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Database Fundamentals

Database Fundamentals. Why use a database?. Putting all data into a single file simply doesn’t work because- Redundancy Insertion/deletion/update problems when all data is in a single file Data integrity (data can’t be trusted) . Why must a database be “normalized?” .

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Database Fundamentals

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  1. Database Fundamentals

  2. Why use a database? Putting all data into a single file simply doesn’t work because- • Redundancy • Insertion/deletion/update problems when all data is in a single file • Data integrity (data can’t be trusted)

  3. Why must a database be “normalized?” Normalization is just a fancy word for “putting the data into tables that make sense and will not cause errors.”

  4. What is a “data model” A data model is like an architectural blueprint for a database. It shows- • Table relationships • The numerical relationships between tables (called “cardinality”) • Table relationship rules (referential Integrity, cascading updates/deletes, etc.)

  5. Why Cardinality? Cardinality is the numerical relationship between tables. It is need to show how the occurrence of one record in a table relates to other tables.

  6. An Example of a 1 to Many relationship For example, a customer order may have many orders but a particular order can only refer to 1 customer. An order can only be associated with one customer but a particular customer can have many orders. This is shown as 1:M

  7. Crow’s Feet Notation 1:M A particular customer may have 0 or many orders in the orders table. A particular order can only be related to a one and only one customer.

  8. Microsoft Access 1 to Many

  9. Good News Most cardinalities (the numerical relationship between tables) in a database are- 1:M (one to many)

  10. Any more Cardinalities? The one to one cardinality (1:1) is rarely needed but it is sometimes used for the following reasons- • Security of specific data • Performance (speed of database access) • When only a few records will ever contain a value for a particular field (ex. Employees with stock options)

  11. How important is a data model? Very A poorly constructed data model will likely result in bad data and unintended actions occurring in the database.

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