354.DesignTheory

354.DesignTheory - DatabaseSystemsI DesignTheory...

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CMPT 354, Simon Fraser University, Fall 2008, Martin Ester  1 Database Systems I  Design Theory for Relational Databases
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CMPT 354, Simon Fraser University, Fall 2008, Martin Ester  2 Introduction Typically, the first database design uses a high-level database  model such as the ER model. This model is then translated  into a relational schema. Sometimes a relational database schema is developed directly  without going through the high-level design. Either way, the initial relational schema has room for  improvement, in particular by  eliminating redundancy . Redundancies lead to undesirable update and deletion  anomalies . Relational database design theory introduces various  normal  forms  of a schema that avoid various types of redundancies  and algorithms to convert a relational schema into these  normal forms.
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CMPT 354, Simon Fraser University, Fall 2008, Martin Ester  3 Functional Dependency Normal forms are based on the concept of functional  dependencies between sets of attributes. A   functional dependency  ( FD ) X   is an assertion  about a relation  R   that whenever two tuples of  R   agree  on all the attributes of set  X , then they must also agree on  all attributes in set  Y . We say “ X   Y   holds in  R .” Convention: …,  X Y Z   represent sets of attributes of  relation  R .  A B C ,… represent single attributes of  R . Convention: no parentheses to denote sets of attributes,  just  ABC , rather than { A , B , }. A FD  X   is called   trivial   if              . X Y
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CMPT 354, Simon Fraser University, Fall 2008, Martin Ester  4 Splitting / Combining Rule X A 1 A 2 A n   holds for  R   if and only if each of  X A 1 X A 2 ,…,  X A n   hold for  R . Example: The FD  A BC   is equivalent to the two FDs  A  and  A C . This rule can be used to  split  a FD into multiple ones with  singleton right sides or to  combine  multiple singleton right  side FDs into one FD. There is no splitting /combining rule for left sides. We’ll generally express FDs with  singleton   right   sides .
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CMPT 354, Simon Fraser University, Fall 2008, Martin Ester  5 Functional Dependency Consider the relation Movies1    (title, year, length, genre, studioName, starName). title year   length genre studioName  holds, assuming that there are not two movies with the  same title in the same year. title year 
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This note was uploaded on 10/07/2009 for the course CS 12601 taught by Professor Kewang during the Spring '09 term at Simon Fraser.

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354.DesignTheory - DatabaseSystemsI DesignTheory...

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