Name:

Databases Answers

The OCR Specification says that you should be able to:

The Database Concept

describe a database as a persistent organised store of data explain the use of data handling software to create, maintain and

interrogate a database

The DBMS

describe how a DBMS allows the separation of data from applications and why this is desirable

describe the principal features of a DBMS and how they can be used to create customised data handling applications

Relational Databases

understand the relationship between entities and tables understand the components of a relational database, such as tables,

forms, queries, reports and modules understand the use of logical operators in framing database queries explain the use of key fields to connect tables and avoid data

redundancy describe methods of validating data as it is input

Past Paper Exam questions

Jan 2011

1. A teacher uses a database to store the marks of pupils from all year 9 classes.

(a) PUPIL and CLASS are two entities used in this database.

Explain the term entity.

A real world object ... about which data is stored in a database Corresponds to tables in the database

[2]

(b) The data for the first four pupils in the PUPIL table is shown below.

(i) State the primary key for the PUPIL table and explain your answer.

Primary KeyPrimary Key: PupilNumber

[1] Explanation

o It is a unique identifiero Two pupils cannot have the same PupilNumber...o ... but they can have the same surname, firstname or ClassCode

[2] (ii) The database also contains a CLASS table. The primary key for the CLASS table is ClassCode.

Explain why ClassCode has also been included in the PUPIL table.

ClassCode is used here as a foreign key To link CLASS and PUPIL Using the ClassCode, all the class details can be retrieved from the Class

table ... otherwise the class details will have to be rewritten everytime/to avoid

data redundancy

Explanations must link the two entities. e.g. “To find out in which class a pupil is” or “to create lists of students by class” is too vague as it does not require the ClassCode in CLASS to be the same as in PUPIL.

[3]

June 2011

2 A grocery shop uses a database with a DBMS to keep records of its stock.

(a) Explain what is meant by a DBMS.

A Database Management System/Used to manage the database May use SQL/allows database to be queried Provides facilities for creating tables/inserting data/viewing data/reporting Allows data structure to be independent of the program Allows relationships to be created between tables/Maintains integrity Provides security features/levels of access

[3] (b) The database uses forms and reports.

Describe each of these and give one example of how it would be used in the shop’s database.

Form

Aninput screen Allowing chosen data items to be displayed and edited Uses texboxes/drop down lists/checkboxes etc… When edited, the changes are updated in the database

[2] Example

Suitable example from shop eg enter new products

[1] Report

An output of the data in a database A snapshot of the data at a given time/when printed Of specified fields/Laid out in a specified format Aggregates may be calculated and displayed

[2] Example

Suitable example from shop eg weekly sales

[1]

Here is some data from the supermarket’s database.

(c) The shop runs queries using logical operators to select data for different purposes.

(i) State the ProductID of the products in the above sample which fit the following criteria.

Supplier = Killey’s

Answer: 0003, 0006award 1 mark if both answers present and no others

[1] Price > £1.00 OR Supplier = Hill Farm

Answer: 0001, 0002, 0004, 0008Award 1 mark if 0001, 0002, 0004 are all in answerAward 1 mark if 0002 and 0008 are in answerAward 1 mark if 0002 is not repeated and there are no extra answers

[3]

(ii) Write the criteria which can be used to select all products which are not discontinued and where the QuantityLeft is lower than the ReorderLevel.

Discontinued = False AND Quantity Left < Reorder Level

[3]

Jan 2012

3 Mrs Smith runs a dog sitting service that looks after dogs whose owners are going away on holiday.

Mrs Smith uses a database with two tables:• The table DOG stores the following data about each dog: DogID, name,

sex, weight, date of arrival, date of departure.• The table JOB stores the daily jobs that she needs to do with each dog.

(a) The DOG table contains fields for the sex and weight of the dog.

(i) Describe a validation check that can be done on the sex field.

Existence checko Male / Female (or similar) allowedo And no other entry possible

[2] (ii) Describe a different validation check that can be done on the weight field.

Range checko Must be a (real) numbero Must be positive

[2] An extract of the JOB table is shown below:

(b) Explain why DogID has been included in this table.

It is used as foreign key (in this table)o ... the primary key of the DOG tableo to link the two tableso allows us to find the details of the Dog to which each job relates /

do not need to re-enter dog details for each job

Not simply “to identify dog… but if they refer to the JOB table, i.e. “to identify the dog that a job refers to” then this is the same as the 4th bullet

[3] (c) Mrs Smith uses a query to select jobs using the following criteria:

(Time = “Afternoon”) OR (Time = “Evening”)

List the JobNumbers of the jobs that will be selected from the extract shown.

36, 37, 39 (correct answer only)[1]

(d) Mrs Smith wants to use database management software to create a report of all the jobs that she needs to perform on any given day, using data from the DOG and JOB tables.

In the space below, design a layout for the report.

There is a date There is a title Jobs are grouped/sorted appropriately (eg by dog, time or job type) Each job includes the Dog Name Each job includes the Dog ID Each Job includes the Job type Each job includes details

[6]June 2012

4 A DBMS is used to create customised data handling applications.

(a) State what the initials DBMS stand for.

Database management system[1]

(b)* Describe the features of a DBMS that can be used to create customised data handling applications and explain why using a DBMS is desirable.The quality of written communication will be assessed in your answer to this question.

Features Provides a set of tools for accessing/maintaining the database, eg to

define/create tables, run queries or define reports The application is independent from the data base itself Provides data integrity control (eg integrity checks, validation checks) Controls access to data, including security and multiple user access

Why desirable These can be set up before hand by expert and used by end user Separating application and database means the database can be

accessed separately by other means eg a desktop application and web application accessing the same data / other suitable example

Data is protected from corruption eg by multiple access [6]

Jan 2013

5 A social networking site uses a database to store the details of the people who have joined the site.

(a) Describe what is meant by a database.

A persistent... ... and structured/organised store of data Allows data to be queried/interrogated.

[2] (b) When a person joins the website, they need to enter some personal data which is validated using rules. For example, the date of birth must be in the past.

State one rule that could be used when validating each of the following.

Email address

Must contain an @ sign Must contain a full stop (after the @ sign).

[1] Gender

Must be one of Male, Female, (Other).

[1]

Password

Must have a given minimum length Must contain a non-letter.

[1] (c) Each user can upload several pictures. Each picture has a date and a comment.

The personal data of users is stored in a table called USER. The data about the pictures is stored in a separate table called PICTURE.

Explain why the data about the pictures should be in a separate table, and how the tables can be linked.

Avoids data repetition/redundancy/inconsistency... ... with the personal details of the user ... a user can have more than one picture/one to many The primary key of the USER is stored in the PICTURE table Where it is a foreign key.

[4]