CS10610 Databases: Practical 4
2008-2009
Objectives:
 To set up relationships between tables.
 To understand referential integrity (definition on Blackboard; Practicals -> Ref Integrity).
(a) Use the numbered points of information (requirement specification) to draw an Entity-Relationship (ER) diagram for a system to hold information on Oscar awards. Your E-R diagram should show
ENTITIES, RELATIONSHIPS AND PK FIELDS ONLY in addition to the justification for each side of
each relationship by adding comments to the diagram. The diagram has been started using the points
below
1. A film has many roles.
2. Each role is cast in 1 film
3. Each role is nominated for many awards
4: Each award has many roles nominated to receive it. The year of nomination is recorded and
Point 1
whether or not it was successful.
Has
Film
filmId {PK}
..1
Role
..*
Cast In
Point 4
Point 4
Point 2
..*
Nominated
to
Year,
Successful?
Award
shortCat {PK}
..*
Nominated for
Point 3
Study the above example. Copy down the E-R diagram and using the information below, add to it. The
slides from the lectures are available on the web page to help you if needed.
5.
6.
7.
8.
An Actor accepts many roles.
The actor’s name is recorded and their union number (unique).
Each role is given to only 1 actor
For each role, the role name is recorded.
Will role name be unique? If not, it should NOT be added to your E-R diagram.
A film may be nominated for more than one award.
For each film, the film ID (unique), title and director is recorded.
The year of nomination and whether or not it was successful is recorded.
An award has many films nominated to receive it.
The category of each award is recorded, and the short category (unique).
Convert your E-R diagram into a list of tables following the rules given in the lecture slides, starting with the
entities involved in any one-to-many relationships. Use the convention below:
TableName {primaryKey, field1, field2, foreign key*}
Remember that not all tables will have a foreign key (the linking field). Make sure that the primary keys and
foreign keys are indicated in your list of tables as shown above.
SIGN OFF POINT (1 of 3): E-R diagram
Get this work signed off.
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CS10610 Databases: Practical 4
2008-2009
(b) Go to the CS106 page on Blackboard and copy the database oscars_prac4.accdb from the
Practicals folder to the d:\docs directory. Open the database oscars_prac4 on the d drive in
Access.
Read through Tables  Guide to table relationships. Read the introduction and the sections
on Types of table relationships.
Have a look at the relationships window of the oscars_prac4 database (Database Tools tab).
Use the lecture notes on the web to help answer the following questions:
Are the foreign keys shown in your E-R diagram?
............................................................................................................................................
Where do the foreign keys first appear in the exercise?
............................................................................................................................................
Why do they appear only at this point?
............................................................................................................................................
............................................................................................................................................
Are the foreign keys shown in the relationships window?
............................................................................................................................................
IMPORTANT ASSESSMENT INFORMATION

Note that the Access relationships window is NOT an E-R diagram. The
relationships have already been implemented and it shows the foreign keys.
Drawing a diagram such as this in an exam would lose you a lot of marks.

E-R diagrams only show the primary keys. They are NOT the same as class
diagrams in Java.

A printout of the relationships window will NOT be acceptable as an E-R
diagram in the assignment. You should submit a true E-R diagram such as
those shown in the lecture notes or as illustrated in exercise a).
(c) Your objective now is to amend the design to record the cinema at which some of the films are
currently being shown. Use the following information to update your E-R diagram from a). Note
particularly the assumptions (not realistic but they keep the practical shorter!)



A cinema shows only 1 film.
A film can be showing at many cinemas.
For each cinema the cinema name and town are recorded. You may assume that the
cinema, town combination is unique.
Amend your list of tables to include the new information.
(d) Create a new table in the Oscars database to hold the cinema information. The Film ID field
(foreign key) should be of type number and Field Size long integer. (It must match the Film
ID field in the Films and Directors table; matching fields must be of the same data type, except
that a long integer number is allowed as a match for an Autonumber.) When you have designed
your table and set the primary key, save the design and close the table. You will not be able to
create a relationship while the table is open.
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CS10610 Databases: Practical 4
2008-2009
The FilmsAndDirectors table shows an acceptable use of an autonumber. All
films have some kind of identifying number. The film table merely uses the
autonumber facility as a tool for entering data. Using an Autonumber in your
cinema table would not be acceptable as there is already a unique field
combination (cinema and town)
(e) Read through Tables  Guide to table relationships  Create a table relationship. Now open
the Relationships Window if not visible. Add your new table to the window. Set up an
appropriate relationship between your new table and the Films and Directors table.
(f) Read through Tables  Guide to table relationships  Understanding referential integrity.
You should Enforce Referential Integrity now, before you enter any data. Don’t set the
Cascade Update … and Cascade Delete… checkboxes at this point.
(g) Add a few records to your new table. Use your imagination for cinemas if you wish, but the
Film ID should come from those in the Films and Directors table. Your records should
illustrate the fact that a film can be shown at many cinemas.
(h) Start a new query in design view, adding the cinema and the FilmsAndDirectors table. Notice
that the link that you set up in the relationships window between these two tables is
automatically added in the query window.
Design a new query that will show the filmID, title, director, cinema and town for a cinema of
the user's choice.
Inspect the results. The system uses the data contained in the foreign key - primary key (FilmId)
fields to look up the appropriate data from the FilmsAndDirectors table
SIGN OFF POINT (2 of 3): Parts (b)-(h)
You may continue to work on until a demonstrator becomes free.
(i) Close your database file and copy it onto the M drive. Then complete the final section
UNDERSTANDING REFERENTIAL INTEGRITY
(j) A database has integrity when you can trust the data within it. The following experiment is to
illustrate how referential integrity works and to show the reason for some common problems.
Work in pairs for this exercise but you should both note down the answers to the
questions.

Start a new blank database.

Create two tables,
Branch {branchCode, branchName}
Staff { staffNo, surname, branchCode* }
(branchCode is a single character text field)

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CS10610 Databases: Practical 4
2008-2009

Try to set up a relationship between the two tables using branchCode, enforcing
referential integrity.
What happens?
.........................................................................................................

Why?
...........................................................................................................

Set branchCode as a primary key on Branch and close the table. Now set up a
relationship between Branch and Staff, using the branchCode field, enforcing
referential integrity

Open both tables. Add these records to the branch table:
branchCode, branchName.
A
Aber
B
Bangor
C
Cardiff
D
Swansea

Now try to allocate a member of staff to a non-existent branch by adding the
following record to the Staff table
staffNo
surname branchCode
1
Bloggs
E

What happens
...........................................................................................................

why?
...........................................................................................................

Add the following valid records to the Staff table.
staffNo
surname
branchCode
1
Bloggs
A
2
Evans
B
3
Jones
A
4
Smith
C

Can you delete Smith’s record? ........................................................

Why? ................................................................................................

Can you delete the Bangor record from the branch table? ...............
Why? .................................................................................................

Can you delete the Swansea record from the Branch table? ............
Is it referred to by records in the staff table? ...................................
SIGN OFF POINT (3 of 3): Referential integrity exercise
Once the work is signed off, close your database file and copy it onto the M drive.
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