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Volume 21 (2002), number 4 pp. 777–786 COMPUTER GRAPHICS forum
SVG Linearization and Accessibility
Ivan Herman1 and Daniel Dardailler2
1World Wide Web Consortium, c/o W3C Benelux Office at CWI, 1098 SJ Amsterdam, The Netherlands
2World Wide Web Consortium, c/o INRIA, 2004, route de Lucioles, B.P. 93, 06902 Sophia Antipolis Cedex, France
ivan@w3.org, danield@w3.org
Abstract
The usage of SVG (Scaleable Vector Graphics) creates new possibilities as well as new challenges for the
accessibility of Web sites. This paper presents a metadata vocabulary to describe the information content of
an SVG file geared towards accessibility. When used with a suitable tool, this metadata description can help
in generating a textual (“linear”) version of the content, which can be used for users with disabilities or with
non-visual devices.
Although this paper concentrates on SVG, i.e. on graphics on the Web, the metadata approach and vocabulary
presented below can be applied in relation to other technologies, too. Indeed, accessibility issues have a much
wider significance, and have an effect on areas like CAD, cartography, or information visualization. Hence, the
experiences of the work presented below may also be useful for practitioners in other areas.
Keywords: 2D graphics, Scalable Vector Graphics (SVG), web accessibility, metadata in graphics, semantic web
ACM CSS: I.3.4 Graphics Utilities—Graphics Packages, I.3.6 Methodology and Techniques—Graphics data
structures and data types, Standards, K.4.2 Social Issues—Assistive technologies for persons with disabilities
1. Introduction
Images play an important role in conveying information on
the Web. However, the information presented in images must
be accessible to all users, including those with visual dis-
abilities or simply using non-visual devices. This problems
has been recognized for a while already. For example, the
Web Content Accessibility Guidelines [19], published by the
World Wide Web Consortium (W3C), addresses this issue as
part of its checklist. With reference to graphics, for example,
authors of Web pages using traditional HTML are supposed
to make use of the extra attributes available in the img ele-
ment (alt, longdesc): using these attributes, the author
can give a textual equivalent of the information contained in
the image. Based on these attributes a specialized browser is
able to convey the right information to the user (in parallel
to or instead of the graphics content itself).
In this respect, SVG [4,17] creates new possibilities as
well as new challenges. Some elements of SVG, namely the
title and desc elements, make it possible to annotate
every element in an SVG file. Thus, extra information can
be provided, by-passed by a “traditional” viewer but usable
by specialized user agents. This, and other accessibility
features of SVG (grouping, styling, etc.) have already been
explored by McCathieNevile and Koivunen in a W3C Note
[8]. However, their approach is by no means a complete
solution to the problem.
SVG is also very different from a traditional PNG or JPEG
image. A bitmap image does not reveal the original structure
of the information content. For example, the fact that one
object in the image is “behind” or “on the left” of another
cannot be retrieved from the pixels themselves (except
maybe through sophisticated image analysis); unless the
accompanying description is very verbose, it is quite difficult
to add this sort of information to description attribute values.
On the other hand, the SVG file itself retains these sorts
of relationships and they are potentially available on the
client side. This means that the information, which can be
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conveyed to a user with disabilities (or using non-visual
devices) can be potentially much richer and more complex,
hence also much more informative. Also, SVG may include
animation and interaction; revealing the dynamic aspect of
the SVG content may be essential to understand the content
of the graphics.
A more systematic usage of metadata is a possible step
forward. The term metadata (or “data about data”) has
been used for a while to denote data describing a particular
resource (whether on the Web or not). A typical example
is the cataloguing system used by libraries. The electronic
version of metadata, often included in the resource itself,
has come to the fore with the appearance of digital libraries,
on-line databases, etc. These applications often rely on the
availability of a coherent metadata about their resources,
using a well-established, common vocabulary.
The World Wide Web consortium has engaged into an
activity called the “Semantic Web” [2] whose goal is
to provide a systematic, and standardized mechanism to
define and describe metadata for Web resources. As part
of this activity, W3C has defined the Resource Description
Framework (RDF) [13,14], which is a way to encode
simple metadata statements in XML. Furthermore, the
metadata element in SVG allows the inclusion of any
XML vocabulary into the SVG file; this data is ignored
by the usual graphics players, but can be used by other
processing agents. For example, through the inclusion of
RDF into the metadata it is possible to add additional,
and more structured information on the SVG content. Using
RDF has the extra advantage of using a standardized
formalism for metadata, thereby being able to re-use tools,
visual editors, etc., to generate and process the metadata
itself. (If the user is not familiar with RDF and/or its
representation in XML, the RDF Primer can be particularly
useful [14].)
