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1. Entity-Relationship Models

Consider the following entity-relationship model which describes the relationship between a department store customer and charge accounts operated by the store.  Which statement is NOT true:

1. a customer is not a customer unless they have an order

2. an order is for exactly one customer

3. a customer does not necessarily have to have an order

4. an order cannot belong to two customers

5. a customer may have many orders.

2. Entities

An entity in an entity-relationship model is defined as:

1. an external agent which carries out a process or activity

2. something of interest, which starts or terminates a process

3. a measure which indicates the number of relationship instances in which an object can participate

4. something which happens at the boundary of the software system under consideration.

5. something of interest, about which data can be recorded

3. Entities and Instances

The following is a fragment of an entity-relationship which models part of a training company.  The training company offers courses.  Courses have presentations and  presentations are made by instructors.

The following shows some old instances of the data representing the entities COURSE, PRESENTATION and INSTRUCTOR.

In the options below, a piece of data has been identified whose relationships may or may not conform to the entity-relationship model given.  You should identify which piece of data does NOT have any errors. 

1. Instructor:  Spurr

2. Presentation:  17/4/97 in London

3. Instructor:  Wright

4. Presentation:  23/10/96 in New York

5. None of the above

4. Data Flow Diagrams

Consider the two sections of a data flow diagram shown below.  Which statement is most representative of the diagrams.

1. The diagrams are levelled and balanced.

2. The diagrams are not levelled and balanced because INSURANCE-RISK-FILE appears in both diagrams.

3. The diagrams are not levelled and balanced because SPECIAL-RISKS-FILE appears only in one diagram.

4. The diagrams are levelled and balanced because INSURANCE-RISK-FILE is a global file used in a number of places and it is therefore appropriate to show the file in both diagrams.

5. The diagrams are levelled and balanced because SPECIAL-RISK-FILE is a local file used only by process 2.2 and therefore appears only on one diagram.