Software Development

VCAA Exam Post Mortem

2014

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Case study

CASE STUDY INSERT FOR SECTION C
Please remove from the centre of this book during reading time.

Case study

Note - Figure 1 was a drawing of a happy cow getting a tag attached to her ear. The image was not produced by VCAA so I have not included it here. In any case, it added nothing to the case study, unless you love drawings of cows and ear tags. In that case, I substitute a reasonable facsimile. Now, stop crying. There there.

The Wide Hill cattle station is in Central Australia and measures approximately 80 km by 50 km. It is situated 200 km from a town of about 100 people. Currently, there is a herd of approximately 30 000 cattle on the station. The station provides cattle for a variety of markets. Some require cattle of a certain weight, while others require cattle of a certain age. All cattle in Australia are registered with the Australian Cattle Identification System (ACIS) and, when cattle are bought and sold, the information must be transmitted to a national database that is available online. All cattle producers have login access to this information. The cattle carry a radiofrequency identification (RFID) tag that can be scanned easily by an electronic reader. This provides a unique RFID code for each animal. The electronic reader can also record the current weight of each animal through a sensor set up in the cattle yards. The RFID tag provides many advantages to producers as all cattle in Australia can be traced.

Mike McIntosh, the station’s owner and manager, would like to expand the use of ACIS to help him work more efficiently and help him keep records that will provide information to improve his herd. He has identified a number of concerns he would like to address:

• Cattle from other stations get mixed in with Mike’s herd and he wants to use the system to quickly identify these cattle. Currently, he has to read the animal’s tag and check the RFID against his paper records to find out if it is one of his animals. If it is not one of his, he has to login to ACIS to find out where the animal belongs.
• Currently, Mike’s limited breeding information is kept on paper. In the future, Mike would like these records to be electronic. He hopes he will then be able to identify his best breeding stock and improve the quality of his herd.
• Mike weighs cattle for certain markets (which specify a specific range) and he hopes to be able to produce cattle that grow quicker, using this weighing and his electronic breeding records.
• Mike would also like to introduce some new breeding lines into his cattle and wants his records to keep track of these animals to see how they compare to the rest of the herd. If they do well, he will switch to these new breeding lines in the future.

Mike recognises that the remote location of his cattle station may present some problems. The only access to the internet is from a satellite connection based at the station’s homestead, where Mike’s office is. The only other form of communication around the station is via handheld radios. Mike has set up a wi-fi network of beacons around the homestead so that the buildings and cattle yards within 400 m of the main house have wi-fi available.
The weighing and scanning set-up is portable and can be moved to any one of six yards located around the station as well as the main homestead yards. However, the only way of communicating with Mike’s office is through a simple radio voice system when Mike is away from the homestead and out of wi-fi range. He is considering using a satellite system to transfer data to and from the homestead’s computer.

Mike would like to have a new software solution that will scan an animal’s RFID tag and enter its weight into his records while he is using a tablet computer in any of his cattle yards. He would then like to be able to upload these records onto the homestead’s computer.
He would also like the following information to be stored and displayed on the tablet:

• whether each animal belongs to him
• where each animal was born and its parentage
• the age of each animal
• a comparison of each individual animal’s weight with the average for the herd (at that age)
• any other relevant information about the cattle (e.g. how many calves each cow has produced)

On viewing this information, Mike can then make a decision as to what to do with each animal and direct his station workers accordingly. As he has approximately 30 000 cattle on the station, these decisions need to be made quickly. If he finds an animal with an excellent growth rate, for example, he may wish to keep it for future breeding.

Mike has contracted Nicole to design and develop his new Cattle Station Software (CSS) to provide all the extra information. The new software must be able to provide communication between his office in the homestead and the portable weighing and scanning system when it is used at each of the six cattle yards around the station.

END OF CASE STUDY INSERT FOR SECTION C

Instructions for Section C

Answer all questions in the spaces provided. Remove the case study insert and read all the information provided before you answer these questions. Answers must apply to the case study.

C1

(4 marks)

Question 1 (4 marks)

Nicole’s office is 600 km from the Wide Hill cattle station. She needs to begin the analysis as soon as possible. There are four techniques Nicole could use to help her with her analysis: observation, interviews, questionnaires and reviews of Wide Hill’s software documentation.
Outline a major strength of each of these techniques. [3 lines per topic]

Hmmm. Does the question mean a major strength for Nicole, 600km away? Answers should always relate to the case study, but the question does not focus on Nicole's special circumstances. Play it safe and focus on this situation, I'd say.

