[Year 12 SofDev] Records and Arrays

Thu Aug 19 18:42:46 EST 2010

Hello all

Don I think you touch on the most important point: the concept is the thing, 
not how it is implemented (or not) in any given language.

So, (to meet the requirements of 'old' and 'new' languages) an array is a 
named collection of elements which
may or may not be of the same type, and which are all individually accessed 
via a numerical index or indices.

As for a 'record', if we are talking about named data structures that exist 
(normally in memory) at program run time, then I agree it is an unfortunate 
term in that context but only because we are so used to thinking of records 
as part of a file on disk. I also agree that Pascal is probably the only 
language to use the term in reference to a 'memory structure', but in the 
context of Pascal it makes perfect sense, and, as Steven points out, 
conceptually there isn't any difference. As I said, I think we have it so 
ingrained in us to think of it as part of a file. Also creating further 
confusion is the the term 'associative array' which looks an awful lot like 
what Pascal calls a record, but throws in the word 'array'. (Although I 
suspect that an associative array is in fact a broader generalisation that 
encompassed both 'traditional arrays' and 'records').

So, a record (memory structure or not) is a named collection of elements 
which may or may not be of the same type, and which are individually 
accessed by, as Steven also points out, by an 'attribute name'. Also, a 
record is 'one-dimensional' (Although you could have an array of records in 
which case Pascal would say you have a file!)

Regards
Robert T-A
Brighton SC

----- Original Message ----- 
From: "Don Morelli (Optus)" <da_morelli at optusnet.com.au>
To: "'Year 12 Software Development Teachers' Mailing List'" 
<sofdev at edulists.com.au>
Sent: Thursday, August 19, 2010 4:45 PM
Subject: Re: [Year 12 SofDev] Records and Arrays

