AQA COMP3 June 2012 Exam Thread

if anybody can tell me if i would get the marks on 5) 12) 13) 18) 22) 29) it will be much appreciated.

Your answer for 12 is much better than mine. I was going to write about the 10 workstations but I resisted because I didn't think it was obvious enough. Which is a pathetic reason for not including it. I said that it is not appropriate for there to be no administrators in a network used by students. Also about dedicated servers, but I did feel like I was repeating myself with the next question.

also for the relationship diagram was it one customer can have many orders? i had 1 one to one and 1 one to many i think

Should have been two "one to many" relationships.

For the p2p question, i wrote about p2p being less secure compared to server, wud this be correct.

This was posted from The Student Room's Android App on my HTC Desire

hopefully i will at least get the B if not A. need a B in this and it wasnt too bad. made loads of silly errors tho.
i'll put down what i remember for my answers. some of it is wrong made quite a few silly mistakes so can people tell me if i got them right or not would be appreciated. also feel free to expand on it

1) file management; I/O system ; processing management
2) Rope was duplicated twice; everybody says its n^2 i thought it would be O(n) and both explanations make sense. I said linear cos it was comparing the search word with each item in the list until it was either found or it had reached the end of the list. maybe more than one answer is possible for this question? idk
3) The greater the bandwidth the larger number of bits that can be transferred per second
4) got the exact relationship between the baud rate and bit rate wrong >.<
5)hashing can be used to speed up table look up when looking for item in list
6) a hash function H is applied to a hash key K which generates a hash value H(K) which is stored in the table. something like that
7) a collision occurs when two hash keys point to the same hash value. A collision can be resolved by rehashing the hash value with the similar hash key which regenerates a new hash value. Open hashing can be used which records with the same hash value can be stored in the "next free location" in the table. etc
8) Space complexity
9) a recursive routine is a routine that calls itself
10) Bluetooth: a wireless networking protocol used for exchanging data over short distances from fixed and mobile devices; An example when the man with the laptop uses his phone to send photos (exchange photos) with/to his laptop;
11) encryption: the process of converting message data into a form that is not understandable without the key to decrypt it.
12) why use server based rather than p2p: it said 10 workstations are to be connected and p2p LAN is only suitable when there are less than 10 users, security is not an issue and users can be their own administrators, and the organisation has minimal growth in the forseeable future but over tiime the range of student courses increase vastly. therefore server based neetwork is used when p2p is not suffice. server based all processing takes place dedicated servers (not sure if i said the last bit :L) etc
13) thin client is where all processing such as system security, running of application programs, administration and other functions take place on a central server, and all clients act as dumb terminals with no processing power or limited- and no memory storage space. The central server consists of: file server used to store the users files; application server for running programs and a domain control used to store webpages (last one couldnt remember so it was bs dk if ill get the mark) Thick client is the opposite where there are no dedicated servers and all client workstations have equal processing power and memory storage space. Thick clients have less delay time between operations since fewer bytes of files are transferred.
14) time latency is the time delay between the moment the signal is first transmitted/produced and when its first effect starts-when it is first read/recieved;
15) digital certificates, where sender A digitally signs the message data using a trusted third party digital signature provider. this is so reciever B can authenticate that the message recieved has not been tampered with and is genuine.
cant believe i mixed this up int he exam...where you had to say the steps....-.- but anyways The processes required before A's message is sent to B are as follows:
• The message is hashed to produce a message digest.
• The message digest is encrypted with A's private key; this becomes the signature.
• The signature is appended to the message.
• The message is encrypted using B's public key.
• The encrypted message is sent to B.

