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# OCR A2 Computing F453 Official Thread 22/06/2016 Exam Discussion watch

1. (Original post by Aydin7)
Attachment 550601
It's one of the scheduling algorithms(3.1.2)

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The scheduling algorithms are first come first served, round robin, system of priorities and length of job I thought?
2. (Original post by King_Kauko)
F453 June 2012 Q5(c)

Question:
https://gyazo.com/4be2438bdd00b410603bf86f88307bf9

Mark Scheme:
https://gyazo.com/35a616546b5b6120cfebcf5ef2770eab

Can somebody possibly explain this visually with a diagram? I understand how a queue data structure is used briefly and how its uses pointers but in context I'm a little confused. I got the first point but the rest confused me.

Thanks
This type of queue is a circular queue. It is different to an ordinary queue as circular queues are fixed size so they are easier to program than ordinary queues which are dynamic.

When adding the first item, the Next pointer is incremented, and so moves to the front of the queue (as this is a circular queue - think of it as a circle). The second item is then inserted, and Next incremented again one place to the right. However, you must check whether the queue is full before adding the next item. Circular queues are "full" if they have one empty space.

https://en.wikipedia.org/wiki/Circular_buffer

Sorry I am unable to upload a diagram at the moment.
3. (Original post by Dapperblook22)
This type of queue is a circular queue. It is different to an ordinary queue as circular queues are fixed size so they are easier to program than ordinary queues which are dynamic.

When adding the first item, the Next pointer is incremented, and so moves to the front of the queue (as this is a circular queue - think of it as a circle). The second item is then inserted, and Next incremented again one place to the right. However, you must check whether the queue is full before adding the next item. Circular queues are "full" if they have one empty space.

https://en.wikipedia.org/wiki/Circular_buffer

Sorry I am unable to upload a diagram at the moment.
Great explanation!
4. (Original post by ryanroks1)
Great explanation!
Fantastic! Good job I asked or wouldn't of realised they could question circular queue structures too
5. So our problem about the question on the F452 paper regarding fixed length and variable records, turns out not to be a problem. Here is what OCR have sent in response to the Tuesday exam, I think it's fare enough

..........

GCE computing F452 examinationThank you for your email regarding the GCE computing examined unit F452.You state that Question 1d is not covered by the specification content for F452 as the question asked about fixed-length and variable-length variables. Just to clarify the question refers to fixed and variable length records (and not variables as you suggest).The question was linked primarily to point 3.2.3 (d) in the specification, ‘design and implement a record format’. There were further loose links with 3.2.3c & 3.2.3f.In order to design a record format one of the primary questions one must ask is whether it is of a fixed or variable length. We recognise this is an aspect of record design that has not been asked in past papers and that getting full marks in this question represents a high level of challenge, however, this does not deem it an invalid question.
6. I've come across this a few times in past papers but it seems like OCR use machine code and object code interchangeably? Not sure if it is just me but does anyone know the main difference between the two terms?
7. (Original post by jamie.mair)
I've come across this a few times in past papers but it seems like OCR use machine code and object code interchangeably? Not sure if it is just me but does anyone know the main difference between the two terms?
Yes, these terms can be used interchangeably. The same applies with 'high level code' and 'source code' - you'd get marks for either
8. (Original post by ryanroks1)
Yes, these terms can be used interchangeably. The same applies with 'high level code' and 'source code' - you'd get marks for either
9. (Original post by Aydin7)
Same again - both would be accepted. We were taught jobs so it's what I tend to stick to, although the mark scheme favours users, particularly for round robin. I believe it does mention in the notes section and on the examiner's reports that both would gain credit, so just stick to whichever you're used to
10. (Original post by ryanroks1)
Same again - both would be accepted. We were taught jobs so it's what I tend to stick to, although the mark scheme favours users, particularly for round robin. I believe it does mention in the notes section and on the examiner's reports that both would gain credit, so just stick to whichever you're used to
Thanks!
11. Does anyone else feel that sometimes the mark scheme answer isn't really relevant to the actual question? So like when it asks you the purpose of something and the answer just describes what it is but the two aren't really the same.
12. How has everybody learnt object oriented, struggling!
13. I find it so infuriating when the same question comes up on two different papers but the mark scheme is completely different for each!!!!! How are we meant to know what they decide the uses of the accumulator are on that specific day?
14. FFS can anyone explain why these are the PURPOSE of lifelines apart from shows when active???
•  (Vertical) dotted lines
•  Top to bottom in time order/sequence of events
•  Lifelines are either infinite or finite
•  Shows when active/inactive
•  Rectangles on the lifelines show methods
15. (Original post by lordyP)
FFS can anyone explain why these are the PURPOSE of lifelines apart from shows when active???
•  (Vertical) dotted lines
•  Top to bottom in time order/sequence of events
•  Lifelines are either infinite or finite
•  Shows when active/inactive
•  Rectangles on the lifelines show methods
It's really frustrating - we're always taught to look out for the question hooks yet they can't even do it themselves! I'm just gonna try to mention everything I know on questions like that - only tactic I can think of really.
16. (Original post by geekface98)
So our problem about the question on the F452 paper regarding fixed length and variable records, turns out not to be a problem. Here is what OCR have sent in response to the Tuesday exam, I think it's fare enough

..........

GCE computing F452 examinationThank you for your email regarding the GCE computing examined unit F452.You state that Question 1d is not covered by the specification content for F452 as the question asked about fixed-length and variable-length variables. Just to clarify the question refers to fixed and variable length records (and not variables as you suggest).The question was linked primarily to point 3.2.3 (d) in the specification, ‘design and implement a record format’. There were further loose links with 3.2.3c & 3.2.3f.In order to design a record format one of the primary questions one must ask is whether it is of a fixed or variable length. We recognise this is an aspect of record design that has not been asked in past papers and that getting full marks in this question represents a high level of challenge, however, this does not deem it an invalid question.
17. (Original post by ryandaniels2015)
How has everybody learnt object oriented, struggling!
Any help/resources??
18. Can someone help me or send me the coding for task 2 and the design part would mean a lot if someone could help me I'm really stuck.

Some automated troubleshooting programs identify certain keywords in the customer’s query to provide potential solutions to the query.

For example, ‘There is no display on my mobile phone screen.’

The keywords ‘display’ and ‘phone’ would link to common problems with a phone display.

Analyse the requirements for this system and design, develop, test and evaluate a program to identify keywords in a query typed in by the user and provide a linked solution to common problems related to a mobile device from a selection stored in a text file or database. You will need to identify appropriate keywords that can be linked to general advice related problems. You need to account for variations in the form of the user input e.g. one user may query ‘There is no display on my mobile phone’, another user may query ‘My phone screen is blank.’

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19. (Original post by ryandaniels2015)
Any help/resources??
- Self contained object contains methods, attributes /data
- Program spit into objects, used by other objects to build a complex system
- Uses encapsulation, this is the combining of methods and attributes to ensure data integrity, the attributes can only be accessed through defined methods
- May use Inheritance.....etc
20. (Original post by MrSplash)
- Self contained object contains methods, attributes /data
- Program spit into objects, used by other objects to build a complex system
- Uses encapsulation, this is the combining of methods and attributes to ensure data integrity, the attributes can only be accessed through defined methods
- May use Inheritance.....etc
THANKS!

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