> This discussion is fantastic and I understand and agree with many of the
> issues raised. However, it again highlights the need for a set of
> definitions that we all adhere to, no matter what our practical 
> experience.
> This type of discussion has been raised many times over different
> definitions. As teachers, we need to know what is the definition according
> to the assessing body and the people who are setting the exam, so that all
> students can have the same opportunity at getting exam questions correct 
> no
> matter who the teacher is. I know that it would not happen, but I would be
> appalled if definitions changed as a result of discussion on this list or
> any other list, as these are subscribed to on an interest basis. It would
> disadvantage other teachers who are not members of the list (and their
> students).
> We need to remember that it is the algorithm and knowledge that we are
> teaching and will be tested, and not how it is implemented in a particular
> language.
> Adrian's definition is fine and in my opinion does not need to be changed,
> as it clearly distinguishes between two different types of data 
> structures.
> Particularly if this is what the examiners are looking for in their
> definition of records and arrays. We are possibly using Python next year 
> as
> we used good old VB6, but I will deal with the practical side of
> implementing these data structures and still teach the "old definitions".
> Anyway thanks for the discussion as it makes the job of teaching much more
> interesting.
> Cheers Don
>
> -----Original Message-----
> From: sofdev-bounces at edulists.com.au 
> [mailto:sofdev-bounces at edulists.com.au]
> On Behalf Of Guy Flaherty
> Sent: Thursday, 19 August 2010 11:48 AM
> To: 'Year 12 Software Development Teachers' Mailing List'
> Subject: Re: [Year 12 SofDev] Records and Arrays
>
> Laurie,
>
> I only mentioned it as Adrian had talked about it and I feel it is 
> important
> but not part of the ARRAY / RECORD discussion. Wasn't trying to belabor a
> point ;)
>
> As for RECORD, I think any definition needs to very clearly differentiate
> between the 'common' use of the term and the SD use of the term, as they 
> are
> quite different. The SD definition is the 'base' functionality that the 
> type
> provides, allowing for data of different types to be stored as a group 
> that
> can be referenced using a single pointer. The common use is how we, as
> humans, have come to use such a structure, but it in no way is required 
> that
> the 'RECORD' type be used in such a way. To give a very poor analogy, a
> hammer is usually used for hitting nails and is probably how most people
> would think of one if they had to describe it, but it is not required to 
> hit
> nails and can be used for other things as well. The problem with trying to
> teach what a 'record' is comes when you start to confuse the common use,
> such as for database rows and fields, and what it actually is according to
> the SD definition, a simple data structure.
>
> The more I think about it the more I feel the current definitions are 
> simple
> to understand and explain the differences the best. The trouble is they 
> are
> not accurately reflecting what many students will be seeing as they learn
> about programming languages. I agree with John, in that if we have to have
> them keep them as they are. To answer Adrian's question, I simply feel he
> needs to include something that explains how these definitions may not 
> apply
> in real world applications. I will have to make a point of explaining to 
> my
> students that even though the vast majority of literature states something
> is an array (depending on the language you are using), in SD terms it is a
> record! Makes sense, right?!
>
> Guy Flaherty
>
> PS. Sorry Adrian, I just got your latest message now :D
>
>>>> "Laurie Savage" <savage.john.l at edumail.vic.gov.au> 19/08/10 11:10 AM 
>>>>  >>>
>
> Guy,
>
> I realised I had misused "typing" after sending the messages. I was using 
> it
> as shorthand for what we were discussing, which was pretty dumb of me.
> Thanks for the extensive coverage of real world usages. I think the 
> concept
> of a RECORD has a use in the pencil and paper stages but that is very
> different from the SD definition.
>
> Laurie
>
> -----Original Message-----
> From: sofdev-bounces at edulists.com.au 
> [mailto:sofdev-bounces at edulists.com.au]
> On Behalf Of Guy Flaherty
> Sent: Thursday, 19 August 2010 10:51 AM
> To: 'Year 12 Software Development Teachers' Mailing List'
> Subject: Re: [Year 12 SofDev] Records and Arrays
>
> Adrian,
>
> An interesting question you are asking there! If you are looking for a
> 'standard' definition, I am unsure how you can provide one when half of 
> the
> approved languages work one way and the other half work in a different 
> way.
> If your definition is based on common usage you would likely have to
