Identify 7 mistakes by giving a number (e.g., 1, 2). Clearly explain each mistake and what should be the correct answer. An example is given below by naming the first mistake as number 1 (pointed by the arrow).
A rail transport company wishes to hold details of train services, stations and operators. Details include the following:
Trains: A train has a unique id code, a collection of days it runs on (Monday, Sunday etc.), and the
number of carriages it has. Each train must have at least one driver but can have many drivers that can drive it, and a driver may drive many trains. Each driver is identified by an employee number and a name. A train is designated as either an InterCity or District train though other types of train are possible. Each train must have an operator and not more than one operator. Each operator has a name and a phone number. The operator can operate many trains (or none at all!)
Stations: A station has a name and the number of platforms it has. All stations are classified as either
Main or District only. There are no other types of stations.
Timetable: A train has a number of stops at a station during its journey. It never visits the same
station twice on the same journey. At each stop, the arrival and departure times are recorded. A station
has many trains passing through it, often arriving at the same time, and a train visits many stations.
A new
at least 10 mistakes. Examples of mistakes include incorrect cardinality and participation in relations, missing or incorrectattributes, and incorrect constraints (e.g., disjoint, partial).
Identify 7 mistakes by giving a number (e.g., 1, 2). Clearly explain each mistake and what should be the correct answer. An example is given below by naming the first mistake as number 1 (pointed by the arrow).
Example: (1) Optional participation is incorrect: all trains must have at least one driver – so, minimum cardinality or participation must be mandatory ‘1
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