Download Final - NCC Education

Database Design and Development
3 November 2015
Marking Scheme
This marking scheme has been prepared as a guide only to markers. This is not a set of
model answers, or the exclusive answers to the questions, and there will frequently be
alternative responses which will provide a valid answer. Markers are advised that, unless a
question specifies that an answer be provided in a particular form, then an answer that is
correct (factually or in practical terms) must be given the available marks.
If there is doubt as to the correctness of an answer, the relevant NCC Education materials
should be the first authority.
Throughout the marking, please credit any valid alternative point.
Where markers award half marks in any part of a question, they should ensure that
the total mark recorded for the question is rounded up to a whole mark.
Answer ALL questions
Marks
Question 1
a)
What is the chief concern of data conversion with regard to the implementation of
a new database system?
Data conversion – addresses the questions as to how data will be acquired
and possibly changed if the new database system is to replace an already
existing system (1 mark for acquired/changed). The source database could
be an already computerised system and some form of transfer software
might have to be used (1 mark). Alternative marks can be awarded for
mentioning data input from manual systems, writing SQL scripts that can
be used for transferring from flat files, or other relevant examples.
b) Define the term attribute and provide ONE (1) example of the term.
The qualities or property of an entity corresponding to a column in a table
(1 mark).
2
2
Award 1 mark for a valid example such as Customer_Name on a
Customers table (1 mark).
c)
State THREE (3) types of cardinality available in an entity relationship model and
provide ONE (1) example of each type.
6
The maximum number of marks awarded to this question is 6. Award 1
mark for indentifying a cardinality and award 1 mark for a relevant example.



One-to-one (example: a driving school where a lesson has one
customer)
One-to-many (example: a college where a course has many students
but each student has one course)
Many-to-many (example: a college where a module has many
students and each student can take many modules)
Total: 10 Marks
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Marks
Question 2
a)
Briefly explain what is meant by the concept of an insert anomaly and provide
ONE (1) example of the concept.
An insert anomaly is where a table is not properly normalised and errors
inserting data results. (1 mark)
3
Award up to 2 marks for a relevant example. For instance: a table that
records students, the activities they do and the prices of those activities. If
we want to record a new activity but no-one has yet taken it we cannot do
so because we need a StudentID because the StudentID is part of the
primary key and therefore cannot be null. This is an insert anomaly.
Note: Award 1 mark for a partially correct example.
b) Define the terms synonyms and homonyms and explain why they might be a
source of problems when trying to identify entities during database development.
You should provide ONE (1) example of a synonym and homonym to support
your answer.
7
Award 1 mark for each bullet point up to a maximum of 7marks:







Synonyms are two different words with the same meaning.
Homonyms are the same word that has a different meaning.
They are problems because they can cause confusion because
entities might not be identified properly
Examples of synonyms: Customer’, ‘Client’‘Student’, ‘Pupil’,
‘Scholar’.
Problem of synomyms: one entity might be misidentified as two
separate ones.
Examples of homonyms : Aisle and isle – one is a walkway one is an
island (note that homonyms don’t have to be spelt the same).
Problem of homonyms: two different entities might be misidentified
as the same one.
Total: 10 Marks
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Marks
Question 3
a)
Explain the ROLLBACK command in SQL and explain what it might be used for.
A command in SQL that returns a database to its previous state (1 mark)
Used to enforce integrity (1 mark) by undoing transactions that have put
the database in an inconsistent state (1 mark).
3
b) What issues with a large database system might cause a developer to consider
the use of a CASE tool?
In a large system with lots of entities there could potentially be many
relationships (1 mark). The task of cross-referring every entity to every
other entity would become too large to complete effectively (1 mark).
Alternative answers could emphasise other aspects of complexity such as
numbers of attributes, etc.
2
c)
5
What features are provided by CASE tools that aid the development of larger
database systems?
A CASE tool would have an entry where all the entities would be listed (1
mark) and a check could be made of all the relationships between them (1
mark).
Other uses and functions of CASE tools could also be credited. Award 1
mark for each bullet point up to a maximum of 3 marks:







Automation of routine functions
Storage of metadata
Project management
Support for methodology
Effective change management
Visual interface for users
Overview of different aspects of the project.
Total: 10 Marks
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Marks
Question 4
Explain the concept of redundancy in database design and provide ONE (1)
example of the concept.