Observation

• direct, first-hand, primary evidence can be obtained. All other secondary evidence must be filtered through other people's interpretations and choice of what to report.
• can get a better understanding of the realities of the context of the solution;
• direct observation may unearth facts that farm workers had considered self-evident and unworthy of mention. For example, farmhands know that semi-wild cattle are huge and nasty, so noone should get near them without a steel enclosure; a city-girl like Nicole might have been planning a system that involved treating cattle like they were friendly, tame dairy cows. Or Nicole may realise first-hand the rigors that equipment must cope with in 50 degree temperatures and clouds of choking dust - something that the workers may not have mentioned since they took it for granted.

Interviews

• can get more detailed information than would be likely if it had to be written down
• can elicit personal feelings and reactions. People (especially men) are much less likely to open up emotionally in writing compared with face-to-face conversation.
• the exchange is more dynamic and responsive - planned questions may be modified in the light of previous answers, and follow-up questions asked after an unexpected or illuminating answer
• the personal touch may 'loosen up' up uncooperative subjects and make them more responsive. These people may easily refuse to fill in a questionnaire, but will feel sheepish about rudely refusing to talk directly to a visitor.
• body language, tone of voice, hesitation, and gestures can be valuable clues to deeper unexpressed truths behind a person's words. Irony, sarcasm, reluctance, emotion can all be expressed and detected.and review

Questionnaires

• for Nicole, these are easy to accomplish. People need not travel to a remote location. Questionnaires can be handled by mail or email.
• are quick to fill in, so respondents are more likely to comply
• can gather a lot of information from large groups of people quickly, cheaply and easily
• responses with restricted sets of answers are easy to enter into an information system

Reviews (of software documentation)

(Assuming that this refers to user documentation and not internal documentation...)

• the documentation would tell Nicole what the existing software was capable of (i.e. scope)
• it could reveal areas of functionality that need to be improved, removed, or added

Most students handled the first three stated techniques well; however, many students misinterpreted ‘Reviews’. The stem of the question stated one of the techniques that could be used to help with the analysis was ‘reviews of Wide Hill’s software documentation’, that is, the technique would review the current documentation, not the software. Many students assumed the reviews had already been conducted and this was incorrect.
It is important that students remember that responses in Section C must apply to the case study. So when describing the strength of a technique, it was expected that the strength would be applicable to Wide Hill.
The following is an example of a high-scoring response.
 Observation Can see the current system at work and detect problems that the cattle station’s staff may not see
 Interviews Able to directly know what Mike and the station workers are having trouble with, and discuss their options with Nicole
 Questionnaires Allows Nicole to quickly obtain information about the cattle station’s staff’s problems
 Reviews Allows Nicole to very carefully examine the current system, outlining flaws that observation cannot

Average mark 57%

C2

(4 marks)

Question 2 (4 marks)

As part of her analysis, Nicole has begun a data flow diagram (DFD; Diagram 3) and a context diagram (Diagram 4).

Diagram 3: Data flow diagram (DFD)

Diagram 4: Incomplete context diagram

Using the information in the DFD, complete the context diagram by writing the labels for A, B, C and D below. [1 line each]

A - Manager

The DFD shows a report being sent from the 'prepare cattle report for manager' process. It must logically be going to the manager external entity.

B - Portable weighing and scanning set-up

The only external entity that provides weight information must be the portable scales.

The examiner's report said B = cattle. That's an odd one!

C - Cattle condition

If you find "cattle destination" in the DFD, you'll notice that the only other data travelling with it is cattle condition.

D - TagID + cattle destination

Something is being sent to the ACIS external entity. Look at the DFD and find that the process for 'format data for ACIS database' is sending TagID + cattle destination - and it must be going to the ACIS database.

Remember -

• The CD incorporates all of the DFD's information, but hides system processes and data stores within a single system circle.
• Tip - in the DFD, draw a line to enclose the CSS system's processes and exclude the external entities.
• The CD and DFD both show the same external entities.

Responses to this question were quite poor. Students should be encouraged to use the data flow diagram to assist in formulating accurate responses, particularly with respect to labelling conventions. Further emphasis should be given to the teaching and learning of this topic.

Average mark 38%

C3

(5 marks)

Question 3 (5 marks)

Nicole decides that, when each animal is weighed, if its weight is below 50 kg or over 500 kg, the software solution will seek confirmation of that value before it is entered into the animal’s records. Animal weights are recorded to one decimal place.

a. What type of validation is this? 1 mark [1 line]

Range check.

Do not ramble with statements like "This type of validation is known as a range check." We all know what the question is. You don't need to repeat it.

The correct validation type was range check.

Average mark 60%

b. Five different items of test data are required to test this weight function. The first item of test data has been provided in the table below.

Complete the table with the remaining four items. 4 marks

Good test data thoroughly tests boundary conditions where software behaviour is expected to change. That's where most SD exam logical errors lurk.

(The examiners' answer is the same as mine. Test 3 can be any value 0ver 50 and less than 500.)

