Database instance
I read a statement from an exercise: construct a database instance which conforms to diagram 1 but not to diagram 2. The diagrams are different n-ary relationships that have different relationships. Diagram 1 has a many to one to many to one relationship. Diagram 2 has many to many to many to one relationship. So, to really understand this problem, what does a database instance mean? Is it to make an example or abstract entities like a1, a2, or a3. Thanks for your time.
EDIT: Here is the exercise: Consider the E/R diagrams in figure (2).
a: Construct a database instance which conforms to diagram 2 but not to diagram 1
b: Construct a database instance which conforms to diagram 3 but not to diagram 2
The instances may assume values like a1, a2, a3 for the entity A, b1, b2, b3 for the entity B, and so on. (If you are unable to come up with an instance explain why.).
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Diagram 2 | C |
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| A |------------- -------------| B |
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Diagram 1
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| A |------------- -------------| B |
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Diagram 3
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| A |------------- -------------| B |
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In this context, it probably means just "build the database", so you just need to build the database structure (tables, foreign keys, etc.).
UPDATE: yes, I think I will stick with my opinion. You have to create a database structure that will fit this diagram (diagram describes the relationships of a table within a database) and entities are tables. Database instance only means database. A quick google search gives the answer:
"An organization with an employee database can have three different instances: production (used to store real-time data), pre-provisioning (used to test new functionality before release to production), and development (used by database developers to create new functionality). http://databases.about.com/od/administration/g/instance.htm
Good luck :)
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