Tutorial on Database Schema - Slide 8 - Products at Amazon.com or Starbucks
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- Products at Amazon.com or Starbucks
- Product Types (Inheritance and Recursion).
Let's move on to the topic of Products. As you might imagine, this can be a complex area.
Two important aspects are Inheritance and Product Hierarchies.
- This diagram shows a 'Products' table that holds details that are common to all Products.
- It shows an 'Amazon_Books' table that holds details that are specific to Books from Amazon.
- It also shows a 'Starbucks_Products' table that holds details that are specific to Products from Starbucks.
- These two are Children of the Parent 'Products' Table.
- Therefore, this concept is referred to as Inheritance and is very powerful in the real world.
- On the diagram, it is shown by the circle with two short horizontal lines underneath it.
- Data Modellers define these as 'Sub-Types' of a 'Super-Type'.
- This diagram shows the Logical level of the Schema.
- At the physical level, this can be implemented in one of three ways :-
Recursive Product Hierarchy
- Three tables - exactly like the Logical level.
- Two tables - one for Amazon and one for Starbucks, with the common data items copied down from the Parent Table.
- One table - at the higher level, with common data items and those for Amazon and Starbucks all in one large table.
- The line that comes out of the Ref_Product_Types Table and then goes back in again is informally called a 'Rabbits Ear',
or more formally a 'Recursive Relationship'. It defines a Product Hierarchy.
- It means that any Product can be part of a higher grouping of Products, such as Categories, Types and so on.
- This is a very neat and powerful way to implement this concept.
- In our example, the 'parent_product_type_code' is a reference to the next highest level in the hierarchy.
- I introduce Suppliers at this point because Starbucks and Amazon.com are both Suppliers of Products within our Schema.
- This would be the starting-point for Schema involving a more detailed analysis of Suppliers.
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