Students are reminded that when testing a specific range, it is important to test the boundaries and not to test the same thing multiple times.

Average mark 77%

C4

(4 marks)

Question 4 (4 marks)

Nicole decides that the Cattle Software Solution (CSS) will store its data in a single file. This file will be regularly searched using the ACIS code. The file contains only one type of record and includes the field names given in the table below.
From the following list of data types, select the most appropriate data type for each field name and its accompanying description in the table below. An example has been provided.

integer floating point Boolean character string

Thank Dog the SD exam did not fuff up the interpretation of the logical true/false Boolean field as the ITA exam did. Bravo!

Students generally answered this question well; however, many overlooked the description of ACISNo. The description indicated that it was a 16-digit number with the fourth digit blank. With this condition, it could not be an integer.

Average mark 75%

C5

(1 mark)

Question 5 (1 mark)

When an animal’s ACIS code is identified, a number of steps are undertaken.

"A number of steps IS undertaken."
The verb must agree with the subject of the sentence, "A number" (singular) and not "steps" (plural).
Wrists out, VCAA. Slap. Now, be good.

One step is represented by the algorithm below.

Search station records using ACIS code
If Found then
   ACISFound True
Else
   ACISFound False
   Display ‘This animal does not belong to this station’
Endlf

What is the name of this type of check? [1 line]

Existence check.

Well - that was easy.

In SD U4O1, you only need to know validation checks for: range; type; and existence.
And range check had already been examined in C3a.

The correct validation type was existence check.
Many students were unable to identify the types of validation occurring in this question and in Question 3a. It is important that students apply validation during school-assessed coursework. It is also recommended that they include an algorithm for each of the three types of validation listed in the study design, in their glossary.

Average mark 50%

C6

(10 marks)

and

Question 6 (10 marks)

Mike wants to know how each animal compares to others of its age before deciding whether he wants to keep it for breeding or sell it. Cattle between six months and 24 months are broken into three age groups:

• AgeGroup = 1 is for cattle older or equal to six months and less than 12 months
• AgeGroup = 2 is for cattle older or equal to 12 months and less than 18 months
• AgeGroup = 3 is for cattle older or equal to 18 months and less than 24 months

On start-up, the program will compute the average weight of the cattle in each of the above groups so that Mike can compare an individual animal’s weight with the average weight. The algorithm below calculates the CattleAge in months and then the age group of each animal. If the animal is too young or too old, an appropriate message is given.

Begin    AgeGroup 0    CattleAge Difference in months between current date and date of birth    If CattleAge < 6 Then       Display ‘Cattle Too Young’    EndIf    If CattleAge >= 6 And CattleAge < 12 Then       AgeGroup 1        Display ‘AgeGroup = 1’    EndIf    If CattleAge >= 12 And CattleAge < 18 Then      AgeGroup 2       Display ‘AgeGroup = 2’    EndIf    If CattleAge >= 18 And CattleAge < 24 Then      AgeGroup 3        Display ‘AgeGroup = 3’    Else        Display ‘Cattle over 24 months’    EndIf End

a. The following table contains a subset of the test data that was used to test the algorithm before coding it.

Complete the table for each date of birth given. An example has been provided.
For the testing, Current Date = 14/11/2014 was used. 6 marks

Students were able to identify expected output, but many students assumed that the message ‘Cattle over 24 months’ would overwrite the age group message rather than two messages being displayed. Also, many students confused display the text ‘AgeGroup = 1’ with the variable ‘AgeGroup’ and so assumed the output would be ‘1 = 1’.

Average mark 56%

b. Explain the major error in the algorithm. 2 marks [4 lines]

Previous 'true' tests are ignored by the final 'else' statement, which should only test ages that have not already been proved true. So, for example, if the test for age=10 is true for an earlier test, it is again tested for ages 18-24, fails, and the 'Cattle over 24' results.

In all age groups other than between 18 and 24 months, the correct message is displayed along with an incorrect message saying ‘Cattle over 24 months’.
Students needed to ensure that they commented on the incorrect message being displayed and when that message appeared. A small number of students said there was no condition equal to 24 months; however, this was not the major error in the algorithm.

Average mark 30%

c. Explain how to fix the error in the algorithm. Where a line(s) of code needs to be rewritten, write the line(s) in full. 2 marks [9 lines]

The final ELSE statement needs to be separated from the test for ages 18-24 because it's catching all cases that are not aged 18-24. If cattle have already been categorised, they should not be tested again.

Change the end of the code to...

If CattleAge >= 18 And CattleAge < 24 Then
     AgeGroup 3
       Display ‘AgeGroup = 3’
End if

If CattleAge > 24 Then
     Display ‘Cattle over 24 months’
EndIf

Don't waste time re-writing all of the code. Make it clear that you know where the error is and re-write that part only.

