For each of the following enterprise constraints decide whether • itisalreadyexp
ID: 3602132 • Letter: F
Question
For each of the following enterprise constraints decide whether
• itisalreadyexpressedintheEnhancedEntity-Relationship model (EER) of Table 2 on the next page
• it is not already expressed in the EER of Table 2 on the next page but could be expressed using only features of an EER model.
• cannot be expressed in the EER of Table 2 on the next page using only features of an EER model.
In each case explain your answer briefly but clearly.
(a) A table order originates from exactly one table of one restaurant. [4 marks]
(b) Two table orders dispatched at (roughly) the same time must originate from different tables. [4 marks]
Receives by_phone Restaurantname phone_line phone num ontains dateTime total Order Originates.froTable (optional.or) number PhoneOrder TableOrder street waiter deliveryAddress postcode city Table 2: Enhanced E/R diagram for Questions 2 to 4Explanation / Answer
For explaining this two concept are important-
1:M relationship- This means one instance of entity on the left can be associated with many instances of entity at the right.
Total Participation (Double line between entity 'TableOrder' and relationship 'originates from')-
This means every entity in 'TableOrder' participates in atleast one relationship in 'Originates from'.
a) It is already expressed in the Enhanced Entity Relationship Model.
Explanation-
Entity 'Table' and 'TableOrder' are connected via relation 'Originates_From' in 1:M cardinality. Every order belongs to only one table of a restaurant. Total participation shows there is no Tableorder that doesnot originates from a table.
b) It is already expressed in the Enhanced Entity Relationship Model.
Explanation-
Again Entity 'Table' and 'TableOrder' are connected via relation 'Originates_From' in 1:M cardinality, which means one table can place many orders. So it is quite possible that two order originates from the same table (time could be roughly same).
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