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semantic level of SVG usage

From: Rich Morin <rdm@cfcl.com>
Date: Wed, 17 Aug 2016 09:20:52 -0700
Cc: www-svg <www-svg@w3.org>
Message-Id: <EB6655F1-9268-41B7-B96E-3889A9B5E2DC@cfcl.com>
To: "w3c-wai-ig@w3.org" <w3c-wai-ig@w3.org>
Although I like the idea of adding ARIA metadata to SVG, I'm concerned
that its effectiveness may be extremely limited by the semantic level
of SVG tags and their typical usage.

# Motivation

Consider a data flow diagram, as produced by OmniGraffle. The building
blocks of the diagram are geometric shapes and arrows, but this level
of abstraction is largely absent from the SVG.  Instead, it uses either
a filled `path` or a pair of `rect` elements.

And, although the semantic payload of the diagram is largely concerned
with connectivity, the SVG contains no information on this.  The only
way I can see to get connectivity information is to compare locations
of line endpoints with the (fuzzy) boundaries of geometric shapes.

I have similar concerns about other kinds of plots and diagrams.  For
example, the semantic payload of a pie chart or a histogram has to do
with the numeric quantities being represented, not with the angles or
heights used in the generated image.

The SVG images produced by D3.js are even more problematic, using tags
which have only a distant relationship to the semantic payload:

  https://github.com/d3/d3/wiki/gallery
  http://bl.ocks.org/mbostock

In summary, adding attributes to SVG tags may not be enough to make
the resulting image particularly accessible.

# Proposal

By combining SVG attributes (e.g., object identity) with a separate
section of the XML document, it would be possible to add arbitrary
semantic information to the image.  For example, the added section
could describe graph connectivity, encode raw data for plots, etc.

This could support a variety of post-processing needs, ranging from
accessibility to machine learning.  And, because the added section
wouldn't be part of the base SVG, programs could simply ignore it.

Comments and suggestions welcome.

-r

P.S.  Amanda Lacy, Johannes Rössel, and Gene Dronek contributed
      valuable information and insights to this note, but they
      are not responsible for my conclusions.

-- 
http://www.cfcl.com/rdm           Rich Morin           rdm@cfcl.com
http://www.cfcl.com/rdm/resume    San Bruno, CA, USA   +1 650-873-7841

Software system design, development, and documentation
Received on Wednesday, 17 August 2016 16:21:25 UTC

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