[Year 12 SofDev] RE: Database question and confusion
Russell Quinn
QN at boxhillhs.vic.edu.au
Wed Oct 15 14:10:07 EST 2008
Another excellent reason for having a properly
defined course. Our current VCAA statements
only breed confusion and inefficiency. They wast
out time and there students time, esp. when there
is precious little time to spare. But no
one ever seems to listen or respond.
Russell Quinn
Mailto: qn at boxhillhs.vic.edu.au
From: sofdev-request at edulists.com.au
Sent: Tue 14/10/2008 1:00 PM
To: sofdev at edulists.com.au
Subject: sofdev Digest, Vol 44, Issue 4
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Today's Topics:
1. RE: Database question (Quentin Lydall)
2. Re: Database question (Mark Kelly)
3. Re: Special thanks to Associate Professor Steven Bird
(Kevork Krozian)
----------------------------------------------------------------------
Message: 1
Date: Tue, 14 Oct 2008 12:10:07 +1100
From: "Quentin Lydall" <qly at beaconhills.vic.edu.au>
Subject: RE: [Year 12 SofDev] Database question
To: "Year 12 Software Development Teachers' Mailing List"
<sofdev at edulists.com.au>
Message-ID:
<AFC3563D81D1044097735D5F6A3DBBE5014D7B6E at valley02.Beaconhills.beaconhills.vic.edu.au>
Content-Type: text/plain; charset="UTF-8"
I agree. Students should understand normalization, primary and foreign keys, lookup tables, data types and their properties, etc. There just is a fundamental logic error in the formulation of this answer, in a database context. Maybe it was done late at night..
Quentin Lydall
Head of ICT
Beaconhills College Valley Campus
30-34 Toomuc Valley Road,
Pakenham
3810
Phone: 1300 002 225 Extn 3016
Please consider the environment before printing my email
-----Original Message-----
From: sofdev-bounces at edulists.com.au [mailto:sofdev-bounces at edulists.com.au] On Behalf Of Steven Bird
Sent: Tuesday, 14 October 2008 11:58 AM
To: Year 12 Software Development Teachers' Mailing List
Subject: Re: [Year 12 SofDev] Database question
On Tue, Oct 14, 2008 at 11:13 AM, Adrian Janson
<janson.adrian.a at edumail.vic.gov.au> wrote:
> Yes – quite correct. My students spotted this as well. The x5 is not
> required.
There's some other problems though. A database with 20,000 customers
should have one or more indexes to support efficient retrieval, and
these take space. Nightly dumps take space as well. If the question
is getting at how much disk space we should budget for, these factors
are relevant.
It would be bad database design to store postcode and suburb with each
customer record (cf [1]). Instead a customer record should contain a
foreign key to a table of postcodes, e.g. a subset of [2]. We're told
the company only has sales in a "local area", so perhaps we'd only
have to deal with a dozen postcodes. That table would be a constant
size overhead which is easy to compute, and the foreign key would be a
short integer (e.g. TINYINT).
The question treats a database as if it was a spreadsheet, and only
requires students to know the relative sizes of characters, bytes, and
bits.
It would be good if students learnt about normalization and the
importance of avoiding duplication in a database. It would also be
nice if they learnt what Unicode is, and that 1 character != 1 byte.
[1] http://en.wikipedia.org/wiki/Database_normalization
[2] http://www1.auspost.com.au/download/pc-full.zip
-Steven Bird
http://www.csse.unimelb.edu.au/~sb/
> A database for an online marketing company keeps records of all customers
> who have requested coupons and notifications of sales in their local area.
> They currently have a dedicated customer base of around 5000 customers, but
> wish to grow this to 20,000 customers within the next 5 years. How much
> storage capacity will be required to store 20,000 customer records for the
> entire 5 year period, given the following information:
> First Name – 50 characters
> Last Name – 50 characters
> Address – 100 characters
> Suburb – 50 characters
> Phone number – 10 characters each (2 phone numbers per customer)
> Email address – 50 characters
> Postcode – 4 characters
> Number of coupons received – 32-bit number
>
>
>
> A. 34,200,000 bytes
>
> B. 32,400,000 bytes
>
> C. 35,600,000 bytes
>
> D. 32,800,000 bytes
>
>
>
> The solution gives D with the explanation
>
> 50+50+100+50+10+10+50+4+4 =
>
> 328
> 328 x 20000 x 5 = 32,800,000
>
> Why multiply by 5? Would the company recreate the entire records each
> year? I'd design it differently..
