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[DFXP LC Comment] SYMM WG Comments on DFXP 1.0 LCWD

From: Yoshihisa Gonno <ygonno@sm.sony.co.jp>
Date: Mon, 25 Apr 2005 22:24:32 +0900
Message-ID: <426CEF90.2080608@sm.sony.co.jp>
To: public-tt@w3.org
CC: W3C SYMM <symm@w3.org>

Dear TTWG,

On behalf of SYMM WG, I would like to say thank you for extending the
review period of DFXP 1.0 LCWD.  SYMM WG has eagerly reviewed DFXP 1.0
LCWD and prepared our comments.  SYMM WG hopes these comments will be
used to improve the Timed Text specification.
Please accept our official comments on DFXP 1.0 LCWD from SYMM WG.

SYMM WG Comments on DFXP 1.0 LCWD

0. Overall / General

SYMM-0-1: The SYMM WG is concerned about large scale duplication of
functionality of existing W3C specifications in the DFXP LC WD document:
The DFXP specification describes functionality that is already defined
by other specifications, such as XHTML, CSS, and SMIL.
   DFXP should re-use these specifications. It should do this without
introducing any changes to the syntax or semantics in these
specifications; whole units of related functionality  should be adopted.
  To make re-use of an existing spec clearer to the reader and to avoid
making any changes the DFXP specification should reference to the
original specification instead of including an own description of such a
   It may extend these existing languages whenever its own requirements
exceed what is already available.  This will be of benefit to content
authors because they do not need to learn a new language. It will also
be helpful for implementation of processors because they can re-use
software components.

1. Introduction

SYMM-1-1: The functional distinction between DFXP and AFXP seems
unclear.  It's hard to understand why there should be two different
profiles.  It just appears to be complicating the system model.  The
functional difference between DFXP and AFXP should be explained more
formally than Figure 1.

SYMM-1-2: The current draft does not mention any specific example to
explain what kind of legacy formats can be transcoded and how much
useful that is.  The potential markets and application areas should be
introduced more specifically.

SYMM-1-3: SYMM WG believes DFXP should primarily serve the purpose to be
rendered directly i.e. it should not be required to first transcode DFXP
into a proprietary format for rendering.  DFXP should therefore be
specified as a distribution format.
   It should be designed to be delivered to and rendered by a wide range
of desktop, embedded and mobile terminals.  Such distribution format for
TT should integrate well at least with SMIL and XHTML.
   Preferably, the DFXP specification should define in full the
integration to SMIL and to XHTML to achieve full interoperability.

3. Conformance

SYMM-3-1: The specification insufficiently defines rules for processing
and rendering of DFXP content.

5. Vocabulary

SYMM-5-1: It is not visible which vocabulary was newly invented by DFXP
or introduced from existing standards such as XHTML, CSS, XSL, SMIL.
The original references of all vocabularies should be arranged in a
table for readability.

6. Parameters

SYMM-6-1: The parameters for time metric seems to have improved very
well and sufficient to associate with wide variety of media materials.
But it would be helpful to understand them correctly if more specific
examples for each feature were provided.

7. Content

SYMM-7-1: It appears to be a bad choice to re-define HTML language
elements div, span, p, br with different semantics as in XHTML.  XHTML
syntax and semantics should be adopted without making any changes.

SYMM-7-2: Allowing the root tt element to have timing and styling
attributes seems redundant.  The right place to hold default values of a
document would be the body element.

8. Styling

SYMM-8-1: CSS and XSL:FO are the W3C standards for styling and layout.
Also DFXP should use CSS or XSL:FO for styling.  It should use both
exact syntax and semantics of CSS/XSL:FO, and then define its own
attributes where CSS/XSL specifications are insufficient.  Chosen
solution must allow a lightweight implementation on constraint embedded
   In case that CSS is used for styling, it is not good enough to use
CSS attribute names DFXP, e.g. tt:display, tt:fontFamily.  CSS syntax
and semantics should be used without changes.  DFXP spec should list the
CSS properties it supports and reference to CSS 2.1 spec for their
definition.  To get the CSS working normally and leverage its full power
the DFXP spec may also adopt the following CSS 2.1 features by
referencing to CSS 2.1 specs:
* syntax and basic data types
* selectors
* assigning property values, Cascading, and Inheritance
* media types (with possible restriction of the supported media types )

SYMM-8-2: (8.3.12) <namedColor> should reference some other
specification.  Stable references should be CSS2.

9. Layout

SYMM-9-1: CSS and XSL are the W3C standards for styling and layout.
Also DFXP should use either CSS, XSL or SMIL layout.  DFXP may define
its own attributes where CSS/XSL/SMIL specifications are insufficient.
Chosen solution must allow a lightweight implementation on constraint
embedded devices.

SYMM-9-2: Allowing timing attributes to be placed in layout elements
seems interesting, but it could complicate timing structure of a
document.  Its necessity should be explained reasonably.

SYMM-9-3: Allowing style elements to be placed as a child of a region
element seems redundant.  Allowing style attributes to be placed in a
region element would be sufficient.

10. Timing

SYMM-10-1: DFXP should use a subset of the SMIL 2 Timing and
Synchronization Module functionality.  It should use exact syntax and
semantics of SMIL.

12. Metadata

SYMM-12-1: The metadata attributes should be introduced from or
reference  to industry standards or existing specifications.  DFXP
should not develop its own attribute set as a normative part of a

SYMM-12-2: The places for metadata should be limited within a head
element.  SMIL already provides a good example:

Appendix B: Dynamic Flow Processing Model

SYMM-B-1: Text and diagram should be provided.

Appendix H: Acknowledgments

SYMM-H-1: Listing former/inactive members seems inappropriate. (It looks
like accusing specific individuals.) That paragraph should be removed.

Best regards,

Yoshihisa Gonno, Sony Corporation
Co-chair W3C SYMM WG
email: ygonno@sm.sony.co.jp
Received on Monday, 25 April 2005 13:24:50 UTC

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