W3C home > Mailing lists > Public > public-openannotation@w3.org > May 2013

minor whine about documentation arrows

From: Bob Morris <morris.bob@gmail.com>
Date: Fri, 24 May 2013 17:26:39 -0400
Message-ID: <CADUi7O6wShSGBswKc3dCQs5mpMjX+Karx3Tesfe6N0-a5dEjuQ@mail.gmail.com>
To: public-openannotation <public-openannotation@w3.org>
OK, I understand that the graphical conventions [1] in the Feb 2013
spec are purely informative, and about the doc, not the model. But I
have come to decide that in publications it would be helpful to stay
as close to the graphics of the spec doc as feasible. In attempting to
do so, I have---so far-- one minor whine and one whimper.

Whine: I see no powerful reason to distinguish object predicates'
arrows from datatype predicates' arrows by whether they are straight
or curved.  That distinction should be guided by the layout
constraints in the diagram.  For both cases, it is easy to find
oneself forced into graphical ugliness by sticking to the convention.
Among the consequences are wasteful extra white space needed when
straight arrows are "required" and silly trivial curves when curved
ones are "required".  By "required" I only mean, "attempting to follow
the documentation conventions." Besides all that, the two types are
already distinguished by the shape of their targets---ellipses for
objects, lozenges for literals. So it would be nice if the
documentation were simply silent on the matter of curves or straight
arrows.  It wouldn't even require changing the pictures.

Whimper:  It's a stretch to say "Class instantiation (rdf:type) is
depicted as a straight black line with white arrow head, following
UML."  Most (all?) UML systems produce diagrams in which the
equivalent of rdf:type is denoted with ":" in the label of a box
depicting the object and its properties.  There are no arrows for this
particular UML association between instances and classes. Other
associations between any UML objects are denoted with solid lines,
and, if those associations are directional, with open arrowheads.
Open arrows are generally (always?) reserved for the "generalizes"
association, useful in specifying a class hierarchy.  I like the
triangular headed arrow convention for rdf:type, because it's an easy
to find graphical signpost that let's you ignore the predicate name
when it doesn't matter. But crediting it to UML makes me more, not
less, confused, especially in the face of other UML reserved words,
like "association" that are also used differently in UML.   I would
remove "following UML" from  [1].

Bob Morris

[1] http://www.openannotation.org/spec/core/index.html#Examples
Robert A. Morris

Emeritus Professor  of Computer Science
100 Morrissey Blvd
Boston, MA 02125-3390

IT Staff
Filtered Push Project
Harvard University Herbaria
Harvard University

email: morris.bob@gmail.com
web: http://efg.cs.umb.edu/
web: http://wiki.filteredpush.org
The content of this communication is made entirely on my
own behalf and in no way should be deemed to express
official positions of The University of Massachusetts at Boston or
Harvard University.
Received on Friday, 24 May 2013 21:27:14 UTC

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