>
>
>
> Appreciate your help.
>
>
> Quentin Lydall
> Head of ICT
> Beaconhills College Valley Campus
> 30-34 Toomuc Valley Road,
> Pakenham
> 3810
> Phone: 1300 002 225 Extn 3016
>
> P Please consider the environment before printing my email
>
#####################################################################################
This email is confidential and intended solely for the use of the individual to whom
it is addressed. Any views or opinions presented are solely those of the author and
do not necessarily represent those of Beaconhills College. If you are not the
intended recipient, be advised that you have received this email in error and that
any use, dissemination, forwarding, printing, or copying of this email is strictly
prohibited.
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by telephone on (+61 3) 1300 002 225.
#####################################################################################
------------------------------
Message: 2
Date: Tue, 14 Oct 2008 12:51:48 +1100
From: Mark Kelly <kel at mckinnonsc.vic.edu.au>
Subject: Re: [Year 12 SofDev] Database question
To: "Year 12 Software Development Teachers' Mailing List"
<sofdev at edulists.com.au>
Message-ID: <48F3FB34.3010003 at mckinnonsc.vic.edu.au>
Content-Type: text/plain; charset=windows-1252; format=flowed
I see what you mean, but I think the question writer just used a
database as a vehicle for interrogating students' knowledge of number
types.
Since database structure is not part of the study design, a question
that required knowledge of indexes, normalisation, and relational links
etc could not, IMO, be justified.
2 cents worth (and devaluing rapidly). Only a year without teaching SD
and my memory of it is getting rusty already!
Cheers
Mark
Steven Bird wrote:
> On Tue, Oct 14, 2008 at 11:13 AM, Adrian Janson
> <janson.adrian.a at edumail.vic.gov.au> wrote:
>> Yes quite correct. My students spotted this as well. The x5 is not
>> required.
>
> There's some other problems though. A database with 20,000 customers
> should have one or more indexes to support efficient retrieval, and
> these take space. Nightly dumps take space as well. If the question
> is getting at how much disk space we should budget for, these factors
> are relevant.
>
> It would be bad database design to store postcode and suburb with each
> customer record (cf [1]). Instead a customer record should contain a
> foreign key to a table of postcodes, e.g. a subset of [2]. We're told
> the company only has sales in a "local area", so perhaps we'd only
> have to deal with a dozen postcodes. That table would be a constant
> size overhead which is easy to compute, and the foreign key would be a
> short integer (e.g. TINYINT).
>
> The question treats a database as if it was a spreadsheet, and only
> requires students to know the relative sizes of characters, bytes, and
> bits.
>
> It would be good if students learnt about normalization and the
> importance of avoiding duplication in a database. It would also be
> nice if they learnt what Unicode is, and that 1 character != 1 byte.
>
> [1] http://en.wikipedia.org/wiki/Database_normalization
> [2] http://www1.auspost.com.au/download/pc-full.zip
>
> -Steven Bird
> http://www.csse.unimelb.edu.au/~sb/
>
>> A database for an online marketing company keeps records of all customers
>> who have requested coupons and notifications of sales in their local area.
>> They currently have a dedicated customer base of around 5000 customers, but
>> wish to grow this to 20,000 customers within the next 5 years. How much
>> storage capacity will be required to store 20,000 customer records for the
>> entire 5 year period, given the following information:
>> First Name 50 characters
>> Last Name 50 characters
>> Address 100 characters
>> Suburb 50 characters
>> Phone number 10 characters each (2 phone numbers per customer)
>> Email address 50 characters
>> Postcode 4 characters
>> Number of coupons received 32-bit number
>>
>>
>>
>> A. 34,200,000 bytes
>>
>> B. 32,400,000 bytes
>>
>> C. 35,600,000 bytes
>>
>> D. 32,800,000 bytes
>>
>>
>>
>> The solution gives D with the explanation
>>
>> 50+50+100+50+10+10+50+4+4 =
>>
>> 328
>> 328 x 20000 x 5 = 32,800,000
>>
>> Why multiply by 5? Would the company recreate the entire records each
>> year? I'd design it differently..
>>
>>
>>
>> Appreciate your help.
