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Embed code for: Presentation Higher DB Alternative Conceptions
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Common errors in understating that students have when working with relational databases
Higher Database Alternative Conceptions
What is it pupils find difficult and why?
What Mistakes Have You Seen?
Write down as many common mistakes that pupils make when working with databases and answering database questions as you can
Share these with your group
Alternative Conceptions Reminder
Not all mistakes are caused by alternative conceptions
The reason why they’ve chosen that answer can help you to determine if they hold an alternative conception or if it’s just a lack of knowledge
Consistent reasoning but based on assumptions that don’t match how things actually work
These alternative conceptions have been identified by pooling together the experience of many teachers who have taught databases for years.
This isn’t an exhaustive list as there are more PI questions we don’t have time to discuss. There is also a collection of PI questions for N4/5 level.
As far as we are aware there is no coherent body of research on alternative conceptions in relational databases.
Selection of PI questions
For each question what is the correct answer
Which wrong answer(s) are students most likely to choose?
Why would they choose that answer?
Q. When reading a relationship between 2 entities, the relationship is read:
from left to right
from right to left
from left to right and from right to left
A relationship is uni-directional from one entity to another in reading order
A hospital uses a relational database to store details of wards and patients in two separate entities. Each ward in the hospital looks after many patients while each patient can be resident in only one ward.
Q. Which ERD correctly models the hospital system?
A relationship is time independent instead of at a specific moment in time.
takes part in
Q. Look at the diagram below and choose the ERDish sentence that describes the relationship.
Each Student can take part in one or more Sports.
Each Sport can be performed by one or more Students.
Each Student takes part in one Sport, each Sport is performed by one or more Student.
Each Sport can be performed by one or more Students, each Student can take part in one or more Sports.
Here is part of a relational database showing the tracks on a CD.
Q. What type of relationship exists between this CD and the tracks?
Relationships between entities always match what can happen in real life
Alternative conception for B
A relationship is uni-directional from one entity to another
Alternative conception for D
Entities that are indirectly related can be joined directly together.
DriveAway Ltd are a car hire company with locations in six cities throughout the UK: Aberdeen;
Glasgow; York; Birmingham; London and Portsmouth.
Each location has a unique ID number. A wide range of cars are available at each location. Customers rent cars for a specific time period. The rental system operates under the following conditions.
One customer can make many rentals.
Each car is associated with one location.
Q. Which E-R Diagram represents the data model.
Q. Which term best describes this image?
Relational databases have the same structure as flat file databases- File, Record, Field
The table is the database because it has all the information
Q. Which of the following terms best describes this image
New records can be added to a table with a foreign key value that doesn’t have a corresponding entry in the linked table yet.
A relational database is used to store details of the ski trails available in various holiday resorts. A table called Resort is used to store details of 7 different ski resorts.
A table called Trail is used to store details of the 181 trails in those 7 resorts. Part of that table is shown on the right
Q. A new ski resort with 12 ski trails has been opened in Scotland. Details of the trails must be added to the database . How should data about the new resort and it’s trails be added to the database?
Data about the new ski resort must be added to the Resort table after data about the trails has been added to the Trail table.
Data about the new ski resort must be added to the Resort table before data about the trails can be added to the Trail table.
Data about the new ski resort and its trails can be added at any time as soon as the information is available.
Lookup value from MEMBER table
Lookup value from DVD table
Q. The screenshot shows part of a data dictionary. Which one of the following fully describes the loan table
The Loan table has three primary keys
The loan table has a compound key consisting of: Member Number, DVD Code and Date Hired
The DVD Code in the Loan table is a primary key
Look at the following data model.
Q. The company want data showing the number of rentals for each location. Which entities are required to produce this?
Location, Car, Rental
A relational database stores details of customers, products and orders in 4 separate entities:
The database is used to support an e-commerce website. An HTML form is used to capture details of all orders placed.
Q. Which of the following statements is true?
The database file contains 4 related tables and the HTML form.
