column in the table produced using SQL. e.g. To use TITLE for a header of the column instead of MOVIE. 4. Weak Entity: A weak entity allows the creation of same named relations in different tuples. This allows multiple entries to have the same name but different relations. Q2 Q3A A = ITEM_NO, B = ITEM_DESCRIPTION C = CUST_NO D = CUST_CONTACT E = LOANDURATION F =SUPPLIERNAME G = DISCOUNT A: if (ac > e) and (e > g) then using transitivity replace (ac > e with ac > e, g) and remove (e > g) if (ac > e, g) and (c > d) then using augmentation and transitivity replace (ac > e, g with ac > e, g, d) remove (c > d) then make RHS singletons the remaining FD are: ac > e ac > d ac > g a>b a>f using FD on LHS to determine key for relation: FD = {ac > e ac > d ac > g a>b a>f} a+ = a, b, f ac+ = a, c, b, f, d, e, g = SUPERKEY {ace} = {ITEM_NO, CUST_NO} {ITEM_NO, CUST_NO} is the superkey because without these attributes you can not know any of the other attributes. B: R ( a b c d e f g) the FD (ac > d) is in BCNF, but the FD (a > b) is not as the LHS does not contain the superkey. c: BCNF violation a > b {a+} = a, b, f R1 ( a* b f ) FD's = a > b, a > f = BCNF R2 ( a

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