>>
>>
>>
>>
>>
>> Quentin Lydall
>>
>> Head of ICT
>>
>> Beaconhills College Valley Campus
>>
>> 30-34 Toomuc Valley Road,
>>
>> Pakenham
>>
>> 3810
>>
>> Phone: 1300 002 225 Extn 3016
>>
>> P Please consider the environment before printing my email
>>
>>
>>
>> ________________________________
>>
>> This email is confidential and intended solely for the use of the
>> individual to whom it is addressed. Any views or opinions presented are
>> solely those of the author and do not necessarily represent those of
>> Beaconhills College. If you are not the intended recipient, be advised that
>> you have received this email in error and that any use, dissemination,
>> forwarding, printing, or copying of this email is strictly prohibited. If
>> you have received this email in error please notify Beaconhills College by
>> telephone on (+61 3) 1300 002 225.
>>
>> ________________________________
>>
>> _______________________________________________
>> http://www.edulists.com.au IT Software Development Mailing List kindly
>> supported by
>> http://www.vitta.org.au/vce/studies/infotech/softwaredevel3-4.html -
>> Victorian Curriculum and Assessment Authority and
>> http://www.vitta.org.au - VITTA Victorian Information Technology Teachers
>> Association Inc
>>
>> Important - This email and any attachments may be confidential. If received
>> in error, please contact us and delete all copies. Before opening or using
>> attachments check them for viruses and defects. Regardless of any loss,
>> damage or consequence, whether caused by the negligence of the sender or
>> not, resulting directly or indirectly from the use of any attached files our
>> liability is limited to resupplying any affected attachments. Any
>> representations or opinions expressed are those of the individual sender,
>> and not necessarily those of the Department of Education and Early Childhood
>> Development.
>>
>> _______________________________________________
>> http://www.edulists.com.au IT Software Development Mailing List kindly
>> supported by
>> http://www.vitta.org.au/vce/studies/infotech/softwaredevel3-4.html -
>> Victorian Curriculum and Assessment Authority and
>> http://www.vitta.org.au - VITTA Victorian Information Technology Teachers
>> Association Inc
>
> _______________________________________________
> http://www.edulists.com.au
> IT Software Development Mailing List kindly supported by
> http://www.vcaa.vic.edu.au - Victorian Curriculum and Assessment Authority and
> http://www.vitta.org.au/vce/studies/infotech/softwaredevel3-4.html - VITTA Victorian Information Technology Teachers Association Inc
>
>
>
--
Mark Kelly
Manager - Information Systems
McKinnon Secondary College
McKinnon Rd McKinnon 3204, Victoria, Australia
Direct line / Voicemail: 8520 9085
School Phone +613 8520 9000
School Fax +613 95789253
kel AT mckinnonsc.vic.edu.au
Webmaster - http://www.mckinnonsc.vic.edu.au
IT Lecture notes: http://vceit.com
Moderator: IT Applications Mailing List
A conclusion is the place where you got sick of thinking.
------------------------------
Message: 3
Date: Tue, 14 Oct 2008 11:58:39 +1100
From: "Kevork Krozian" <Kroset at novell1.fhc.vic.edu.au>
Subject: Re: [Year 12 SofDev] Special thanks to Associate Professor
Steven Bird
To: "Year 12 Software Development Teachers' Mailing List"
<sofdev at edulists.com.au>
Message-ID: <48F497EE.EE3E.0095.0 at novell1.fhc.vic.edu.au>
Content-Type: text/plain; charset=ISO-8859-15
Hi Steven,
I think we are very fortunate and privileged to have your time and
expertise on these lists.
I am sure you have other pressing demands on your time not least of
which in your lecturing and related duties in the Uni of Melbourne
Computer Science faculty and other projects, research and activities you
are working on as recorded on http://www.csse.unimelb.edu.au/~sb/ .
Your explanations and insights into implications of certain questions
on both the final and practice exams in Software Development can only
help us all to become better teachers if for no other reason than the
seed it plants to think about problems from another perspective and
hopefully continue the discussion and seek further clarification.
So on behalf of the list membership, please keep your comments coming
and thanks for your time.
Best Wishes
Kevork Krozian
IT Manager , Forest Hill College
k.krozian at fhc.vic.edu.au
http://www.fhc.vic.edu.au
Mobile: 0419 356 034
>>> "Steven Bird" <sb at csse.unimelb.edu.au> 14/10/2008 11:57 am >>>
On Tue, Oct 14, 2008 at 11:13 AM, Adrian Janson
<janson.adrian.a at edumail.vic.gov.au> wrote:
> Yes * quite correct. My students spotted this as well. The x5 is
not
> required.
