7-fd - CS273 - Data and Knowledge Bases Xifeng Y Xif Yan...

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CS273 - Data and Knowledge Bases Xifeng Yan Computer Science niversity of California at Santa Barbara University of California at Santa Barbara
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Department of Computer Science Homework 1 will be posted online in the lecture directory tomorrow (Oct 7, 2011). Due day: Oct 25, 2011 before class. You need to print out your answer and hand in before lass. class. CS273: Data and Knowledge Bases | University of California at Santa Barbara 2
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Department of Computer Science R is Not Enough! ER is Not Enough! The generated schemas are Not guaranteed to be “good”. The “goodness” of the schemas is not clearly defined It is an art. Is it possible to write a program that automatically generate good schemas? We will discuss the concepts/algorithms that generate relational schemas that guarantee to have some good properties. CS273: Data and Knowledge Bases | University of California at Santa Barbara 3 slides by courtesy of Y. Chen with modifications
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Department of Computer Science Outline Properties of Relational DB design (intuition) Functional Dependencies Definition Inference Attribute closure & Minimal cover Decomposition Properties (formal) No repetition of information Lossless-join Dependency preservation Normal Forms Decomposition Algorithms CS273: Data and Knowledge Bases | University of California at Santa Barbara 4
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Department of Computer Science Relational Database Design Goal: Generate a set of relation schemas that allow us to store information without unnecessary redundancy, yet allows us to retrieve information easily. y Undesirable Properties Repetition of information ability present ertain formation Inability to represent certain information Loss of information Desirable Properties No Repetition of Information (Normal Forms) Dependency Preservation Lossless-join Decomposition CS273: Data and Knowledge Bases | University of California at Santa Barbara 5
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Department of Computer Science Undesirable Properties (I) suppliers(SNAME, SADDR, ITEM, PRICE) he address of the supplier is repeated for each item The address of the supplier is repeated for each item supplied: wasted space very tuple for a supplier must be updated when every tuple for a supplier must be updated when there is an address change Repetition of information CS273: Data and Knowledge Bases | University of California at Santa Barbara 6
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Department of Computer Science Undesirable Properties (II) suppliers(SNAME, SADDR, ITEM , PRICE) Insertion: we can't record an address for a supplier if that supplier does not currently supply at least one item. Deletion: all the items supplied by one supplier are deleted if all the items supplied by one supplier are deleted, we lose the address.
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7-fd - CS273 - Data and Knowledge Bases Xifeng Y Xif Yan...

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