Continuation of ER diagrams(entity relationship diagram)
- Cardinality Constraints
[1...1] A person likes only one country
[2...3] Each country is liked by 2 or 3 person
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In general for [i...j] 0 <= i <= j such that i and j belong to Integers
2 or 3 person can buy 1 or 2 products from 3 or 4 vendors
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Example
Buys{Robert, Apple, Monitor}
Buys{Robert, IBM, Computer}
At this point Person and Product constraints are matched
Buys{Joe, Apple, Computer}
Buys{Bob, Apple, Keyboard}
Buys{Joe, IBM, Mouse}
Buys{Bob, IBM, Headphone}
And at this point even the Vendor constraints are also matched
Buys{Robert, Apple, Computer}
At this point we can see that Person and Vendor are with in their constraints, whereas Product is out of its constraints because we have used Computer more than 2 times