I hope the markers accept valid variations like SELECT CASE. Most languages have a SELECT CASE facility, which obviates messy IF/ELSE construct errors.

Another meatybite question. Me gusta.

There are a number of ways of fixing the error. The simplest way was to remove the ‘EndIf’ and add an additional ‘If/Then’ condition.

If CattleAge >= 18 And CattleAge < 24 Then
     AgeGroup 3
     Display ‘AgeGroup = 3’
EndIf
If CattleAge >= 24 Then
      Display ‘Cattle over 24 months message’
EndIf

Most students were unable to explain how to fix the error or write the lines of code needed. Students should practise algorithms for a range of unseen scenarios throughout the year.

Average mark 30%

This was a tricky task. At first I could not see it, and it took me a while to isolate the problem with a deskcheck.

Yes, folks. Deskchecks are not just to keep teachers and examiners happy - they actually work with real programming problems!

First, you needed to calculate the ages of each test cow.

For the record - the ages were 22, 10 and 3 months respectively.

I counted on my fingers. You might have used higher mathematical cognitive skills to achieve similar results... I wish I had some of those.

Then, using each age, step through each line of the pseudocode. Draw lines to create 3 test data columns... (I've abbreviated text a bit so it would fit in a narrow space. "X" means "skip this")

DESKCHECK
Pseudocode	14/1/2013	14/1/2014	14/8/2014
AgeGroup 0	Age=0	Age=0	Age=0
CattleAge Difference in months	Age=22	Age=10	Age=3
If CattleAge < 6 then	false	false	TRUE
Display ‘Cattle Too Young’	x	x	show it
EndIf	land here	land here	OK
If CattleAge >= 6 And CattleAge < 12	false	TRUE	false
AgeGroup 1	x	age=1	x
Display ‘AgeGroup = 1’	x	show it	x
EndIf	land here	OK	land here
If CattleAge >= 12 And CattleAge < 18	false	false	false
AgeGroup 2	x	x	x
Display ‘AgeGroup = 2’	x	x	x
EndIf	land here	land here	land here
If CattleAge >= 18 And CattleAge < 24	TRUE	false	false
AgeGroup 3	Age=3	x	x
Display ‘AgeGroup = 3’	show it	x	x
Else	x	land here	land here
Display ‘Cattle over 24 months’	x	show it	show it
EndIf	land here	OK	OK

Obviously in real life you don't rigorously fill in every cell. You make a note in the cells of consequence.
If you still haven't found the logic bomb, then you go back and annotate every cell!

C7

(2 marks)

Question 7 (2 marks)

Mike wants to use a tablet to record the weight of the cattle. Nicole tells him that the tablet has 512 MB of primary storage (RAM) and 16 GB of secondary storage. She could go to 32 GB of secondary storage, but she cannot alter the 512 MB of RAM.

Apart from cost, outline the technical difference between the two types of storage used on the tablet and how this may affect access to the data stored. [5 lines]

Data access speed.

RAM (random access memory) is used during the execution of a program to hold the program's executable code and the data it is using during execution. It is very quick to read and write to RAM. Primary storage is volatile - its contents are lost when the program or the device is shut down. If the program plus its necessary runtime variables, arrays etc cannot fit in primary storage, the program will either crash, fail to start, or resort to swapping data in and out of slow secondary storage to get enough room to run the software.

Secondary storage (e.g. hard disk, SSD, SD card) is non-volatile storage used to permanently store executable code and data between program executions. Data here can also be accessed by a running program. It is usually much slower to access than RAM, which is why computers will little RAM will run slowly as they resort to using secondary storage page files to act a slow alternative to primary storage.

It's interesting to see that the examiners are no longer spelling out "MB" and "GB" units. We're all growing up!

It wasn't so long ago that we stopped capitalising the "i" in "internet."

These are significant milestones, folks!

Students struggled to provide clear and technically accurate responses to this question. The question had two parts and many students missed the second half of the question. Students are encouraged to read and re-read the question throughout the examination and then do the same for their response.
The following is an example of a possible response: Primary storage is non-permanent memory used to hold temporary data and is accessed faster than secondary storage. Data in secondary storage is slower to access but data is stored permanently even after the device is turned off.

Average mark 35%

C8

(2 marks)

Question 8 (2 marks)

Each record contains less than 200 bytes of information. It is expected that the software solution will initially hold 30 000 records and will eventually hold a maximum of 100 000 records.
To help with planning, Nicole needs to estimate the range of the file size, from minimum to maximum size, in terms of megabytes.
What would be the minimum and maximum expected file sizes?

Minimum expected file size [3 lines]

[Three lines for each answer? Don't tell me the examiners expected another unrequested justification!]