The idea of the linealizer tool, described in this paper, is
to extract information from the SVG file using the included
metadata and to produce a textual (“linear”) description of
the information content of the graphics. This description,
in our case a simple and text-only HTML file, can be used,
for example, by a voice browser. This linealizer tool is
not simply a metadata to HTML converter, though; while
interpreting the metadata elements, the tool also extracts
further information from the SVG structure itself. This
approach has been first explored by Lovet and Dardailler in
their SVG linearizer tool [6], as part of Lovet’s internship
at W3C/INRIA. This report continues the work explored by
Lovet and Dardailler, by revisiting, improving, and extend-
ing the metadata vocabulary used in the original report and
by extending the functionality of the linealizer tool.
In short, the tool performs the following steps:
(1) The author describes the SVG content using an RDF
vocabulary described below. In general, this RDF
information can be either embedded into the SVG file
or can be in a separate file.
(2) The author also adds textual descriptions using the
desc elements to (at least!) all elements which
are referred to as primary RDF resources. All these
elements should also be identifiable through an id
attribute. For a specific element the tools considers the
first child desc element as being the corresponding
description.
(3) The linealizer tool reads the RDF information, com-
bines each RDF resource with the textual description,
possibly extract further information from the SVG file
itself, and produces a simple HTML file on its output.
The rest of this paper concentrates on the RDF vocabulary
used. The tool can be downloaded and tested; more about
that below.
2. Some examples
The tool has been tested on a number of SVG files. All the
files, as well as the generated HTML files, are available on-
line, using the base URL:
http://www.svgopen.org/papers/2002/
herman_dardailler_svg__linearization_
and_accessibility/
The first example has also been reproduced in the Appendix.
The detailed description of the predicates in this paper makes
use of the metadata contained in these files.
3. Predicates
This section gives a definition of the RDF predicates.
By default, the linealizer tool displays a textual version
of the predicate, including some simple structure (e.g. in the
form of bulleted lists) when possible. In some cases the tool
tries to do more, as described with the predicate itself.
3.1. A Few Words about RDF
It is obviously not possible to give a full description of
RDF here, just a few words to make the essentials features
of what is described later understandable (again, the reader
is referred to the RDF Primer of W3C [14] for a more
systematic introduction to RDF).
An RDF file is a collection of simple statements of the
type “subject predicate object”. For example, the English
statement “Blackwell is the publisher of CGF” could be
described as:
• the subject is “Blackwell”
• the predicate is “publisher of”
• the object is “CGF”
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The following example (extracted from cgmarch.svg)
states that the slide contains four parts, identified
as MetafileStructure, PictureDetails,
PictureBody, and SymbolLibraries. Note that
here and in what follows the axsvg namespace prefix is
used to identify the linealizer predicates. This namespace
declaration is usually part of the enclosing rdf:RDF
element (see the examples for details).
<rdf:Description about"#SlideContent">
<axsvg:Contains>
<rdf:Bag>
<rdf:li rdf:resource="#MetafileStructure"/>
<rdf:li rdf:resource="#PictureDetails"/>
<rdf:li rdf:resource="#PictureBody"/>
<rdf:li rdf:resource="#SymbolLibraries"/>
</rdf:Bag>
</axsvg:Contains>
</rdf:Description>
The usage of rdf:Bag is optional:
<rdf:Description about="#SlideContent">
<axsvg:Contains resource="#MetafileStructure"/>
<axsvg:Contains resource="#PictureDetails"/>
<axsvg:Contains resource="#PictureBody"/>
<axsvg:Contains resource="#SymbolLibraries"/>
</rdf:Description>
However, by using rdf:Bag the linealizer tool can
produce a more structured output (turning the bag into a
bulleted list).
IsConvergencePoint
IsConnected
PointsTo
ExpandsTo
Associated All these predicates describe connections
between the subject and the object resources, often used in
presentation diagrams. The objects of these predicates are
often RDF bags.
