For each of the following enterprise constraints decide whether - it is already

Question

For each of the following enterprise constraints decide whether

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

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

- cannot be expressed in the EER model below 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

(b) 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

The enhanced entity–relationship (EER) model (or extended entity–relationship model) in computer science is a high-level or conceptual data model incorporating extensions to the original entity–relationship (ER) model, used in the design of databases.

It was developed to reflect more precisely the properties and constraints that are found in more complex databases, such as in engineering design and manufacturing (CAD/CAM), telecommunications, complex software systems and geographic information systems

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