6MB

(200 * 30,000) / 1,000,000

Maximum expected file size [3 lines]

20MB

(200 * 100,000) / 1,000,000

All right! Settle down, petals. Chris! Put down that chair. I don't CARE - just put it down. I know this could get messy. The figures shown above assume there are exactly 1,000,000 bytes in a megabyte, obeying the new official IEC (International Electrotechnical Commission) redefined definition of 'megabyte' as exactly 1,000,000 bytes (which nearly everyone in the industry ignores).

Were the examiners instead thinking of the new (horrible) mebibyte (MiB) unit (1 mebibyte = the traditional 1,046,576 bytes), in which case the answers would have been 5.7 and 19.0 respectively?

It will be fascinating to see what happens if the markers reject an answer of 19.

As the IEC says, "Time will tell if comfortable reading will prevail over technical accuracy."

Minimum expected file size 5–6 MB
Maximum expected file size 19–20 MB
Students were asked to estimate the minimum and maximum file sizes in megabytes, but many gave their answers in bytes or kilobytes. Students are reminded to read questions carefully. Students who did answer correctly often showed their working and conversion.
Either 1024 kilobytes or 1000 kilobytes could have been used.
An example of a calculation follows:
200 × 30 000 = 6 000 000 bytes
1 MB = 1000 KB = 1 000 000 bytes
6 000 000/1 000 000 = 6 MB

Average mark 35%

C9

(6 marks)

Question 9 (6 marks)

For the software solution to be successful, rapid searching of the records on the ACIS code is essential. Nicole suggests using a random access file stored on the homestead’s computer and sorted on the ACIS code. Also, with 100 000 records, it would be best to read a record only when required and modify it when required.

Adam, a programmer friend, suggests using a sequential file sorted on the ACIS code. When the program starts up, it will load all the data from the homestead’s computer onto the tablet and all records will be stored in a one-dimensional array that will then be searched. When the program is shut down, the file will be rewritten back onto the homestead’s computer.

Hang on one cotton-picking minute. Did you say the records will be stored in a one-dimensional array? How would THAT work? There are 5 fields (see Q4). Would the fields in each record be concatenated to form a single string? And then parsed for processing. And then again concatenated for storage? Or would each array index contain a single field, requiring 5 array accesses to gather 1 record? That would make sorting a massive pain! Alan, the silly duffer, should have used a 2D array. Fortunately this does not seem to affect the marking of any questions. I'm not sure whether or not the examiners meant Adam's method to have this serious weakness...

This question was poorly answered by the majority of students. Most students picked up on the key words ‘random access file’ and ‘sequential file’ in the question and wrote lengthy descriptions of these file types; however, the question asked students to describe the advantage of each complete method outlined. So students should have taken on board the full description of file type, file transfer and updating data.

a. Describe one advantage of Nicole’s method. 2 marks [6 lines]

• It consumes relatively little RAM on the tablet, since the data does not need to be copied to the portable device.
• The system would start up more quickly since the large data transfers of Adam's method would not be necessary.
• Keeping the random file's records sorted will be vastly quicker than Adam's sequential file method.
• A record could be retrieved all at once, as a unit, compared to Alan's 1D array which requires 5 operations to gather the fields for a record.
• Once a record is written to a random file, it is saved. Sudden data loss would not lead to lost data, as it would if the change were stored in a volatile RAM array.

Nicole’s searching method ensured that the file was always accurate and up-to-date as it accessed a record only when required.

Average mark 10%

b. Describe one advantage of Adam’s method. 2 marks [6 lines]

• Once the data has been loaded from the homestead's computer onto the tablet, data access speeds would be far greater than retrieving them individually over a slow radio internet connection.
• Once the data has been loaded, the tablet could be used productively even if the internet connection were lost for a while. Once the link was re-established, the modified data could be synced.

Reading data (locally) from the tablet is faster than reading it over a network and continually having to read/write back. In addition, work can continue when out of wi-fi range.

Average mark 20%

c. Suggest an alternative method that may overcome a problem with either Nicole’s or Adam’s method. Justify your suggestion. 2 marks [6 lines]

- A copy of the data could be permanently stored in the tablet's secondary storage (e.g. SD card). When changes to the data occurred (either using the tablet or on the homestead computer), the changes could be synced wirelessly. Since changes would be relatively small, syncing would not take much time nor bandwidth.

This would overcome the Nicole's potential problem with slow access speeds, and Adam's potential problem with RAM shortage.

Note: the tablet has 512MB of RAM [see Q7], so even the biggest data file (20MB) should still comfortably fit into the tablet with the OS and CSS program using Adam's method.

- Alternatively, Adam's slow sequential file sorting problem could be alleviated by using an index to keep track of records' order without having to physically more records in RAM.

- Adam should use a 2D array so a record's fields could more easily be managed and accessed programmatically.