Something is redundant if it is not needed (1 mark). It may be the case that,
during the process of design, structures (entities, attributes, relationships)
(1 mark) may have been created that are not really necessary (1 mark). An
example, is a DVD rental business where there are three entities, Customer,
Rental, Film. A ‘rented’ attribute on Customer is not needed because the
films rented is shown on the Rental entity (award 2 marks for this or
another example).
5
b) Why might a relationship that is time or context dependent be problematic in a
database system? You should provide ONE (1) example to support your answer.
If there is a relationship that exists and that has a time element, it is
important to make sure it is not lost when a situation changes (1 mark). For
example, if someone had qualifications that were based on where they
worked, we need to ask what happens to those qualifications if they move
job. Do they go with the person? If so, how do we model it? (Up to 2 marks
for this or another example)
3
Define the term candidate key.
A candidate key should be a super key (or should uniquely identify a row)
(1 mark). However, ALL the attributes of this super key must be necessary
to uniquely identify it i.e. there should be no superfluous attributes that are
part of the key (1 mark).
2
a)
c)
Total 10 Marks
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Marks
Question 5
a)
Explain what is meant by a linear and an iterative approach to systems
development.
Award 1 mark for each valid point to a maximum of 5 marks. Candidates
must discuss both linear and iterative approaches for full marks –
maximum of 3 marks for discussing each approach. Sample response:
5
A linear approach is one such as the waterfall approach (1 mark). It
assumes a series of steps one after the other (1 mark). Iterative approaches
involve stages that can be revisited. (1 mark). This has the advantage of
being able to get things right in small steps rather than needing to get them
right all at once (1 mark). An iterative approach might involve innovative
techniques such as prototyping (1 mark).
b) Discuss the role that end users have in an iterative approach to database
development.
The users are involved at many stages in database development. (1 mark)
The users need to be involved in looking at the model so far in making
comments, suggesting changes as part of the prototyping process (up to 2
marks). The involvement of users throughout the life cycle is one of the
ways of making sure that requirements are met (1 mark), because users are
verifying them throughout (1 mark).
5
Total: 10 Marks
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Marks
Question 6
a)
Discuss the key issues that are the concern of database performance.
Performance refers to the amount of time transactions take (1 mark). As
well as queries this can refer to transactions containing other operations
such as updates, inserts and deletes. (1 mark) Query response is the most
common focus of performance and one which exemplifies the most
important issues (1 mark). But other operations can also be considered (1
mark). Queries and updates (including insertions and deletions) can be
affected in different ways. Often an index that improves performance of a
query can actually be slow to update. (1 mark) Transactions will normally
be measured against some benchmark agreed on with the users (1 mark)
6
b) What are the possible effects on performance of having derived columns in a
database?
Wherever the calculation is done, whether in the insert statement or
attached to the table definition or in a database trigger (1 mark), it will still
need to be performed when the relevant operation is carried out on the
database. (2 marks.)There is also the possibility that data can become
inconsistent. (1 mark)
4
Total: 10 Marks
Marks
Question 7
a)
Briefly explain the conceptual design stage of database development.
In conceptual design we look at data independently without being
influenced by models such as the relational model we will use to implement
(1 mark). At this stage, the design still leaves open the question of how the
requirements will be implemented (1 mark). We might consider a number of
different ways of implementing the requirements of the project (1 mark).
3
b) What are the main concerns of logical database design?
In logical database design, the model is constructed without regard for the
particular DBMS that will be used (1 mark). However, the data model
(e.g. the relational model) is known (1 mark). It is concerned with
identifying logical data structures such as entities (1 mark).
3
c)
4
Discuss the main activities of physical design.
In physical design, the database is designed with the target Database
Management System (DBMS) in mind. (1 mark) Therefore it entails
knowledge of the chosen DBMS, whether it is Oracle, MySQL, SQL Server
etc. (1 mark). Physical design entails designing the actual data structures
as they will be implemented using the DBMS. (1 mark) Metadata (data
dictionaries) for structures such as tables, columns etc. will be defined.(1
mark)
Total: 10 Marks
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Marks
Question 8
a)
Identify and briefly explain FOUR (4) options for propagation constraints between
linked tables in a database.
‘No action’ (1 mark) means the record in the table with the foreign key is left
as it is (1 mark).