> conclude that there is no 'record' type in real world usage as it is
> currently defined, as only Pascal appears to use this structure and names 
> it
> as a 'record'. Other languages have similar structures but do not call 
> them
> 'records', and other languages treat everything as a 'record' according to
> this definition and can also use the same structure as an array. In 
> current
> usage, an 'array' can only be defined relative to any one particular
> language, as what an array can actually do depends on the language.
>
> If I were a student and I saw a definition for an array that stated that
> everything I had learned about programming 'arrays' in the language I was
> using was not correct, well, I think I would quickly become confused.
>
> If you look at it in terms of language popularity:
>
> 1. Java -  has array but no record like type (must use a class, so not 
> very
> helpful)
> 2. C - has array but doesn't have 'record' as such, as it is named as
> 'struct' but fulfills the same purpose
> 3. C++ - same as C
> 4. PHP - Has only 'record' type but known only as 'array'. Can be used as
> both an 'array' or as a 'record'
> In no order (roughly similar real world usage)
>    C# - very similar to C
>    VB - very similar to C#
>    Python - has 'list', 'tuple', & 'dictionary' but all commonly referred
> to as 'arrays' when they are in fact either depending on use, according to
> SD definition
>    Perl - very similar to PHP
>    Objective C - Allows for some use of C 'structs' but names them as
> 'arrays' when in fact it would be defined as a 'record' in SD (Can be used
> as an 'array')
>    Ruby - very similar to PHP
> 11. Pascal - Follows the SD definitions fully, and is probably where they
> originated as it is the oldest of the languages
> Not even used??? Visual Fox Pro - similar to PHP
>
> So, merging that down into a simple definition, such as we are using in 
> the
> current study design, of ARRAY and RECORD would seem rather pointless for
> the 'newer' languages and completely appropriate for the more 
> 'established'
> languages.
>
> To me, RECORD seems totally irrelevant, as it is only ever named that in
> Pascal and no other language refers to their type as a 'Record'. An ARRAY
> can only be defined relevant to the language you are using, and this is 
> how
> I think you should explain it in your book, for real world usage. If the 
> new
> study design insists that we continue with the current definitions then 
> that
> should be the main explanation given, with an aside about real world usage
> and language difference. That would seem to be very relevant for students 
> in
> my opinion.
>
> Finally, typing has no relevance in the definitions. It does not matter if 
> a
> language uses static or dynamic typing when comparing the current
> definitions of ARRAY and RECORD. If you start talking about typing then I
> believe you are just going to confuse students even more by including a
> totally separate issue.
>
> Guy Flaherty
>
>>>> "Adrian Janson" <janson.adrian.a at edumail.vic.gov.au> 19/08/10 10:01 AM
>>>>
> Hi everyone,
>
>
>
> 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):
>
>
>
>
>
> One-Dimensional Arrays
>
>
>
> A one dimensional (or 1D) array is a data structure in which variables of
> the same type are grouped together under the same name.
>
> ...
>
>
>
>
>
> Records
>
>
>
>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.
>
>
>
> ...
>
>
>
> 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!
>
>
>
> 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?
>
>
>
> Cheers,
>
> Adrian
>
>
>
> Adrian Janson B.Sc, Dip.Ed, M.Ed
> Director of ICT
> Melbourne High School, Forrest Hill, South Yarra, Victoria 3141 Australia.
> Phone: 03 9826 0711 International: +61 3 9826 0711
> Fax: 03 9826 8767 International: +61 3 9826 8767
> E-mail: janson.adrian.a at edumail.vic.gov.au
>
> Website:  <http://www.mhs.vic.edu.au/> http://www.mhs.vic.edu.au
>
> Blog:  <http://jansona.edublogs.org/> http://jansona.edublogs.org
>
> -----Original Message-----
> From: sofdev-bounces at edulists.com.au 
> [mailto:sofdev-bounces at edulists.com.au]
> On Behalf Of Laurie Savage
> Sent: Thursday, 19 August 2010 9:23 AM
> To: 'Year 12 Software Development Teachers' Mailing List'
> Subject: Re: [Year 12 SofDev] Records and Arrays
>
>
>
> Guy,
>
>
>
> You are right, and of course I have taught this distinction. As I 
> mentioned
>
> to Maggie, I do object to teaching things that students need to unlearn or
>
> that are irrelevant.
>
>
>
> Laurie
>
>
>
> -----Original Message-----
>
> From: sofdev-bounces at edulists.com.au 
> [mailto:sofdev-bounces at edulists.com.au]
>
> On Behalf Of Guy Flaherty
>
> Sent: Thursday, 19 August 2010 9:19 AM
>
> To: 'Year 12 Software Development Teachers' Mailing List'
>
> Subject: Re: [Year 12 SofDev] Records and Arrays
>
>
>
> Laurie,
>
>
>
> Typing is not really the issue, and Steven's explanation is quite likely 