An alternative to these methods would be one that combines elements of each to ensure ease of use and speed.
The following are examples of high-scoring responses.
Have the data stored as a random access file on the tablet itself and backup the data to the computer at the end of each day for security and transmission to the ACIS database. This method combines the efficiency of Nicole’s method with the convenience of Adam’s method and adds a redundancy backup.
The files could be sent to the tablet each day and then be access from a random access file while needed, keeping them secuer and improving speed. At the end of the day they would be sent back to the homestead computer.

Average mark 15%

C10

(2 marks)

Question 10 (2 marks)

Nicole is also concerned that as the number of records increases, it will take more time to search these records.
What would be the effect on the number of records read (on average) if the total number of records increased from 32 000 to 64 000 (doubled) using

Hang on. This just doesn't make sense.
Let's simplify the second sentence to...
- What would be the effect on the number of records read if the total number of records doubled using a XXX search.

Is this suggesting that using a particular search would double the number of records? Can't be.

So does it mean - deep down in its befuddled syntax...
- If the number of records doubled, what would be the effect on search times using a XXX search?

Or does it mean...
- If the number of records doubled, how would that affect the number of records that would have to be read to carry out a XXX search.

The first sentence in the question is definitely focused on search times.
The second sentence is (maybe) concerned with the number of records that would have to be read to carry out each type of search.

Obviously the two things are related, but - to me - the question does obfuscate what key knowledge it's trying to assess. It's a shame the question was so confusingly language-mangling.

- a linear search [3 lines]

If the number of records doubled, the maximum number of records read -and the consequent maximum search times - would also double.

- a binary search? [3 lines]

If the number of records doubled, the number of records read - and the consequent search times - would not be significantly increased. Doubling the number of records may only require a few more reads.

This is - I think - what the examiners wanted to hear.

The following is an example of a possible response:
 a linear search
The average number of records read would double (from 16 384 to 32 768).
 a binary search
The maximum number of times a record would need to be read would increase by one (from 15 to 16) as only the record in the middle of the list is read because the list is halved each time.

Average mark 45%

C11

(2 marks)

Question 11 (2 marks)

Mike is still concerned that the tablet may take too long to transfer files containing 100 000 records. He wants Nicole to design a simple test that will show him whether the tablet can transfer the data between the homestead’s computer and the tablet within a given time and under stated conditions.

Outline a test that Nicole could use to demonstrate this. [6 lines]

Create a test file with 100,000 dummy records. Take the tablet an agreed distance from the homestead computer. Start a stopwatch. Start transferring the test file from the tablet to the homestead. Time the operation. To be complete, then measure how long it takes to send the data back from the homestead to the tablet.

Ummm, is this question inconsequential, or am I missing something significant?
A year 7 student could answer this.

In general, students were able to identify the need to measure the file transfer time. However, it is important that students pay attention to the task word in each question. For full marks students needed to provide the procedure(s) for testing at least one file size under specific test conditions, indicating a technique for measuring transfer time. The response needed to relate to the specific details in the question.
The following are examples of high-scoring responses.
Nicole could create a file with 100 000 simple records. With the tablet under the stated conditions. Nicole could send the file multiple times to the tablet recording how long each copy takes. The average copy time can then be calculated.
Setup the stated conditions. Run a program that starts a timer and begins transmitting the data from tablet to computer but alerts Nicole if it exceeds a given time. Repeat the test with different conditions and perhaps different time restrictions.

Average mark 55%

C12

(3 marks)

Question 12 (3 marks)

Nicole has been working on the interface for the CSS. She knows that when Mike is weighing the cattle, he will be required to make split-second decisions based on the information presented to him by the software. This makes the interface design very important as Mike will need all relevant information in front of him in order to make those decisions.

Nicole has produced the following designs for the Weigh Module of the ID screen for each animal. She is currently deciding whether to include visual representations of some information (Option A) or to just present the data in text and numbers (Option B).

(Click to see image full size)

Which option would you recommend? Justify your answer.

Recommendation [1 line]

Option A

Justification [6 lines]

It's obvious that human brains interpret analogue and pictorial information far more quickly and with less chance of error than they do when it's written or numeric. A glance at a graph gives more instant - albeit less detailed - information than a paragraph of writing or a table of numbers.

Since speed is of the essence in Mike's case, the graphical, iconic presentation of the information would be valuable. The slight loss of details would be a trivial cost if he could get enough vital information with a quick glance.

Why do you think road signs use simple images with minimal writing?

Try describing that information in words for motorists travelling at speed.

