Read the following definitions relating to data modelling. One describes the conceptual data model, another the logical data model and another the physical data model. Which one is the physical data model?
This model takes into account the architecture model (whether the target database is relational, object-oriented, etc). Arriving at such a model involves mapping the conceptual model to one suitable for implementation using a particular type of DBMS.
The target data model is refined to a more detailed level and takes into account both the facilities and constraints of the target DBMS (such as Oracle).
Arriving at such a model involves identifying the entities, attributes, relationships and constraints in an application. It is high-level model which is not concerned with implementation considerations (such as whether or not a relational DBMS is to be used) or physical considerations (such as concerns about physical storage requirements)
An entity is identical to a table in a relational database. True or false?
True
False
Listed below is data relating to students. Which one of the following is likely to be an entity and not an attribute?
Date of birth
Course
Student number
Grade
In a Student Library application a student is allowed one library card. What is the cardinality of the relationship between an entity Student and an entity Library Card?
One-to-one
One-to-many
Many -to-many
In an application which keeps information on employees and the projects to which they are assigned, we could describe the relationship between an entity Employee and an entity Project thus: ______ employee is assigned to zero or more projects; ______ project has one employee assigned to it. The missing word (in both cases) is:
One
One or more
Zero
In an application which keeps information on cinemas and the films shown at the cinemas, we could describe the relationship between an entity Film and an entity Cinema thus:
One film is shown at zero or ______ cinemas; One cinema is showing one or ______ films.
The missing word (in both cases) is:
One
More
Zero
Read the following:
a) For a mandatory relationship every occurrence of an entity participates in the relationship; b) For an optional relationship it is not possible that an occurrence of an entity can exist independently c) The membership class of a relationship defines whether it is mandatory or optional for an entity to participate in a relationship.
One of the sentences above is incorrect. Which one?
A
B
C
Read the following definitions relating to keys for an entity:
a) A key that consists of more than one attribute of the entity. b) A unique identifier for the entity which is chosen from the possibilities of all the unique identifies for the entity. c) A key which is an attribute (or set of attributes) which is a unique and irreducible identifier for the entity. There may be several of these for an entity.
Which of the sentences above is the definition for a candidate key?
A
B
C
The main phases involved in producing the conceptual data model are given here but in the wrong order. Which phase should appear second last in the list?
Define the relationships
Refine the model as necessary
Complete each entity with all its attributes
Define the entities
Identify the initial structure of the model
Establish the key attributes for each entity
Validate the model by checking that the model can support the processing requirements.
Read the following sentences relating to decomposing many-to-many relationships, one of the sentences is incorrect. Which one?
When converting an entity-relationship model to the relational model a many-to-many relationship is decomposed to produce three relations.
After decomposition, two relations represent each of the original entities and a new relation, the link relation, is introduced.
The link relation contains a composite primary key made up of the primary keys of the original entities.
After decomposition we end up with two one-to-one relationships.