[MEI-L] Repeats

Andrew Hankinson andrew.hankinson at mail.mcgill.ca
Tue Jul 19 03:16:22 CEST 2016


Thanks Craig! I remember that e-mail now, but I think there is still an issue with the confusion and mixing of domains. The signs in the notation ("visual") and the order it is performed ("gestural") should probably be encoded separately from the the structural indications of a repeated section ("logical"). It is currently impossible, for example, to use the attributes to encode an invisible repeat barline (or an invisible double barline, for that matter). 

Of course, it may be that invisible repeats are silly things, but I think the fact that you can control both functionality and appearance in a single attribute is probably an indication that it needs to be re-worked.

-Andrew

> On Jul 18, 2016, at 9:02 PM, Craig Sapp <craigsapp at gmail.com> wrote:
> 
> Hi Andrew,
> 
> Here is an email from Perry to this list on 16 June 2015 related to the subject:
> 
> -=+Craig
> 
> =====
> 
> I thought this was covered in the Guidelines, but taking a closer look, I find that it isn't.  So, I'll try to explain.
> 
> There are multiple aspects of repeated sections that must be taken into account.  First, there are the signs found in the notation. Second, there is the question of how the signs should be interpreted in performance.  The first aspect is partially covered, as you already know, by the @left and @right attributes on <measure>.  The second is encoded using the <expansion> element.  <expansion> provides the means to encode the performance order of <section> and <ending> elements.  There could be multiple interpretations of the repeat structure, so <expansion> is repeatable.
> 
> Here's an encoding of the relevant portion of your first example:
> 
> <section>
>   <expansion plist="A Ending1 A Ending1 A Ending2"/>
>   <section xml:id="A">
>     <measure n="1" left="rptstart"/>
>     <!-- measures 2 - 8 -->
>   </section>
>   <ending n="1" xml:id="Ending1" label="1. 2.">
>     <measure n="9" right="rptend"/>
>   </ending>
>   <ending n="2" xml:id="Ending2" label="3.>
>     <measure n="10" right="end"/>
>   </ending>
> </section>
> 
> The repeat signs and the ending bar are encoded using @left and @right attributes.  <ending> elements are used to wrap the measures under the first and second ending brackets.  In order to be able to assign an ID to the repeated part of the music (measures 1 - 8), these measures are wrapped in a child <section> element.  It's the performance order of the children of this outer section that the <expansion> element's @plist attribute describes: section A, then Ending1, section A, then Ending1, section A, then Ending2.  
> 
> The only other "wrinkle" is the labeling of the endings.  The @n attribute can be used to give a number or name to elements, such as the endings in this case.  But, since @n can only hold a single token, if you want a space in the name, it's better to use the @label attribute. (I'll leave the larger discussion of "name" vs. "label" for another time.)
> 
> Your second example doesn't introduce any new problems, so I leave it to you to work out its encoding.  If you run into difficulty, though, just let me know.
> 
> 
> On 18 July 2016 at 17:56, Andrew Hankinson <andrew.hankinson at gmail.com <mailto:andrew.hankinson at gmail.com>> wrote:
> Hi everyone,
> 
> I was just looking at how repeats are defined, and it strikes me as a bit odd.
> 
> Currently, it seems as though repeats are encoded by using the `@right` and `@left` attributes on `<measure>`. My biggest concern with this is that it seems to confuse logical and visual functions of repeats; that is, it encodes where a particular symbol is drawn, but doesn't actually encode the semantic existence of a repeat.
> 
> I am also trying to figure out the note on `@left` which, essentially, states that you should not use it. I'm not sure how else you would encode a repeat start on a measure without using `@left="rptstart"`. Any insights?
> 
> An alternate solution may be to re-work '@left' and '@right' into three new attributes to separate visual from functional. The first `@repeat`, takes values of "start", "end", or "both." Two others, "@startbarline" and "@endbarline" can contain the visual values "dbldotted", "dbldashed", etc. A Schematron rule might be set up to catch the cases where there exists 'repeat="start"' and 'startbarline="dbldotted"' and set a warning or an error. (It may be desirable to have 'repeat="start"' and 'startbarline="invis"', though...)
> 
> -Andrew
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