The following example (again extracted from
cgmarch.svg) states that the resource Picture1 (which
is part of the MetafileStructure) “expands” to
PictureDetails, i.e. the latter give the details for the
former.
<rdf:Description about="#Picture1">
<axsvg:ExpandsTo rdf:resource="#PictureDetails"/>
</rdf:Description>
Connects This predicate is used when the subject is the
graphical “link” (i.e. line, curve, etc.) itself, and one wants
to describe which other objects are connected by the subject.
The immediate resource used by the predicate is usually an
rdf:Seq, conveying also the strict order of the connected
elements.
The following example (from network.svg) states that
the resource CableA, referring to a cable, connects the
computer to a socket.
<rdf:Description about="#CableA">
<axsvg:Connects>
<rdf:Seq>
<rdf:li rdf:resource="ComputerA"/>
<rdf:li rdf:resource="sock1"/>
</rdf:Seq>
</axsvg:Connects>
</rdf:Description>
IsDef The predicate states that the subject is a graphical
template defined either through the symbol element or
within a defs. The object of the predicate is the literal
true or false.
InstanceOf The predicate states that the subject is an
instance of a graphical template. The object of the predicate
is either an SVG resource (which is also identified as the
subject of an IsDef predicate), or a reified RDF statement
making use of the Symbol and the Transformation
predicates (see example below).
Symbol Identifies a template resource.
Transformation Describes the transformation applied
on the symbol when instantiating it. The object is either a
textual literal, describing the transformation, or a reference
to an SVG element. In the latter case the tool extracts the
transform attribute of the target and display it in the output.
The following example (extracted from svgtransfor-
mations.svg) contains three statements:
(1) The resource duck is a graphical template
(2) The resource Original is an instantiation of duck,
without specifying any transformation
(3) The resource simpleTranslate is also an instanti-
ation of duck, but translated to the (200,190) position.
<rdf:Description about="#duck">
<axsvg:IsDef>true</axsvg:IsDef>
</rdf:Description>
<rdf:Description about="#Original">
<axsvg:InstanceOf rdf:resource="#duck"/>
</rdf:Description>
<rdf:Description about="#simpleTranslate">
<axsvg:InstanceOf>
<rdf:Description>
<rdf:type
rdf:resource="http://www.w3.org/2001/svgRdf/
axsvg-resource.rdf#UseDescription"/>
<axsvg:Symbol rdf:resource="#duck"/>
<axsvg:Transformation>translate(200,190)
</axsvg:Transformation>
</rdf:Description>
</axsvg:InstanceOf>
</rdf:Description>
Note the usage of the rdf:type predicate. This pred-
icate refers to a more precise specification of the subject,
using RDF Schemas [15]. This predicate tells us that the
subject of the axsvg:InstanceOf predicate is an anony-
mous resource of a special type, describing the details of a
use SVG element.
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Text The predicate states that the subject is a textual node,
i.e. that the text content can be displayed directly. The
object of the predicate is the literal true or false. The
tool extracts the text from the SVG element and displays it
verbatim.
LabelledBy The predicate refers to an SVG resource or
a bag of resources which label the subject. The tool extracts
the text from the SVG element(s) and displays the content(s)
verbatim. If the object is a literal value, this is displayed
instead.
Labelled The predicate has the possible literal value of
true or false. In the former case the tool extracts the text
from the subject SVG element(s) and displays the content
verbatim.
The resources identified by these predicates are not
(necessarily) text nodes in the SVG sense. They can
be, for example, texts enclosed in groups or even more
complicated graphical objects, where only the textual parts
are meaningful for a non-visual environment.
The following example (extracted from svgtransfor-
mations.svg) identifies three textual elements used as
labels for scaleSkewXTranslate. The tool displays the
textual contents of the translate4, skew4, and scale4
elements.
<rdf:Description about="#scaleSkewXTranslate">
<axsvg:LabelledBy>
<rdf:Bag>
<rdf:li resource="#translate4"/>
<rdf:li resource="#skew4"/>
<rdf:li resource="#scale4"/>
</rdf:Bag>
</axsvg:LabelledBy>
</rdf:Description>
3.4. Layout and Positional Predicates
These predicates give an abstract description on the place-
ment of the various SVG objects relative to one another or
relative to the full canvas.