Students could have recommended either interface option but needed to provide a detailed response as to why that option was recommended. Many students provided only one reason as to why that option was recommended. Students should ensure they take note of the mark allocation as this will often give a guideline as to the depth of response required.
A possible response could have been: Option A – Mike needs a visual representation of growth. The graph will provide much clearer information that does not require interpretation or prior knowledge, and anyone could use it. It could contain the average growth tracked on one line with the animal’s growth on another to determine good or poor growth. The map will allow Mike to quickly gauge the location of the animals (prior to roundup) and determine whether they should be relocated based on pasture available in each paddock and whether the animals need to put on weight or not. This information is clear and much more easily understood.

Average mark 50%

C13

(6 marks)

Question 13 (6 marks)

Hardware item 1 [1 line] Modem

Role [3 lines]

Converts digital signals to and from analogue signals for the purpose of transmission over non-digital media.

Hardware item 2 [1 line] Satellite dish

Role [3 lines]

Converts digital or analogue data into radio signals for transmission to a communications satellite in a geostationary orbit around the earth.

Perhaps also... a cable, to carry data from the computer to the modem and to the satellite dish.

You would not want to use handy but inessential items such as routers, switches, mouse mats etc. It's also best to avoid the bleedin' obvious things like "a computer", "a CPU" or "a power switch."
Use common sense. Identify what the question wants you to prove an understanding of - and give them what they're hoping for.

A range of answers was accepted, including modem, router, satellite dish, etc.
The following is an example of a high-scoring response.
Hardware item 1 - Satellite Dish
Role - Allows the users of the network to access the internet using satellite technology
Hardware item 2 - Router
Role - To connect the local area network of Wide Hill homestead to the wide area network (WAN) that is the internet and through that connect to the ACIS database.

Average mark 58%

b. Explain one effect on Wide Hill if one of the items identified in part a. failed. 2 marks [3 lines]

• Modem failure - data could not be sent to or received from the satellite dish.
• Dish failure - data could not be sent from or received to the homestead modem and computer.
• Cable failure - data could not be sent to the modem for transmission via the satellite dish.

In part b, be sure to identify which of the 2 hardware items you are referring to!

Students are encouraged to highlight key words as it was important to recognise that the response required an explanation of the effect on Wide Hill. Simply stating ‘unable to connect to the internet’ was not sufficient for two marks.
The following is an example of a high-scoring response.
If the router failed the Wide Hill homestead computer will not be able to connect the network to any other network including the internet and through that the ACIS database.

Average mark 60%

C14

(4 marks)

Question 14 (4 marks)

Mike feels that a satellite connection is the only option for connecting the outlying cattle yards. Nicole suggests that this would be a very expensive option and that Mike should consider using microwave. Mike says that he has heard there are some issues with using microwave as a method of transmitting data.

State two characteristics of microwave transmission that Nicole needs to explain to Mike before installing it on Wide Hill cattle station. Explain the relevance of each of these characteristics for the cattle station.

Characteristic 1 [1 line] It operates on a line-of-sight.

Explanation [3 lines]

If the signal is blocked by an obstruction (like a hand in front of the beam from a torch) the signal is lost. Unlike radio, microwave signals do not penetrate obstacles.

So the transmitter must be placed high enough at the homestead to clear all hills and buildings between itself and the location of the receiver.

Characteristic 2 [1 line] It's narrow and directional.

Explanation [3 lines]

Unlike radio waves which (usually) travel in all directions from an emitter. Microwave signals travel as a narrow beam in a single direction - like a laser beam.

So, the microwave dish will need to be moveable in order to aim at its intended data recipient.

I think this question will have caught a few students and teachers off-guard.
Microwave has never received this sort of attention in an exam before!
I predict the state average for this question will be about 25% !

The peculiar drum-shaped objects you see on the tops and sides of tall buildings are microwave dishes, high up to clear obstacles and aimed precisely at a single destination dish.

Many students struggled to respond with the detail required and with technically accurate information. It was clear that many did not know a great deal about microwave transmission. The most appropriate characteristic to discuss was ‘interference of signal’. Microwave signals need a line of sight between the cattle yard and the homestead and, in addition, weather conditions may interfere with the signal. A range of responses was accepted, but not cost.

Average mark 28%

C15

(3 marks)

Question 15 (3 marks)

Nicole is concerned that if the hardware fails or is destroyed by accident, all of the cattle station’s records would be lost and so would years of information. Mike suggests that the records be copied onto a DVD each week and stored in his filing cabinet.

a. State one potential fault with this method. 1 mark [2 lines]

• DVDs deteriorate with age and may lose data.
• DVDs are easily scratched and become unreadable.
  • Don't just say DVDs are easily scratched. That in itself is not a fault in terms of data backup. Cats are also easily scratched, but that does not impede their catability™. The fact that DVD scratchability leads to unreadability is the fault. Make sure you finish your train of thought and explain the relevance of your answer.
• Storing the backup DVDs in the same place as the original data will be dangerous. If the original data is stolen or destroyed by fire/flood/ninja attack etc, the backups could easily suffer the same fate.
  • Better to avoid the 'ninja attack' argument in a real answer. The sense of humour of markers is vastly over-estimated.
• Backing up only weekly could still lose up to 6 days' data in a disaster.
• DVDs' data capacity is not terribly high in modern terms. Weekly backups of 20MB would fill a DVD in... 4.5 years. OK. You realise this is not really important in this case. Remember that your answers must to be relevant to the case study. Cross this answer out and find a more relevant response.