> to
>
> cause more confusion in my opinion. Let me explain my thinking:
>
>
>
> The difference between a record and an array is simply that one allows 
> only
>
> one type of data to be used, the other allows multiple types of data to be
>
> used (some languages require type to be declared, others don't).
>
>
>
> Associative 'arrays' are called 'arrays' in their language literature, but
>
> according to the study design they are in fact 'records' and not 'arrays'.
>
>
>
> Java does not even have a record type, you have to create a class with no
>
> instance methods to represent a 'record' type, so now you have to include
>
> classes if you start thinking about Java. Additionally, other languages,
>
> such as PHP, Python, Ruby etc can do the same thing as Java but are not
>
> required to as their 'array' types can work as 'arrays' or 'records'.
>
>
>
> Ruby names their 'record' type an 'array' and their 'associative array' a
>
> 'hash', making it even more difficult for students learning Ruby to
>
> understand the Study Design definitions.
>
>
>
> Thinking about all this, I am simply going to instruct my students that 
> for
>
> the purpose of completing any exam questions, the difference between a
>
> record and an array IS that one can contain multiple types of data and the
>
> other can only contain one type of data. Despite the fact that this is not
>
> what they are seeing when they do their programming, this is how it would
>
> seem to be best to approach it.
>
>
>
> Guy Flaherty
>
>
>
>>>> "Laurie Savage" <savage.john.l at edumail.vic.gov.au> 19/08/10 08:39 AM 
>>>>  >>>
>
>
>
> Well yes, and no. Thanks for the very clear description of a record which 
> IS
>
> an array (is ISBN an integer or a string? PHP will treat it contextually)!
>
> However this does not take away from the fact that some major modern
>
> languages are not strongly typed and so the study guide distinction does 
> not
>
> apply and this disadvantages students working in those languages.
>
>
>
>
>
>
>
> Laurie
>
>
>
>
>
>
>
> From: sofdev-bounces at edulists.com.au 
> [mailto:sofdev-bounces at edulists.com.au]
>
> On Behalf Of Steven Bird
>
> Sent: Wednesday, 18 August 2010 8:58 PM
>
> To: Year 12 Software Development Teachers' Mailing List
>
> Subject: Re: [Year 12 SofDev] Records and Arrays
>
>
>
>
>
>
>
> The following might help you to distinguish these concepts.
>
>
>
> Consider any kind of real world entity, e.g. a student, a school, a book, 
> a
>
> patient, etc.  Now think about its attributes.  For a book this might be
>
> title, author, year, isbn, price...  When we model such an entity using a
>
> computer, we specify a set of attributes.  This is a "record".  It is just 
> a
>
> collection of attributes describing an entity.
>
>
>
> A record could be stored on disk (e.g. as a row of a relational database
>
> table, or as a row of a CSV file), or represented in volatile memory in a
>
> data structure in a running program.  Perhaps the most common data type 
> used
>
> for representing a record is an "associative array" ("hash" in Perl;
>
> "dictionary" in Python; "array" (!) in PHP, "map" in C++); some languages
>
> support a "tuple" type which is also appropriate for representing records.
>
> However, at one level these details don't matter.  What's important is 
> just
>
> that we have a set of attributes.
>
>
>
> Now consider any collection of entities of the same type, e.g. students,
>
> schools, books, patients, etc.  When we model these in a computer, we
>
> specify a collection of like entities.  This is just a set or list of
>
> entities.
>
>
>
> This list could be stored on disk (e.g. as a relational table, or a CSV
>
> file), or represented in a running program.  The most common data type is 
> an
>
> "array", and that's what it is called in most languages (but it is "list" 
> in
>
> Python).  Some languages encourage you to define array elements to be all 
> of
>
> the same type, but not all.  In general, I think this is a good practice.
>
>
>
> PHP blurs the distinction between records and arrays.  However, a 
> programmer
>
> can use PHP in such a way to keep them quite distinct:
>
>
>
> my_record1 = array('isbn'=>1441412050, 'title'=>'Alice in Wonderland',
>
> 'author'=>'Lewis Carroll');
>
>
>
>
>
>
>
>
>
>
>
>
>
> my_record2 = array('isbn'=>1441412050, 'title'=>'Through the Looking 
> Glass',
>
> 'author'=>'Lewis Carroll');
>
>
>
>
>
>
>
>
>
>
>
> my_array = array(my_record1, my_record2);
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> my_record1['isbn'];   /* access a record's attribute by name */
>
>
>
>
>
> my_array[1];          /* access an array's element by index */
>
>
>
> I hope this helps!
>
>
>
> --
>
> Steven Bird
>
> http://stevenbird.me/
>
>
>
>
>
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> Date: 2010-08-19 08:45:37.693
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