InPosition The predicate gives a rough absolute posi-
tion of the subject on the full canvas. The object of the pred-
icate is a literal with the possible value of N, S, W, E, NE, NW,
SE, SW, NNE, NNW, ENE, WNW, SSW, SSE, ESE, WSW, or
M, denoting 16 possible directions (north, south, west, east,
north-east, etc.) and the term “middle”.
InDirection Similar to InPosition, except that the
position of the subject is described relative to another object.
The object of the predicate is a reified statement using
RelativeTo and Direction.
RelativeTo Identifies an object used for InDirec-
tion.
Direction Refers to a direction value, used for InDi-
rection. The possible objects are identical to InPosi-
tion.
The following example (extracted from svgtrans-
formations.svg) states that Original is placed
in the middle of the full SVG viewport, and that
simpleTranslate is in a south-east direction of
Original.
<rdf:Description about="#Original">
<axsvg:InPosition>M</axsvg:InPosition>
</rdf:Description>
<rdf:Description about="#simpleTranslate">
<axsvg:InDirection>
<rdf:Description>
<rdf:type
rdf:resource="http://www.w3.org/2001/svgRdf/
axsvg-resource.rdf#DirectionDescription"/>
<axsvg:RelativeTo rdf:resource="#Original"/>
<axsvg:Direction>SE</axsvg:Direction>
</rdf:Description>
</axsvg:InDirection>
</rdf:Description>
IsGoingThrough
MaskedBy
InFrontOf
Behind
AtLeft
AtRight
OnTop
Under
HasOnTop
IsLayeredOn All these predicates can be used to provide
additional information of the object’s position relative to the
subject. Their role is quite clear.
3.5. Chart Predicates
These predicates are specific to chart-like figures.
ChartType The predicate describes the type of the chart.
Possible (literal) object values are: Bar, Line, Pie,
Scatter, Area, Doughnut, Radar, Bubble, Stock,
Surface. (The terms are those used by Microsoft Excel for
the generation of charts.)
Chart This predicate describes the important data
described by a chart. The object of the predicate is a special
resource using DataCategory and DataValues. (See
the example below.)
DataCategory The object of this predicate is either a
resource treated as a textual node, or a literal. It gives a user-
dependent characterization of the data set.
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DataValues The object of this predicate gives the real
data values. The object is either a literal (which contains
the real data) or another SVG object (in which case the tool
attempts to extract a desc object as a textual description of
the values).
The following example (extracted from member-
ship.svg) describes the three data lines which is central
to the chart; each has a category and a reference to a
resource. To make the example clearer, the SVG content for
totalMemberLine is also shown; the tool displays the
content of the desc element.
<rdf:Description about="#DataLines">
<axsvg:Chart>
<rdf:Bag>
<rdf:li>
<rdf:Description>
<rdf:type
rdf:resource="http://www.w3.org/2001/svgRdf/
axsvg-resource.rdf#ChartDescription"/>
<axsvg:DataCategory>
Total Members
</axsvg:DataCategory>
<axsvg:DataValues
rdf:resource="#totalMemberLine"/>
</rdf:Description>
</rdf:li>
<rdf:li>
<rdf:Description>
<rdf:type
rdf:resource="http://www.w3.org/2001/svgRdf/
axsvg-resource.rdf#ChartDescription"/>
<axsvg:DataCategory>
Full Members
</axsvg:DataCategory>
<axsvg:DataValues
rdf:resource="#fullMemberLine"/>
</rdf:Description>
</rdf:li>
<rdf:li>
<rdf:Description>
<rdf:type
rdf:resource="http://www.w3.org/2001/svgRdf/
axsvg-resource.rdf#ChartDescription"/>
<axsvg:DataCategory>
Affiliate Members</axsvg:DataCategory>
<axsvg:DataValues
rdf:resource="#affMemberLine"/>
</rdf:Description>
</rdf:li>
</rdf:Bag>
</axsvg:Chart>
</rdf:Description>
...