Be sure to pay attention to all parts of the question. Fixating only on the qualities of the DVD might make you forget to address the issue of the storage in the filing cabinet and the weekly schedule! When you think you've finished answering a question, READ IT AGAIN and discover what you missed the first time. In SD exams, it will be there.

Students tended to focus on the DVD being scratched and thus losing data. A more appropriate response would have discussed the backup method identified – storing the DVDs in a filing cabinet. Any data in a filing cabinet could be stolen or destroyed by natural disaster. This method offers little data protection.

Average mark 40%

b. State a better method. 1 mark [4 lines]

• Daily incremental backups to a portable hard disk with full weekly backups. Store them offsite. Test the backups for accuracy and completeness.
• Backup to the cloud daily.
• Even better, set up a "trickle" backup to the cloud that uploads new and changed data as soon as it appears.

You only get 1 mark for this. Don't write an essay about it.

When stating a method, students should have considered the storage media, type of backup method and storage location, such as cloud-based and fireproof safe. Some students also indicated who was responsible for the backup. Many suggested multiple DVDs or a hard drive, or storing off site (which was not practical in a remote location), without providing additional details.

Average mark 50%

c. Nicole also suggests that when one of the cattle is sold and it has not been used in the breeding program, its record should be removed from the main records and stored in a different file that can then be removed from the computer and kept in case it is ever required.

State the name of this process. 1 mark [1 line]

Archiving.

That's it. No more.
You get no more marks for saying, "The name of this process is archiving."
Nor do you get bonus marks for showing off your knowledge of how archiving differs from backing up.
You just waste time and ink.

Archiving
The relevant key knowledge specifically identifies security, archiving, backing up and disposing of files as procedures and techniques for handling and managing files (Unit 4, Area of Study 1).

Average mark 60%

C16

(2 marks)

Question 16 (2 marks)

Each time the cattle is rounded up for weighing, Mike employs extra staff on-site. The extra staff are usually a mix of contracted farmhands and backpackers. This arrangement works well for Mike, who provides the staff with free access to his internet connection via wi-fi. Recently, Mike has had to bring in more staff than in the past as his herd has grown.

With a large number of people accessing the internet connection, describe a conflict that might arise among the users of the system and outline what Mike could do to minimise this conflict. [9 lines]

"contracted farmhands" - is this a term most 16-17 year old students would know - especially if ESL? I seriously doubt it.

The limited bandwidth could easily be used up so some people cannot connect. This could cause hostility between those who cannot connect and those who are obviously using more than their fair share of the bandwidth with large or frequent downloads.

• Mike could inform all users that they have a responsibility to use the bandwidth moderately and not monopolise it so others cannot also enjoy the facility. (Education)
• He could enforce a rule that bandwidth abusers will lose wi-fi privileges. (Sanctions)
• He could give each user a unique login name/password and allocate each account a bandwidth quota.
• He could revoke wi-fi access for the cows and allot it to the farm hands. After all, they just get on to CowBook and moo endlessly about how their bulls are ignoring their individual girlish bovine needs...

Maybe not the last one...

Many students failed to identify the conflict that might occur, simply stating that the internet would slow down. A more appropriate response would have included the following: disgruntled employees frustrated as they can’t get their jobs done, farmhands complaining to Mike about the lack of ‘free internet’, etc. Students, however, were able to come up with a variety of methods to minimise the conflict. A range of reasonable responses were accepted.
The following is an example of a high-scoring response.
The staff many complain that with all the staff accessing the internet via the Wi-Fi, that the networks bandwidth many be taken up and therefore its speed many reduce significantly. This could be fixed by setting data limits for those connecting to the network via login so no member of staff uses too much or slows the network down as much.

Average mark 50%

The 2014 SD exam in review

Another solid job. Well balanced, clearly written (on the whole), fair. It gives scope for the top achievers to show their stuff (e.g. the microwave question in C14 and the explanations of sorts in B2). A few questions were inexplicably basic (A2, A4, C11) but most were suitably challenging (e.g. A7, A8) and several were creative. And kudos for the added weight given to writing pseudocode (B3). More please!

Well done, examiners.
You have done well.

Suggestion - get whoever writes the SD exam and put them on a bus to the ITA exam writing office to show them how it's done.