The processes required to ensure that the message received by B is genuinely from A are as follows:
• B decrypts the message with B's private key.
• B decrypts the signature with A's public key to retrieve the original message digest.
• The decrypted message is hashed again to reproduce the message digest.
• If the decrypted digest equals the reproduced digest, the message has not been tampered with.
16) it wasnt a tree since there were cycles. It can only be a tree if there are no cycles. (no multiple vertex pairs)
17) normalisation: no non key dependancies; no repeated groups of attributes in a relation (no redundant data)
18) the database stuff i didnt include any "override" procedures idk if u do some say yes some say no think ill lose two marks on for each if yes.
i am not good with databases someone tell me if ill get anny marks think its wrong :L i said a new attribute (NumberOfCopies) should be created (now its obbvious copyID should have been created -.-) in the bookID relation. This has to be part of the primary key in the Loan relation too. something like that :L
19) SQL INSERT INTO i just copy pasted the details they gave me with no changes just for example bookID.BookName = "name given in q") something like that. is it correct? :L
20) i messed up on mantissa stuff i think...-40, then the next two i cant remember but for the -12.5 do u have to convert 12.5 into -12.5 using two's complement? i said 12.5 = 1100.1 so -12.5 is 0011.1 (i think i did it wrong no?) and then from there i did the rest of the calculations. exponent negative bring it to the left etc
21) the adjacency matrix i just put 1 where it was linked and where it wasnt i put 0
22) The point of using a stack is that it is a LIFO structure which includes pointers so it can help the algorithm know when to stop looping (head pointer) to prevent stack overflow/empty errors. Also to provide different values for the parameter each time it runs through the algorithm etc
23) inheritance diagram was easy. computer printer linked with directed arrows towards devices. and then the three others that were part of computer were pointed towards computer etc
24) the moore machine one was easy. just copy the values in the table
25) yes, then No
26) underflow, overflow cancellation error (not sure about the order of what i put for underflow overflow)
27)gateway is used to connect two networks using different protocols to ensure communication and exchange of data have been successful
28) first blank: program second blank: output - copied that from the book dk if its right tho according to what people have been saying :L
29) significance i waffled loads didnt exactly know what it wanted i said thats its impossible to create a program that takes another program as its input and determine whether it would halt or get stuck in a loop. therefore a UTM cannot solve this problem. something like that.
30) got those regex's wrong completely . put ab*c for the first one after crossing out the correct answer ab+c. and the second i put something long like [a,b]?0?1* which is most
probs wrong -.-
31) backus Naur form
anything i missed out? help modifications from people and telling me if i got them right what i got wrong would be much appreciated. Hope this helps!

What was the answer of the last question??? The depth-first-search algorithm?? do you remember??

I didn't understand why 1 should be the last to be fully explored (except in terms of the pseudocode they gave).

What was the answer of the last question??? The depth-first-search algorithm?? do you remember??

i couldnt do the last trace sorry!

Sorry to be such a pain, but someone please put me out of my misery.

How many marks will I get for these questions...

1) Name three managements that the OS has to do?



2) Why use thin network over thick (That 4 marker)?
All processing happens in the central server. Although processing is happening in the central server, it has no limited power. Thin network provide services such as Web 2.0, Ajax, Software as a service. The only hardware, that would need to be purchased is a server.

3) Turing machine Question (Fill in the blanks)?
1st blank - Implement a Turing Machine write a program
2nd blank - Outputs executing this program

4) What is halting problem (1 mark)?
When there is no application that can halt another application

5) Databases. Two properties that it is normalised? (2 marks)
1 - There is no redundancy
2 - There is no repeating groups

6) SQL - Selecting Surname, Forename, Email (5 marks)
SELECT Surname, Forename, Email
FROM Loan, Book, Member
WHERE Loan.BookID = Book.BookID
AND Loan.MemberID = Member.MemberID
AND Book.Author = AuthorName author = "Lucas Bailey" AND Book.BookID = Loan.BookID

7) SQL Inserting (2 marks)
INSERT Book
Values ('name1', 'name2'...)

8) How to still keep table normalised (3 marks)
Said to create a new relation called BookCopy. Create composite key BookID,CopyID.

9) Why use hashing (1 mark)?
To keep data secure and to enable data to be searched quicker

10) Hash function (2 marks)?
Hash function applies hashing algorithm to provide a Hash value.

11) Collisions (2 marks)?
When two or more indexs have the same hash value. Can be resolved through open and closed hashing. Open is when the value is rehashed and placed in next available location. Closed is when there is a linked list.

On the whole, I think it was quite a reasonable paper. I do feel that the boundaries might be slightly lower.

My guess would be
A* = 71/100
A = 65/100

For the SQL INSERT code, it must take the form of either

INSERT INTO table VALUES (value1, value2, value3)
or
INSERT INTO table (column1, column2, column3) VALUES (value1, value2, value3)

You must always specify the table name because otherwise SQL does not know where to insert your data!


As for the complexity,
There was a multiple nested For loop, with the basic operation of 'If W1 = W2 etc'.
For each loop through, the current item was compared to every other item, so the current item was compared to 'n' items, meaning for each item the number of basic operations carried out was 'n'.

However, as this must be repeated for every item, and as their are 'n' items, the number of times the If statement will be repeated will be 'n' * 'n' as for every item it must compare it to every other item. And of course, n * n = n^2.
You could also verify that by showing that in your algorithm run through of 3 items, you carried out the IF W1=W2 operation 3 times per item, giving you a total number of 9 basic operations, and as n = 3, complexity must be O(n^2).

Hope that helped somewhat!

EDIT: @exam2k10,
I believe the expected answer for the first blank was something along the lines of 'develop an algorithm', so your answer of 'implement a turing machine' may be accepted, as technically implementing a turing machine implys that you are implementing an algorithm, but I think the answer to the second blank should have been along the lines of 'executing this program', so if you only wrote 'output' I don't personally think you'll get that mark :\