Fw: intra-document hyperlink

[Hironobu Takagi <TAKAGIH@jp.ibm.com>]

I will attach Ishihara-san's investigation
on the intra-document link issue.

Malte, 
Is there any documentation for the rule
of fragment identifier in OpenOffice.org? 

---------------------
Hironobu Takagi, PhD.
User Experience and Accessibility Technology
Tokyo Research Laboratory, IBM Research
+81-46-215-4557
E-mail: takagih@jp.ibm.com


----- Forwarded by Hironobu
Takagi/Japan/IBM on 2007/04/24 10:49 -----
---
Tatsuya Ishihara 
IBM Tokyo Research Laboratory (Mail Code: LAB-S77)
E-mail : tisihara@jp.ibm.com
Tel: +81-46(215)4978     Fax: +81-46(274)4282

-----
Summary
------------------

Current ODF documents have an
interoperability issue for hyperlink which refers to ODF elements within
same document (intra-document links).
This issue is caused by two reasons.

1. URI syntax of intra-document
link is not defined in ODF spec.

2. In OpenOffice, a URI of intra-document
link to a heading element involves text content of the heading element.
        e.g.
"#5. Introduction|outline"
        denotes "5th heading in this document,
and the text contents is 'Introduction' "
  This implementation will
cause interoperability issues, since this type of use of fragment identifier
(notation after # in URI) is not popular among office editors and browsers.
 

Intra-document link is important
for improving accessibility of documents, since it allows users to jump
to intended part of document directly. (e.g. table of contents)
We propose to define syntax of
intra-document links ("fragment" part in URI) in the ODF spec,
in order to point unique ODF element without ambiguity.


Detail
------------------

There is a interoperability problem
that implementation of hyperlink for headings or graphics within same document
is different in office applications.

Blind users access documents
by using screen readers. They move cursor by keyboard command and reads
the line where cursor is located.
To find out what they need in
the text document, they have to move through the cursor 
and read the contents from the
top of the documents. If intra-document links are inserted, screen readers
can skip the contents and jump to intended part of document.
This function is often used in
"Table of Contents" function. So hyperlinks within same document
is necessary to improve accessibility.


This is an example file created
by OpenOffice.org v2.2.


Hyperlink URI is shown by moving
the mouse pointer over text link.
An example of hyperlink URI for
heading area is like this.

"#5.Introduction|outline"

It means that "5th heading
in this document, and the text contents is 'Introduction' ".

This URI is ambiguous. If a heading
with same text content is inserted before the heading referred by this
hyperlink,
this hyperlink refer to the new
heading.

The URI should point one ODF
element clearly, and ODF should define this specification for
ensuring the interoperability.

In ODF 1.1 specification, URI
of hyperlink is defined by "xlink:href" attribute of <text:a>
element.
ODF 1.1 defines hyperlink URI
as follows.

-----------------------
ODF 1.1 page 91
Link Location
The xlink:href attribute specifies
the URL for the target location of the link.
-----------------------

Current XLink specification is
here.
http://www.w3.org/TR/xlink/

"xlink:href" attribute
in XLink specification is defined as follows.
This attribute should have URI
value.

-------------------------------
5.4 Locator Attribute (href)
The value of the href attribute
must
be a URI reference as defined in [IETF
RFC 2396], or must
result in a URI reference 
after the escaping procedure
described below is applied. The procedure is applied when passing the URI
reference to a URI resolver. 
-------------------------------

RFC 2396 is obsoleted by latest
URI specification.
Latest specification of URI (RFC
3986) is here. 
http://www.ietf.org/rfc/rfc3986.txt

URI specification says that the
subset of resource is specified by "fragment".
"fragment" and "same-document
reference" is defined as follows.
It says that fragment's format
is dependent on each media type.

---------------------------
3.5.  Fragment

 Fragment identifier semantics
are independent of the URI scheme and 
thus cannot be redefined by scheme
specifications. Individual media 
types may define their own restrictions
on or structures within the 
fragment identifier syntax for
specifying different types of subsets, 
views, or external references
that are identifiable as secondary resources by that media type.

4.4.  Same-Document Reference

   When a URI reference refers to a URI that is, aside from its fragment
   component (if any), identical to the base URI (Section 5.1), that
   reference is called a "same-document" reference.  The
most frequent
   examples of same-document references are relative references that
are
   empty or include only the number sign ("#") separator
followed by a
   fragment identifier.
---------------------------

So ODF should define syntax of
hyperlink URI for same document area.

ODF specification has id functions
like "draw:name", or "text:name". 
We had better use these attribute
for this purpose.

----------------------------
OpenOffice 2.2 implementation

<text:a xlink:href=""#5.Introduction|outline">jump"
to title</text:a>
....
<text:h>Introduction</text:h>

<text:a xlink:href=""#graphics1|graphics">jump"
to image</text:a>
...
<draw:frame draw:style-name="fr1"
draw:name="graphics1" text:anchor-type="paragraph"
svg:x="0.268cm" svg:y="0.721cm" svg:width="3.394cm"
svg:height="2.545cm" draw:z-index="0">
  <draw:image xlink:href=""Pictures/1000000000000A6B000007D0BBB2CD79.jpg""
xlink:type="simple" xlink:show="embed" xlink:actuate="onLoad"/>
</draw:frame>
----------------------------

----------------------------
Proposal

<text:a xlink:href=""#heading1">jump"
to title</text:a>
....
<text:h text:name="heading1">Title
Contents</text:h>

<text:a xlink:href=""#graphics1">jump"
to image</text:a>
....
<draw:frame draw:style-name="fr1"
draw:name="graphics1" text:anchor-type="paragraph"
svg:x="0.268cm" svg:y="0.721cm" svg:width="3.394cm"
svg:height="2.545cm" draw:z-index="0">
  <draw:image xlink:href=""Pictures/1000000000000A6B000007D0BBB2CD79.jpg""
xlink:type="simple" xlink:show="embed" xlink:actuate="onLoad"/>
</draw:frame>
----------------------------

HeadingLinkOOo.odt