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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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Presentation Transcript
why use a database
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
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.”

what is a data model
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.)
why cardinality
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.

an example of a 1 to many relationship
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

crow s feet notation 1 m
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.

good news
Good News

Most cardinalities (the numerical relationship between tables) in a database are-

1:M (one to many)

any more cardinalities
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)
how important is a data model
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.