There's some other problems though. A database with 20,000 customers
should have one or more indexes to support efficient retrieval, and
these take space. Nightly dumps take space as well. If the question
is getting at how much disk space we should budget for, these factors
are relevant.
It would be bad database design to store postcode and suburb with each
customer record (cf [1]). Instead a customer record should contain a
foreign key to a table of postcodes, e.g. a subset of [2]. We're told
the company only has sales in a "local area", so perhaps we'd only
have to deal with a dozen postcodes. That table would be a constant
size overhead which is easy to compute, and the foreign key would be a
short integer (e.g. TINYINT).
The question treats a database as if it was a spreadsheet, and only
requires students to know the relative sizes of characters, bytes, and
bits.
It would be good if students learnt about normalization and the
importance of avoiding duplication in a database. It would also be
nice if they learnt what Unicode is, and that 1 character != 1 byte.
[1] http://en.wikipedia.org/wiki/Database_normalization
[2] http://www1.auspost.com.au/download/pc-full.zip
-Steven Bird
http://www.csse.unimelb.edu.au/~sb/
> A database for an online marketing company keeps records of all
customers
> who have requested coupons and notifications of sales in their local
area.
> They currently have a dedicated customer base of around 5000
customers, but
> wish to grow this to 20,000 customers within the next 5 years. How
much
> storage capacity will be required to store 20,000 customer records
for the
> entire 5 year period, given the following information:
> First Name * 50 characters
> Last Name * 50 characters
> Address * 100 characters
> Suburb * 50 characters
> Phone number * 10 characters each (2 phone numbers per customer)
> Email address * 50 characters
> Postcode * 4 characters
> Number of coupons received * 32-bit number
>
>
>
> A. 34,200,000 bytes
>
> B. 32,400,000 bytes
>
> C. 35,600,000 bytes
>
> D. 32,800,000 bytes
>
>
>
> The solution gives D with the explanation
>
> 50+50+100+50+10+10+50+4+4 =
>
> 328
> 328 x 20000 x 5 = 32,800,000
>
> Why multiply by 5? Would the company recreate the entire records
each
> year? I'd design it differently..
>
>
>
> Appreciate your help.
>
>
>
>
>
> Quentin Lydall
>
> Head of ICT
>
> Beaconhills College Valley Campus
>
> 30-34 Toomuc Valley Road,
>
> Pakenham
>
> 3810
>
> Phone: 1300 002 225 Extn 3016
>
> P Please consider the environment before printing my email
>
>
>
> ________________________________
>
> This email is confidential and intended solely for the use of the
> individual to whom it is addressed. Any views or opinions presented
are
> solely those of the author and do not necessarily represent those of
> Beaconhills College. If you are not the intended recipient, be
advised that
> you have received this email in error and that any use,
dissemination,
> forwarding, printing, or copying of this email is strictly
prohibited. If
> you have received this email in error please notify Beaconhills
College by
> telephone on (+61 3) 1300 002 225.
>
> ________________________________
>
> _______________________________________________
> http://www.edulists.com.au IT Software Development Mailing List
kindly
> supported by
> http://www.vitta.org.au/vce/studies/infotech/softwaredevel3-4.html -
> Victorian Curriculum and Assessment Authority and
> http://www.vitta.org.au - VITTA Victorian Information Technology
Teachers
> Association Inc
>
> Important - This email and any attachments may be confidential. If
received
> in error, please contact us and delete all copies. Before opening or
using
> attachments check them for viruses and defects. Regardless of any
loss,
> damage or consequence, whether caused by the negligence of the sender
or
> not, resulting directly or indirectly from the use of any attached
files our
> liability is limited to resupplying any affected attachments. Any
> representations or opinions expressed are those of the individual
sender,
> and not necessarily those of the Department of Education and Early
Childhood
> Development.
>
> _______________________________________________
> http://www.edulists.com.au IT Software Development Mailing List
kindly
> supported by
> http://www.vitta.org.au/vce/studies/infotech/softwaredevel3-4.html -
> Victorian Curriculum and Assessment Authority and
> http://www.vitta.org.au - VITTA Victorian Information Technology
Teachers
> Association Inc
_______________________________________________
http://www.edulists.com.au
IT Software Development Mailing List kindly supported by
http://www.vcaa.vic.edu.au - Victorian Curriculum and Assessment
Authority and
http://www.vitta.org.au/vce/studies/infotech/softwaredevel3-4.html -
VITTA Victorian Information Technology Teachers Association Inc
------------------------------
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