In each case explain your answer briefly but clearly. Also decide whether questi

Question

In each case explain your answer briefly but clearly.

Also decide whether question 1 and question 2:

-is already expressed in the Enhanced Entity-Relationship model (EER) below

- is not already expressed in the EER model model below but could be expressed using only features of an EER model.

-cannot be expressed in the EER model using only features of an EER model.

Question 1) A table order originates from exactly one table of one restaurant.

Question 2) Two table orders dispatched at (roughly) the same time must originate from different tables.

Receives_by_phone Restaurant hone_line phone num Contains dateTi me billingNo total Order Originates from Table optional.orh number PhoneOrder TableOrder street wai ter deliveryAddress postcode city

Explanation / Answer

For Question 1:

Here Table is an week entity set whose strong entity set is Restaurant

Thus, primary key of Table is (name, number) i.e. name of the restaurant and table number of that restaurant

Now there is a many-to-one relationship from TableOrder to Table.

Therefore, for each entity in TableOrder (identified by billingNo) there is exactly one entity in Table (identified by name, number which is one table of one restaurant)

Thus, we can deside that Question 1 is already expressed in the Enhanced Entity-Relationship model (EER) below.

For Question 2:

Given EER allows more than 1 entity in TableOrder with different billingNo (primary key) but same dateTime to refer to a single entity in Table.

Thus, Question 2 is not already expressed in the EER model model below but could be expressed using only features of an EER model.

One possible solution is to make the relation Originates_form a ternary relation with Order_date entity having single attribute dateTime which maintains one-to-one relationship with Table. Also remove the dateTime attribute from Order. The one-to-one relation between Table and Order_date guarantees that only one order can be taken at a particular time for a particular Table.

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