8
‘Cascade’ (1 mark) means that any change (including a delete) is replicated
in the table with the foreign key in it (1 mark).
‘Set Default’ (1 mark) means that the change in the parent table causes the
record in the child table to be set to some sort of default (1 mark).
‘Set Null’ (1 mark) is similar to Set Default except that the table with the
foreign key has that foreign key set to Null (1 mark).
b) What is a sequence in a database system and what is it used for?
A sequence is a structure that generates a number one after the other (1
mark). It is used to populate fields such serial numbers or unique
identifiers such as primary keys (1 mark).
2
Total: 10 Marks
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Marks
Question 9
a)
Explain the role of a DBMS (database management system) in a distributed
database system. Your answer should refer to the concepts of concurrency
control and query optimiser.
Any DBMS that needs to operate for a distributed database will be more
complex than for a stand-alone database (1 mark).
More complex system catalogue: To keep track of potentially different
structures in different sites and to record location of specific structures (1
mark).
Concurrency control: Needs to be more sophisticated, for example, to
make sure an update that affects more than one site operates in such a way
to keep the database consistent and maintain integrity (1 mark).
Query optimiser: Tracing paths through tables for queries becomes more
complex when the tables may be fragmented across different sites (1
mark).
Finally, the DBMS itself must be distributed which means that tuning and
managing it becomes a more complex set of tasks (1 mark).
5
Alternative answers should be credited.
b) What is the concept of transparency and why is it important in distributed
databases?
Transparency refers to the concept that from a user’s point of view a
distrusted database should look like a single database (1 mark).
Transparency enforces the foundation rule of distributed databases (1
mark). From this it follows that each site should have local autonomy (1
mark) and that there is no reliance on a central site (1 mark). This is the
case whether the database is replicated or fragmented. (1 mark)
5
Total: 10 Marks
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Marks
Question 10
a)
Discuss the FOUR (4) key features of an OLAP (online analytical processing)
tool.
Consolidation: allowing aggregation of data. (1 mark)
Drilling down: this is the opposite of consolidation. It involves the breaking
down of data into finer levels of detail. (1 mark)
Pivoting: being able to analyse the same data from different viewpoints. (1
mark)
Multi-dimensional data: the way in which OLAP achieves the above is by
data structures that have been visualised as having lots of dimensions (1
mark).
4
b) How might a large chain of supermarkets use a data warehouse to identify trends
that could help their business be competitive?
Looking at what is sold against data about the customers (1 mark). Where
customers have loyalty cards, various pieces of information will have been
gathered about them (1 mark). For example, their age, sex, address and any
other information that may have been solicited and that they have been
willing to give (if they own a car, if they have children, if they own their own
house) (1 mark). Alternative sources of data should be credited.
6
Such data can be cross-referenced (1 mark) with their purchases so that
their buying habits might be noted and picture of the customer base
established that can used to market things like baby products, car
insurance etc. (1 mark) Even without volunteering data, information can be
gleaned: so if someone starts to buy nappies (diapers) then they will be
sent direct marketing information about other baby products (1 mark).
Note: Credit alternative valid examples.
Total: 10 Marks
End of Examination Paper
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Learning Outcomes matrix
Question
Learning Outcomes
assessed
1
2
3
4
5
6
7
8
9
10
3
2,4
4
2,3
3,4,5
4
3,4,5
4
1
1
Marker can differentiate
between varying levels of
achievement
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Grade descriptors
Learning Outcome
Understand the
enterprise application
of database systems
Understand how to
enhance the design of
and further develop a
database system
Be able to enhance a
logical database
design
Be able to develop a
physical database
design
Be able to enhance a
database system
using SQL
Pass
Demonstrate
adequate level of
understanding
Demonstrate
ability to perform
the task
Merit
Demonstrate robust
level of
understanding
Demonstrate ability
to perform the task
consistently well
Distinction
Demonstrate highly
comprehensive level
of understanding
Demonstrate ability to
perform the task to
the highest standard
Demonstrate
ability to perform
the task
Show adequate
development
Demonstrate ability
to perform the task
consistently well
Show sound and
appropriate
development
Demonstrate ability
to perform the task
consistently well
Demonstrate ability to
perform the task to
the highest standard
Show innovative and
highly appropriate
development
Demonstrate ability to
perform the task to
the highest standard
Demonstrate
ability to perform
the task
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Database Design and Development
© NCC Education Limited 2015