<path id="totalMemberLine" class="totalMembers"
d="M0 50
L50, 108 L100,117 L150,152
L200,158 L250,179 L300,231
L350,264 L400,293 L450,329
L500,363 L550,419 L600,478
L650,509">
<desc>50,108,117,152,158,179,231,264,293,329,
363,419,478,509</desc>
</path>
Unfortunately, this mechanism forces the author to write
the data twice: once for the coordinates in path and
once in the description. One could envisage an automatic
mechanism extracting the coordinate values from the path
directly, but the correct interpretation of the “d” attribute of
a path is not obvious (only the “Y” values are meaningful in
this example). Besides, other shape elements could also be
used, not only paths.
XLegend
YLegend
ZLegend Referring to the legend of the various chart axes.
If the object of the predicate is a SVG resource, it will be
interpreted similarly to a textual node.
3.6. Animation Predicates
These predicates describe the effects of animation objects on
other objects in SVG.
Animation objects in SVG have a relatively high
“granularity”: to perform a specific animation effect
one may have to use several SVG animation objects
whose combined effects are perceived by the user as one
animation. On a metadata level one should usually hide this
granularity. This means that while, in what follows, the term
“animation” or “animate” will be used in the sense used
in the SVG recommendation, “animation resource” might
also mean a group of animation objects, or an RDF resource
defined directly in the metadata section to describe an
animation effect.
AnimatedBy Refers to the fact that the subject is
animated (moved, deformed, etc.) by an animation object,
whose reference is the object of the predicate.
AnimationSubjects This predicate should be used
with a resource describing an animation; it refers to either
an SVG resource or a bag of resources which are affected by
the animation.
AnimationBegins
AnimationDuration Beginning and duration of an
animation. The object may refer to a literal or a “real”
SVG animation object; in the latter case the tool extracts
the begin (resp. dur) attribute of the SVG element (if it
exists). If a literal is used, one can add a general description
or refer to the formalism used in SVG for the begin (resp.
dur) attribute.
AnimationSeq
AnimationPar Although it is possible to describe the
full time line of the animations with the begin and duration
attributes, in a number of cases this is much too detailed.
AnimationSeq (resp. AnimationPar) lists a number
of animation resources which are executed in a sequence
(resp. in parallel). These are simplified versions of the SMIL
constructs [9,18].
The following example (extracted from PathAnima-
tion.svg) contains the animation on a simple path. Note
the usage of:
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• rdf:ID to identify a separate resource describing
animation, instead of referring to an SVG element. It
is sometimes quite useful to use this construction (i.e.
generate description elements which are not directly
bound to a specific SVG element).
• desc in conjunction with the #Animation resource.
If the RDF description is part of an SVG file the desc
is the same description element as elsewhere in the SVG
file, and can be used for a description (and reused by the
tool).
• rdf:type to make it sure that the resource is really
the description of the animation; this presupposes the
separate RDF Schema specification.
<rdf:Description rdf:about="#AnimatedDuck">
<axsvg:AnimatedBy rdf:resource="#Animation"/>
</rdf:Description>
<rdf:Description rdf:ID="#Animation">
<desc>
Deforms the duck into a potato and back
</desc>
<rdf:type
rdf:resource="http://www.w3.org/2001/svgRdf/
axsvg-resource.rdf#AnimationDescription"/>
<axsvg:AnimationSubjects
rdf:resource="#AnimatedDuck"/>
<axsvg:AnimationBegins>
user clicks on duck
</axsvg:AnimationBegins>
<axsvg:AnimationDuration>
2s
</axsvg:AnimationDuration>
</rdf:Description>
The following example (extracted from animw3c.svg)
is more complex, and describes the animation on the
spinning W3C logo and the disappearing domain logos.
Note that, instead of describing the detailed timing,
AnimationSeq is used. This is not absolutely precise,
because the fading out of the activity logos begin one second
before the end of the W3C logo spin, but this detail is not
really important if the tool is used to display the content of
the image textually.
