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<p class=MsoPlainText>Hi everyone,<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>As the one writing the text book for 2011+, here is what
I have written for the definitions of array and record (there is more detail
and examples following these definitions):<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoNormal><b>One-Dimensional Arrays<o:p></o:p></b></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal style='text-align:justify'>A one dimensional (or 1D) array
is a data structure in which variables of the same type are grouped together
under the same name. <o:p></o:p></p>
<p class=MsoNormal style='text-align:justify'>...<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoNormal style='text-align:justify'><o:p> </o:p></p>
<p class=MsoNormal><b>Records<o:p></o:p></b></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span lang=EN-US>A record is a structure that can be used to
group together a variety of information for a particular purpose. Records
are similar to arrays but whereas an array has to contain elements all of the
same type, the variables within a record can be of different types.<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p>
<p class=MsoPlainText>...<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>I do think that there is a place for a standard definition
– as students will probably not use 1 language in their lives (assuming
that they progress to an IT course of some description), and even if they don’t,
the standard definition can set a context for a discussion of how the language
differs from this (if it is not strongly typed). I don’t think it
would hurt to say ‘the definition of an array is XYZ, however in PHP, an
array works in this way....’ Interesting to note that there are 6
languages for which the definitions above do not strictly hold! <o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>Is the concensus of this community that you would like me
to include more in these definitions about the distinction of strongly typed
languages? Or what is the general feeling about the definitions that I
have written above?<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>Cheers,<o:p></o:p></p>
<p class=MsoPlainText>Adrian<o:p></o:p></p>
<p class=MsoNormal><b><span style='font-size:18.0pt;font-family:"Times New Roman","serif";
color:#002060'><o:p> </o:p></span></b></p>
<p class=MsoNormal><b><span style='font-size:18.0pt;font-family:"Times New Roman","serif";
color:#002060'>Adrian Janson </span></b><b><span style='font-size:7.0pt;
font-family:"Times New Roman","serif";color:#002060'>B.Sc, Dip.Ed, M.Ed<br>
</span></b><b><span style='font-size:14.0pt;font-family:"Times New Roman","serif";
color:#002060'>Director of ICT<br>
</span></b><span style='font-size:12.0pt;font-family:"Times New Roman","serif";
color:#244061'>Melbourne High School, Forrest Hill, South Yarra, Victoria 3141
Australia.<br>
Phone: 03 9826 0711 International: +61 3 9826 0711<br>
Fax: 03 9826 8767 International: +61 3 9826 8767<br>
E-mail: <a href="janson.adrian.a@edumail.vic.gov.au"><span style='color:blue'>janson.adrian.a@edumail.vic.gov.au</span></a><o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:12.0pt;font-family:"Times New Roman","serif";
color:#244061'>Website: <a href="http://www.mhs.vic.edu.au/"><span
style='color:blue'>http://www.mhs.vic.edu.au</span></a></span><span
style='color:black'><o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:12.0pt;font-family:"Times New Roman","serif";
color:#244061'>Blog: <a href="http://jansona.edublogs.org/" target="_blank"><span
style='color:blue'>http://jansona.edublogs.org</span></a></span><span
style='color:black'><o:p></o:p></span></p>
<p class=MsoPlainText><span lang=EN-US>-----Original Message-----<br>
From: sofdev-bounces@edulists.com.au [mailto:sofdev-bounces@edulists.com.au] On
Behalf Of Laurie Savage<br>
Sent: Thursday, 19 August 2010 9:23 AM<br>
To: 'Year 12 Software Development Teachers' Mailing List'<br>
Subject: Re: [Year 12 SofDev] Records and Arrays</span><o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>Guy,<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>You are right, and of course I have taught this
distinction. As I mentioned<o:p></o:p></p>
<p class=MsoPlainText>to Maggie, I do object to teaching things that students
need to unlearn or<o:p></o:p></p>
<p class=MsoPlainText>that are irrelevant.<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>Laurie<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>-----Original Message-----<o:p></o:p></p>
<p class=MsoPlainText>From: sofdev-bounces@edulists.com.au
[mailto:sofdev-bounces@edulists.com.au]<o:p></o:p></p>
<p class=MsoPlainText>On Behalf Of Guy Flaherty<o:p></o:p></p>
<p class=MsoPlainText>Sent: Thursday, 19 August 2010 9:19 AM<o:p></o:p></p>
<p class=MsoPlainText>To: 'Year 12 Software Development Teachers' Mailing List'<o:p></o:p></p>
<p class=MsoPlainText>Subject: Re: [Year 12 SofDev] Records and Arrays<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>Laurie,<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>Typing is not really the issue, and Steven's explanation
is quite likely to<o:p></o:p></p>
<p class=MsoPlainText>cause more confusion in my opinion. Let me explain my
thinking:<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>The difference between a record and an array is simply
that one allows only<o:p></o:p></p>
<p class=MsoPlainText>one type of data to be used, the other allows multiple
types of data to be<o:p></o:p></p>
<p class=MsoPlainText>used (some languages require type to be declared, others
don't).<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>Associative 'arrays' are called 'arrays' in their
language literature, but<o:p></o:p></p>
<p class=MsoPlainText>according to the study design they are in fact 'records'
and not 'arrays'.<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>Java does not even have a record type, you have to create
a class with no<o:p></o:p></p>
<p class=MsoPlainText>instance methods to represent a 'record' type, so now you
have to include<o:p></o:p></p>
<p class=MsoPlainText>classes if you start thinking about Java. Additionally,
other languages,<o:p></o:p></p>
<p class=MsoPlainText>such as PHP, Python, Ruby etc can do the same thing as
Java but are not<o:p></o:p></p>