The database file contains 4 related tables.
The database file contains 4 related tables, the HTML form and PHP script used to add new order details to the Order and OrderItem tables.
Alternative Conception: A relationship is uni-directional from one entity to another
Correct Answer C – all relationships need to be read in 2 directions – from left to right AND from right to left.
A – If a relationship makes sense reading from left to right it’s the correct one.
B – If a relationship makes sense reading from right to left it’s the correct one.
Alternative Conception: A relationship is time independent instead of at a specific moment in time.
Correct Answer D) This ERD states that each ward looks after many patients; it also states that each patient is looked after (or is resident) in only one ward.
This ERD states that each patients is looked after (or is resident) in many wards.
This ERD states that a ward looks after only one patient; it also states that each patient is looked after (or is resident) in many wards.
This ERD states that each ward only looks after one patient,
Correct Answer D – the diagram is read in 2 directions – from left to right AND from right to left.
A – this sentence only describes the relationship from left to right. All relationships can be read in 2 directions; from left to right AND from right to left.
B – this sentence only describes the relationship from right to left. All relationships can be read in 2 directions; from left to right AND from right to left.
C – although this sentence describes the relationship in 2 directions, the relationship in the diagram, indicates that each Student can take part in one or more sports.
Alternative Conception: You can work out a relationship using your own knowledge instead of the information provided.
Correct Answer B) One CD has many tracks
Learner is just guessing as a CD would never just have one track.
One CD has many tracks but one track isn’t on many CDs in this example.
One CD has many tracks and one track can be on many CDs. This happens all the time with best of collections etc.
Correct Answer A: Many cars only have one location and a particular rental can only be for one car. Finally a customer can make many rentals but a rental is only for a specific customer.
B: Each car has one location so the pupil is thinking about specific instances not the collection of all cars.
C: Each customer can visit many locations because the pupil is using their intuitive knowledge rather than the description.
D: Each customer can rent many cars but this would be a many to many relationship however we need an intermediate entity to create the association.
Misconception:- The complete set of data in a table is the same thing as the database or the database file.
Correct Answer B) This is a table within the database and there can be more than one table
A) This is a database because it has all of the information that is being stored
C) Records are organised into a file so it’s a file.
Misconception- Data dictionaries are the same as a database, entity or table.
Correct Answer- D this is a data dictionary because it lists the data types and validation rules.
A- It lists the name of the entity and the attributes it has. Confusion between logical design and the design for the implementation.
B- This is all of the information stored in the database.
C- The information is arranged into a table.
Misconception: New instances can be added to a table with a foreign key value that doesn’t have a corresponding entry in the linked table yet.
Correct Answer B) Resort is a foreign key in the Trail table. By adding details of the new resort to the Resort table first, the resort name can then be selected from the drop down list of known resorts in the Trail table.
The trails need to be added before they are linked to a particular resort.
C) It doesn’t matter the order in which resorts and trails are added to the database.
Misconception: You can have more than one primary key in a table
Correct Answer B) A compound key is shown by a PK against each of the fields that will be included in the key.
A) These three fields are marked as PK so they are the primary keys
C) DVD’s are the things being loaned so DVD code is the main primary key
Correct Answer A:- Information from linking table Car is needed in order to match a particular rental to it’s location
B:- They haven’t read the question carefully enough
C:- They haven’t read the question carefully enough
D:- You need information about the locations and information about rentals
Misconception: User interface elements are part of the database data.
Correct Answer B) The database file stores the data in tables and all of the files to display the data are stored separately.
A) The database store the 4 tables and the HTML form as it’s being used to display the data. The learner doesn’t realise data return by the database engine can be processed by another program or system.
D) The database stores the data in the tables, the HTML form and the PHP script used to add new order details to the Order and OrderItem tables. The learner doesn’t realise other programs and systems can send queries to manipulate data stored in the database.ports.
D) The database stores the data in the tables, the HTML form and the P