Week 5 (Wednesday and Friday)

Week 5 (Wednesday and Friday) - 8/3/2009 1 Normalization...

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Unformatted text preview: 8/3/2009 1 Normalization Normalization Getting rid of data anomalies Session 5 Checkpoint Checkpoint y We know that ◦ Data redundancy is bad ◦ Designing an effective database requires proper methodologies and tools 5-2 proper methodologies and tools y You have a basic idea of the relational model y You are at least familiar with ER modelling So what’s next? So what’s next? y You have understood the business rules and captured them in the ER diagram ◦ In practice, this is an iterative process ◦ Refine with customers, programmers, etc 5-3 y Converting from ER diagram to tables ◦ involves a process called normalization ◦ Simply another database design tool 8/3/2009 2 What is normalization? What is normalization? y A process to evaluate and correct table structures ◦ Goal is to eliminate data redundancies ◦ why? 5-4 y Process is mechanical ◦ Goes through a number of stages ◦ Each stage is a “normal form” Example Example y BNG manages building projects ◦ Charges clients by billing hours spent on each contract ◦ Hourly rate is dependent on the employee’s 5-5 classification y Purpose of BNG’s data ◦ To generate a report about each project ◦ Also auxiliary data reporting Normalization Normalization y First stage is called the first normal form (1NF) y Generally, (n+1)NF is better than nNF y For most situations, 3NF is the furthest 5-6 For most situations, 3NF is the furthest we go y Higher normal forms have less redundancies ◦ Not always desirable ◦ why? 8/3/2009 3 Example Example (cont.) cont.) 5-7 Example Example (cont.) cont.) 5-8 What’s the problem? First normal form (1NF) First normal form (1NF) y A relation (or table) must not contain repeating groups ◦ A group of multiple entries can exist for any single key attribute occurrence 5-9 ◦ Goal of 1NF is to get rid of repeating groups y Informally ◦ A “key” should not identify a group of records or rows ◦ A “key” should identify one record 8/3/2009 4 A table not in 1NF A table not in 1NF...
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This note was uploaded on 09/27/2009 for the course SEB 323 - S taught by Professor Professor during the Three '09 term at Deakin.

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Week 5 (Wednesday and Friday) - 8/3/2009 1 Normalization...

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