This slide show focuses on the seven most common mistakes software developers make while designing databases and how to correct them. The good news is that following some simple data modeling fundamentals can lead to a high-functioning database. Solomon Waters of Embarcadero Technologies demos these important fundamentals using ER/Studio. You will learn: •The basics of normalization and data modeling •How to define consistent data definitions •Best practices for designing quality database applications

1. Seven Deadly Sins
Seven Deadly Sins
of Database Design
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Speaker: Solomon Waters
Embarcadero Technologies
b d h l i
San Francisco SQL Server User Group
San Francisco SQL Server User Group
June 2010
Mark Ginnebaugh, User Group Leader
mark@designmind.com
mark@designmind com

2. Seven Deadly Sins of
Database Design
Solomon Waters
Manager, Software Consulting
Embarcadero Technologies
solomon.waters@embarcadero.com
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3. Common Mistakes
Seven Deadly Sins of
Designing Databases
Solomon Waters
Manager, Software Consulting
Embarcadero Technologies
solomon.waters@embarcadero.com
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4. Agenda
• Topic
– Seven Deadly Sins Common Mistakes of Designing Databases
• What we’ll learn
– Pitfalls of a poor database design
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– Basics of normalization
– How to communicate a database design effectively
– How to avoid some of the most common mistakes made when designing databases
• Q&A
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5. 7 Deadly Sins Common Mistakes
1. Poor or no documentation for database(s) in production
2.
2 Little or no normalization
3. Not treating the data model like a living, breathing
organism
4. Improper storage of reference data
5. Not using foreign keys, check constraints, and/or
defaults in the database
6. Not using domains and naming standards
7. Not choosing and/or indexing keys properly
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6. 7 Deadly Sins Common Mistakes
1. Poor or no documentation for database(s) in production
• Problems
– No central documentation of database structure(s)
– Inaccurate documentation of database structure(s)
( )
– No documentation at all of database structure(s)
• Ramifications
– Developers, DBAs, architects, etc. are not on the same page
– Inability to respond to change
– No communication between developers, DBAs and architects
• Solution
– Start from the bottom-up, i.e. reverse engineer database(s) to build
documentation
– Validate models prior to publishing them
– Use HTML reporting and Portal to communicate to users
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7. 7 Deadly Sins Common Mistakes
2. Little or no normalization
• Problems
– Database denormalized unnecessarily (i.e. too much)
– One large table has been built to store “everything”
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– Multiple values in one column or repeating values in a table
• Ramifications
– Performance may be better, but maintenance can become a nightmare and
expensive
– Lots of NULLs if specific columns don’t have values for specific rows
– Unneeded application code needed to parse out specific values
• Solution
– Understand the basics of database normalization
– Know when and how to normalize when needed
– Industry models can help as a reference or templates
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8. 7 Deadly Sins Common Mistakes
2. Little or no normalization (cont’d)
• First Normal Form:
– Eliminate duplicative columns and repeating values in columns
• Second Normal Form:
– Remove redundant data that apply to multiple columns
• Third Normal Form:
– Each column of a table should be dependent on the primary key
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9. 7 Deadly Sins Common Mistakes
Len Silverston UDM
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10. 7 Deadly Sins Common Mistakes
3. Not treating the data model like a living, breathing
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organism
• Problems
– Modeling is done upfront then never updated once the database changes
– Design is not completed/reviewed for flaws before moving to production
– Changes made in production/database without updating data model
• Ramifications
– Implementing changes becomes problematic and expensive
– Undocumented data can lead to security and regulatory issues
– Design missing functionality that the business needs
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• Solution
– Plan out the design of the database conceptually, logically and physically
– Review the design with both technical AND non-technical stake holders
non technical
– Update the models as changes occur or better yet, update the model first!
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11. 7 Deadly Sins Common Mistakes
3. Not treating the data model like a living, breathing organism
(cont’d)
• Uncontrolled Changes
– Models become out-of-date and no one uses
them
– Reports from out-of-date models are useless
– No understanding what has changed
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12. 7 Deadly Sins Common Mistakes
3. Not treating the data model like a living, breathing
organism (cont’d)
• Controlled Change
– Define a means of communicating
changes
– Don't let models get out of date
– Build a process to update models
– Automate the process
– Ultimately drive changes from the
model
– Define a means of archiving/tracking
changes
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13. 7 Deadly Sins Common Mistakes
4. Improper storage of reference data
• Problems
– Reference data (codes, lists, valid values) stored in more than one place
– Reference data stored in application, not in the database
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– Constraints not placed in the database
• Ramifications
– More work is needed when code values change
– Database can’t enforce consistency and accuracy of values
– Problems when data is sourced from another place
• Solution
– Leverage data models to store data values
– Keep them up to date with the database
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14. 7 Deadly Sins Common Mistakes
5. Not using foreign keys, check constraints, and/or
defaults in the database
• Problems
– Legacy system with check constraints and foreign keys enforce by application
– Inconsistent data because lack of constraints
– Using NULLs instead of defaults
• Ramifications
– Incredibly difficult to document system for other users
– Special code becomes the norm, not the exception
– Poor data quality can result if standards are not followed
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• Solution
– If it can be enforced in the DDL at creation time do it
– Use tools to infer relationships
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15. 7 Deadly Sins Common Mistakes
6. Not using domains and naming standards
• Problems
– The “same” columns defined with different data types in different tables
– The “same” column named differently in different tables
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– Cryptic or non-descriptive names that don’t identify the use of a column
• Ramifications
– Inconsistent and/or poor data quality
– Confusion and wasted time for future developers, DBAs, architects, etc
– Inaccurate use of column
• Solution
– Define a common list of domains users can leverage
– Have a common naming standard dictionary to abbreviate logical to/from
physical names
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16. 7 Deadly Sins Common Mistakes
7. Not choosing and/or indexing keys properly
• Problems
– Using surrogate keys that don’t uniquely identify the data
– Poorly choosing a p
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y y (too many columns, column is updated frequently)
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– Not indexing foreign keys
• Ramifications
– Each row is unique but not the data which leads to redundant data
– Updating or changing primary keys is not trivial
– Performance issues when updating data or accessing related data often
• Solution
– Use a combination of natural and surrogate keys where applicable
– Follow the SUM rules when choosing PKs: 1. Static 2. Unique 3. Minimal
Columns
– Use model validation wizard to enforce rules
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17. About the Speaker
• Solomon Waters
– Manager, Software Consulting
– solomon.waters@embarcadero.com
• Resources
– COMPANY: http://www.embarcadero.com
– BLOG: http://datamodel.wordpress.com
– PRODUCT INFO: http://www.embarcadero.com/products/er-studio
– DOWNLOAD: https://downloads.embarcadero.com/free/er_studio
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18. Thank you!
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19. To learn more or inquire about speaking opportunities, please contact:
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Mark Ginnebaugh, User Group Leader
mark@designmind.com