<rdf:Description rdf:about="#opaciteimg2">
<axsvg:AnimationSubjects
rdf:resource="#domainLogos"/>
<axsvg:AnimationDuration>
2s
</axsvg:AnimationDuration>
</rdf:Description>
<rdf:Description rdf:ID="#logoAnimate">
<desc>
Spins around the logo by also reducing
its size to almost invisible
</desc>
<axsvg:AnimationSubjects rdf:resource="#W3CLogo"/>
<axsvg:AnimationDuration>
5s
</axsvg:AnimationDuration>
</rdf:Description>
<rdf:Description rdf:ID="#logoAnimate2">
<desc>
Scales the logo up to a reasonable size
</desc>
<axsvg:AnimationSubjects rdf:resource="#W3CLogo"/>
<axsvg:AnimationDuration>
4s
</axsvg:AnimationDuration>
</rdf:Description>
<rdf:Description rdf:ID="#animationTiming">
<rdf:type
rdf:resource="http://www.w3.org/2001/svgRdf/
axsvg-resource.rdf#AnimationDescription"/>
<desc>
Describes the relative timing of the animations
</desc>
<axsvg:AnimationSeq>
<rdf:Seq>
<rdf:li rdf:resource="#logoAnimate"/>
<rdf:li rdf:resource="#logoAnimate2"/>
<rdf:li rdf:resource="#opaciteimg2"/>
</rdf:Seq>
</axsvg:AnimationSeq>
<axsvg:AnimationBegins>
at load time
</axsvg:AnimationBegins>
</rdf:Description>
3.7. Miscalleneous Predicates
VisualEffects Refers to special filters, color gradient
fills, pattern fills, etc., which produce complex visual effects.
Most of these effects may simply be ignored in the metadata
description if the goal is to produce information for a
visually impaired user; if there is a necessity to refer to
the existence of these effects, the textual description should
suffice. This predicate simply binds an object to a subject
controlling the visual effects.
Shape Refers to the geometric shape of the subject; the
literal value can be rectangle, circle, etc., i.e. the
shapes defined by SVG. Note that the tool could extract,
for example, the shapes coordinates from the corresponding
SVG element, but it is not clear that this information would
really be meaningful.
In most of the cases, the shape itself does not convey any
important information on the content of the slide, so the
usage of that predicate might be less useful than one might
think at first.
4. The Linealizer Tool and its Future Developments
The current linealizer tool is a proof-of-concept
implementation rather than finished software. The first
version of the tool, by Lovet and Dardailler [6] was written
in Java, the current version is based on XSLT for easier
maintainability. The tool is restricted in its management
of resources: it can manage simple #id type of fragment
identifiers only, and only for elements in the same file
(i.e. the RDF metadata must be in the same SVG file).
A more elaborate version of the tool should include a
full URI management (which could lead to metadata
files “outside” the SVG source) as well as a full XPath
implementation to identify elements. Also, at present,
the RDF parser can only handle the basic serialization
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the object "#PictureN ( "A labelled box "Picture n")
the object "#EndMetafile ( "A labelled box "End Metafile")
The object is on top of "#PictureDetails ( "A series of labelled boxes)
Information on #Picture1
A labelled box "Picture 1"
The object expands to "#PictureDetails ( "A series of labelled boxes)
Information on #PictureDetails
A series of labelled boxes
The object contains:
the object "#BeginPicture ( "A labelled box "Begin Picture")
the object "#PictureDescriptor ( "A labelled box "Picture Descriptor")
the object "#PictureProperties ( "A labelled box "Begin Properties")
the object "#PictureBody ( "A labelled box "Begin Body")
the object "#EndPicture ( "A labelled box "End Picture")
The object points to "#Picture1 ( "A labelled box "Picture 1")
The object is on top of "#PictureBodyDetails ( "A series of labelled boxes)
Information on #PictureBody
A labelled box "Begin Body"
The object expands to "#PictureBodyDetails ( "A series of labelled boxes)
Information on #PictureBodyDetails
A series of labelled boxes
The object contains:
the object "#BeginPictureBody ( "A labelled box "Begin Picture Body")
the object "#GraphicsPrimitives ( "A box labelled with with graphics primitives)
the object "#EndPictureBody ( "A labelled box "End Picture Body")
The object points to "#PictureBody ( "A labelled box "Begin Body")
The object is on top of "#SymbolLibraries ( "A series of labelled boxes, much like a full metafile)
Information on #SymbolLibraries
A series of labelled boxes, much like a full metafile
The object points to "#GraphicsPrimitives ( "A box labelled with with graphics primitives)
Title of the slide: "Web CGM File structure"
This is a hierarchical representation of a WebCGM structure
Information on #SlideContent
The file structure of a full WebCGM file
The object contains:
the object "#MetafileStructure ( "A series of labelled boxes)
the object "#PictureDetails ( "A series of labelled boxes)
the object "#PictureBody (A labelled box "Begin Body")"
the object "#SymbolLibraries ( "A series of labelled boxes, much like a full metafile)
Information on #MetafileStructure
A series of labelled boxes
The object contains:
the object "#BeginMetafile ( "A box labelled "Begin Metafile")
the object "#MetafileDescriptor ( "A labelled box "Metafile Descriptor")
the object "#Picture1 ( "A labelled box "Picture 1")
the object "#Picture2 ( "A labelled box "Picture 2")
Figure 2: Representation of a WebGCM file structure.
