2009 HSC exam, Can anyone explain these questions to me? (1 Viewer)

[fakermaker]

Questions 19 and 20 of the Multiple choice I got wrong.

http://i.imgur.com/4pFID.jpg

For 19, I knew it was either B or D.

I chose D as I assumed that since it said the transmitter was wireless and receiver was ethernet, it was more correct that B, which stated that the transmitter was the NIC and reciver was ethernet cable (which is not in the picture above, although it is implied).

Does that mean that the Transmitter and Receiver are hardware devices and are the boxed elements in the diagram? Actually, B suggests that all three (transmitter, receiver and destination) are in boxes...is that how I'm supposed to read this diagram?

For Question 20, I have no idea how to read the SQL query. Can anyone explain why the answer is D?

 

[Gigacube]

Question 19
This is the communication system framework showing Jo's email travelling from her webmail account to Sam's webmail account. Take a look at page 36 of the IPT Syllabus. Compare the communication system framework in the syllabus with the one in the question. This might help you see why you got this question incorrect.

In this question:
Network Interface Card = Transmitter
Wireless = Medium

Therefore the answer is B.

Question 20
You should have learnt how to read an SQL query. It's very simple & it's not too late to learn.

SELECT - This lists the field names to be displayed. It is usually in the format tablename.fieldname although sometimes it is displayed as fieldname, fieldname, fieldname. It is usually displayed as fieldname, fieldname, fieldname if one table is used.
FROM - The tables that we want to collect & display data from. Usually the tables containing the fields listed in SELECT.
WHERE - This is the search criteria. Basically, we want the search to match a certain condition. In question 20 there is also AND. Even though it is on a new line it is still part of WHERE. I.e. we want the results to match the condition before AND & after AND.
ORDER BY - This isn't in the example but you are still expected to know this. It is the sequence in which the results are displayed. So you may have it asc(ascending) or desc(descending).

Let's go back to the question.

SELECT agent.name
FROM agent, residence
WHERE agent.agentno = residence.agentno
AND residence.residenceno = 342;

In this SQL query it is going to display the field name from the table agent.
We are using data from the tables agent & residence.
In this search condition it is telling us that there is a relationship between agent.agentno & residence.agentno. This means that the data in agent.agentno is the same as the data in residence.agentno. We also want to find something that matches residence.residenceno = 342.


What fact can be deduced from this query?
(A) All sales have the same agent.
This can't be true as agent.agentno = residence.agentno. The agentno in the residence & agent tables are the same.

(B) The sale has an agent numbered 342.
The results aren't displayed so we aren't 100% sure that there is. The query is trying to find if there is something matching the condition, residence.residenceno = 342. If something does match the condition then it will be displayed.

(C) The residence number attribute occurs in both tables.
The query contains agent.agentno = residence.agentno. This isn't true as the agentno attribute occurs in both tables, not the residence number.

(D) The residence table is not required to identify an agent
This leaves us with D which is correct because there is a relationship between the tables, agent.agentno = residence.agentno. The data in the field agentno is the same in both tables which means that to identify an agent we only need to use one of the tables.

I hope you understood all of the above. Good luck & feel free to ask more questions.

 

[hscishard]

^nice solution

though for the second question, it's not more on what's incorrect but what can't be deduced

 

[fakermaker]

Cheers, I'm still a little confused but I will watch some youtube videos and hopefully grasp the concept a bit better