<p class=MsoPlainText>required to as their 'array' types can work as 'arrays'
or 'records'.<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>Ruby names their 'record' type an 'array' and their
'associative array' a<o:p></o:p></p>
<p class=MsoPlainText>'hash', making it even more difficult for students
learning Ruby to<o:p></o:p></p>
<p class=MsoPlainText>understand the Study Design definitions.<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>Thinking about all this, I am simply going to instruct my
students that for<o:p></o:p></p>
<p class=MsoPlainText>the purpose of completing any exam questions, the
difference between a<o:p></o:p></p>
<p class=MsoPlainText>record and an array IS that one can contain multiple
types of data and the<o:p></o:p></p>
<p class=MsoPlainText>other can only contain one type of data. Despite the fact
that this is not<o:p></o:p></p>
<p class=MsoPlainText>what they are seeing when they do their programming, this
is how it would<o:p></o:p></p>
<p class=MsoPlainText>seem to be best to approach it.<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>Guy Flaherty<o:p></o:p></p>
<p class=MsoPlainText> <o:p></o:p></p>
<p class=MsoPlainText>>>> "Laurie Savage"
<savage.john.l@edumail.vic.gov.au> 19/08/10 08:39 AM >>><o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>Well yes, and no. Thanks for the very clear description
of a record which IS<o:p></o:p></p>
<p class=MsoPlainText>an array (is ISBN an integer or a string? PHP will treat
it contextually)!<o:p></o:p></p>
<p class=MsoPlainText>However this does not take away from the fact that some
major modern<o:p></o:p></p>
<p class=MsoPlainText>languages are not strongly typed and so the study guide
distinction does not<o:p></o:p></p>
<p class=MsoPlainText>apply and this disadvantages students working in those
languages.<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText> <o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>Laurie<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText> <o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>From: sofdev-bounces@edulists.com.au [mailto:sofdev-bounces@edulists.com.au]<o:p></o:p></p>
<p class=MsoPlainText>On Behalf Of Steven Bird<o:p></o:p></p>
<p class=MsoPlainText>Sent: Wednesday, 18 August 2010 8:58 PM<o:p></o:p></p>
<p class=MsoPlainText>To: Year 12 Software Development Teachers' Mailing List<o:p></o:p></p>
<p class=MsoPlainText>Subject: Re: [Year 12 SofDev] Records and Arrays<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText> <o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>The following might help you to distinguish these
concepts.<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>Consider any kind of real world entity, e.g. a student, a
school, a book, a<o:p></o:p></p>
<p class=MsoPlainText>patient, etc. Now think about its attributes.
For a book this might be<o:p></o:p></p>
<p class=MsoPlainText>title, author, year, isbn, price... When we model
such an entity using a<o:p></o:p></p>
<p class=MsoPlainText>computer, we specify a set of attributes. This is a
"record". It is just a<o:p></o:p></p>
<p class=MsoPlainText>collection of attributes describing an entity.<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>A record could be stored on disk (e.g. as a row of a
relational database<o:p></o:p></p>
<p class=MsoPlainText>table, or as a row of a CSV file), or represented in
volatile memory in a<o:p></o:p></p>
<p class=MsoPlainText>data structure in a running program. Perhaps the
most common data type used<o:p></o:p></p>
<p class=MsoPlainText>for representing a record is an "associative
array" ("hash" in Perl;<o:p></o:p></p>
<p class=MsoPlainText>"dictionary" in Python; "array" (!)
in PHP, "map" in C++); some languages<o:p></o:p></p>
<p class=MsoPlainText>support a "tuple" type which is also
appropriate for representing records.<o:p></o:p></p>
<p class=MsoPlainText>However, at one level these details don't matter.
What's important is just<o:p></o:p></p>
<p class=MsoPlainText>that we have a set of attributes.<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>Now consider any collection of entities of the same type,
e.g. students,<o:p></o:p></p>
<p class=MsoPlainText>schools, books, patients, etc. When we model these
in a computer, we<o:p></o:p></p>
<p class=MsoPlainText>specify a collection of like entities. This is just
a set or list of<o:p></o:p></p>
<p class=MsoPlainText>entities.<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>This list could be stored on disk (e.g. as a relational
table, or a CSV<o:p></o:p></p>
<p class=MsoPlainText>file), or represented in a running program. The most
common data type is an<o:p></o:p></p>
<p class=MsoPlainText>"array", and that's what it is called in most
languages (but it is "list" in<o:p></o:p></p>
<p class=MsoPlainText>Python). Some languages encourage you to define
array elements to be all of<o:p></o:p></p>
<p class=MsoPlainText>the same type, but not all. In general, I think
this is a good practice.<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>PHP blurs the distinction between records and
arrays. However, a programmer<o:p></o:p></p>
<p class=MsoPlainText>can use PHP in such a way to keep them quite distinct:<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>my_record1 = array('isbn'=>1441412050,
'title'=>'Alice in Wonderland',<o:p></o:p></p>
<p class=MsoPlainText>'author'=>'Lewis Carroll');<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>my_record2 = array('isbn'=>1441412050,
'title'=>'Through the Looking Glass',<o:p></o:p></p>
<p class=MsoPlainText>'author'=>'Lewis Carroll');<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>my_array = array(my_record1, my_record2);<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>my_record1['isbn']; /* access a record's
attribute by name */ <o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>my_array[1];
/* access an array's element by index */<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>I hope this helps!<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>--<o:p></o:p></p>
<p class=MsoPlainText>Steven Bird<o:p></o:p></p>
<p class=MsoPlainText>http://stevenbird.me/<o:p></o:p></p>
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<p class=MsoPlainText>Date: 2010-08-19 08:45:37.693<o:p></o:p></p>
<p class=MsoPlainText>From: sofdev-bounces@edulists.com.au<o:p></o:p></p>
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