Using the metadata included in this file, the generated
textual output (formatted as a simple HTML file) is shown
in Figure 2 (the text in italics is extracted from the user’s
description elements).
References
1. G.J. Bardos, J.J. Tirtowidjojo, K. Marriott, B Meyer,
W. Portnoy and A. Borning. A constraint extension to
scalable vector graphics. In Proceedings of The Tenth
International World Wide Web Conference. ACM Press,
2001.
2. T. Berners-Lee, J. Hendler and O. Lassila. The Semantic
Web. Scientific American, 2001.
3. D. Dardailler. Dependency statements for SVG. W3C
Note. Available at http://www.w3.org/WAI/
PF/dep-svg, February 2000.
4. D.A. Duce, I. Herman and F.R.A. Hopgood. Web
2D graphics file formats. Computer Graphics Forum,
21(1):43–64, 2002.
5. D.J. Duke and I. Herman. Minimal Graphics. IEEE
Computer Graphics & Application, 21(6), 2001.
A more detailed version is in: Reports of the
Centre for Mathematics and Computer Sciences,
INS-9903 (1999), ISSN 1386-3681, available at
http://www.cwi.nl/˜ivan/AboutMe/
Publications/INS-R9903.pdf.
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786 I. Herman and D. Dardailler / SVG Linearization and Accessibility
6. G. Lovet and D. Dardailler. SVG Linearizer tools.
W3C Note. Available at http://www.w3.org/
WAI/ER/ASVG/, September 2000.
7. A.M. MacEachren. How Maps Work. Guilford Press,
New York, 1995.
8. C. McCathieNevile and M-R. Koivunen. Accessibility
Features of SVG. W3C Note. Available at http://
www.w3.org/TR/SVG-access/, August 2000.
9. L. Rutledge. SMIL 2.0: XML for Web Multimedia.
IEEE Internet Computing, 5(5), 2001.
10. L. Rutledge, B. Bailey, J. van Ossenbruggen, L. Hard-
man and J. Geurts. Generating presentation constraints
from rhetorical structure. In Proceedings of the 11th
ACM conference on Hypertext and Hypermedia. ACM
Press, New York, 2000.
11. C. Ware. Information Visualization. Morgan Kaufman,
San Francisco, 2000.
12. IsaViz: A Visual Authoring Tool for RDF, http://
www.w3.org/2001/11/IsaViz/.
13. Resource description framework (RDF) model
and syntax. W3C Recommendation. Available at
http://www.w3.org/TR/REC-rdf-syntax/,
February 1999.
14. RDF Primer. W3C Working Draft. Available at http:
//www.w3.org/TR/rdf-primer/, April 2002.
15. RDF Vocabulary Description Language 1.0: RDF
Schema. W3C Working Draft. Available at http://
www.w3.org/TR/rdf-schema/, April 2002.
16. Saxon XSLT Processor. http://saxon.
sourceforge.net.
17. Scalable Vector Graphics (SVG) 1.0 Specification. W3C
Recommendation. Available at http://www.w3.
org/TR/SVG/, September 2001.
18. Synchronized Multimedia Integration Language (SMIL
2.0) Specification. W3C Recommendation. Available
at http://www.w3.org/TR/smil20/, August
2001.
19. Web Content Accessibility Guidelines 1.0. W3C Recom-
mendation. Available at http://www.w3.org/TR/
WAI-WEBCONTENT/, May 1999.
20. WebCGM Profile. W3C Recommendation. Available
at http://www.w3.org/TR/REC-WebCGM/,
January 1999.
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© The Eurographics Association and Blackwell Publishers Ltd 2002