root/standards/draft-pfeiffer-cmml-current.txt

Network Working Group                                        S. Pfeiffer
Internet-Draft                                                 C. Parker
Intended status: Informational                                   A. Pang
Expires: September 2, 2005                                         CSIRO
                                                              March 2005


        The Continuous Media Markup Language (CMML), Version 3.1
                         draft-pfeiffer-cmml-xx

Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of Section 3 of RFC 3667.  By submitting this Internet-Draft, each
   author represents that any applicable patent or other IPR claims of
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   RFC 3668.

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   This Internet-Draft will expire on September 2, 2005.

Copyright Notice

   Copyright (C) The IETF Trust (2005).











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Abstract

   This specification defines the Continuous Media Markup Language
   (CMML), version 3.1, an XML-based [XML] markup language for time-
   continuous data.  It is a sister document to the specification of the
   Annodex [ANX] annotation, indexing and hyperlinking format for time-
   continuous data.  A CMML file is essentially a textual representation
   of an Annodex file.

   The tags of a CMML file provide for the creation of structured and
   unstructured annotations as well as hyperlinks and addressable named
   anchor points for clips of time-continuous data.  Through its import
   tag, the CMML is also an authoring language for Annodex [ANX]
   streams.  The tag names in use in CMML are similar to the ones in
   XHTML [XHTML].

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [KEYWORDS].
































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  The CMML data types  . . . . . . . . . . . . . . . . . . . . .  7
     2.1.  ContentType  . . . . . . . . . . . . . . . . . . . . . . .  7
     2.2.  LinkTypes  . . . . . . . . . . . . . . . . . . . . . . . .  7
     2.3.  MediaDesc  . . . . . . . . . . . . . . . . . . . . . . . .  8
     2.4.  Text . . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     2.5.  URI  . . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     2.6.  LanguageCode . . . . . . . . . . . . . . . . . . . . . . .  9
     2.7.  Internationalisation support . . . . . . . . . . . . . . .  9
     2.8.  Time specifications  . . . . . . . . . . . . . . . . . . . 10
     2.9.  Core Attributes  . . . . . . . . . . . . . . . . . . . . . 10
   3.  The preamble and the 'cmml' root element . . . . . . . . . . . 11
   4.  The cmml 'stream' tag  . . . . . . . . . . . . . . . . . . . . 12
     4.1.  The 'import' tag . . . . . . . . . . . . . . . . . . . . . 13
     4.2.  The 'param' tag  . . . . . . . . . . . . . . . . . . . . . 14
   5.  The cmml 'head' element  . . . . . . . . . . . . . . . . . . . 16
     5.1.  The 'title' element  . . . . . . . . . . . . . . . . . . . 16
     5.2.  The 'base' element . . . . . . . . . . . . . . . . . . . . 17
     5.3.  The 'meta' element . . . . . . . . . . . . . . . . . . . . 17
     5.4.  The 'link' element . . . . . . . . . . . . . . . . . . . . 18
     5.5.  The 'style' element  . . . . . . . . . . . . . . . . . . . 18
   6.  The cmml 'clip' tag  . . . . . . . . . . . . . . . . . . . . . 20
     6.1.  The 'meta' element . . . . . . . . . . . . . . . . . . . . 21
     6.2.  The 'style' element  . . . . . . . . . . . . . . . . . . . 21
     6.3.  The 'a' element  . . . . . . . . . . . . . . . . . . . . . 21
     6.4.  The 'img' element  . . . . . . . . . . . . . . . . . . . . 22
     6.5.  The 'desc' element . . . . . . . . . . . . . . . . . . . . 22
     6.6.  The 'caption' element  . . . . . . . . . . . . . . . . . . 23
     6.7.  The 'p' element  . . . . . . . . . . . . . . . . . . . . . 23
     6.8.  The 'span' element . . . . . . . . . . . . . . . . . . . . 23
     6.9.  The 'br' element . . . . . . . . . . . . . . . . . . . . . 23
   7.  Serialising CMML . . . . . . . . . . . . . . . . . . . . . . . 25
     7.1.  The format of the CMML ident header packet . . . . . . . . 25
     7.2.  The format of the CMML secondary headers . . . . . . . . . 26
     7.3.  The format of the CMML data packets  . . . . . . . . . . . 27
   8.  Mapping CMML into Ogg and Annodex  . . . . . . . . . . . . . . 29
     8.1.  Media mapping for a CMML logical bitstream inside Ogg  . . 29
     8.2.  Using CMML to author Annodex bitstreams  . . . . . . . . . 30
       8.2.1.  Creating the skeleton ident packet . . . . . . . . . . 31
       8.2.2.  Creating the skeleton fisbone packets  . . . . . . . . 31
       8.2.3.  The CMML fisbone packet fields . . . . . . . . . . . . 32
       8.2.4.  Usage of the 'stream' tag  . . . . . . . . . . . . . . 33
   9.  Extracting CMML from Annodex bitstreams  . . . . . . . . . . . 35
     9.1.  Extracting the preamble, 'head' and 'clip' tags  . . . . . 35
     9.2.  Creating a 'stream' tag  . . . . . . . . . . . . . . . . . 35
   10. MIME media type registration for 'text/cmml' . . . . . . . . . 37



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     10.1. URI addressing into CMML files . . . . . . . . . . . . . . 37
       10.1.1. Query parameters for use with the http protocol
               server-side  . . . . . . . . . . . . . . . . . . . . . 38
       10.1.2. Fragment identifiers for use with the http
               protocol client-side . . . . . . . . . . . . . . . . . 39
   11. Security considerations  . . . . . . . . . . . . . . . . . . . 40
   12. ChangeLog  . . . . . . . . . . . . . . . . . . . . . . . . . . 41
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 42
   Appendix A.  CMML DTD  . . . . . . . . . . . . . . . . . . . . . . 44
   Appendix B.  An example CMML document  . . . . . . . . . . . . . . 45
   Appendix C.  Definitions of terms and abbreviations  . . . . . . . 47
   Appendix D.  Glossary of acronyms  . . . . . . . . . . . . . . . . 48
   Appendix E.  Acknowledgements  . . . . . . . . . . . . . . . . . . 49
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 50
   Intellectual Property and Copyright Statements . . . . . . . . . . 51




































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1.  Introduction

   The Continuous Media Markup Language (CMML) specifies XML based
   markup for time-continuous data to allow it to become an integral
   part of the World Wide Web analogously to how HTML allowed text
   documents to become part of the Web. Therefore, format of the CMML
   derives much from XHTML.

   CMML allows the attachment of free-text annotations, metadata,
   captions and other textual information to clips of time-continuous
   data.  This provides a timed, textual representation of the data that
   can be indexed by Web search engines.

   CMML also allows the attachment of a hyperlink to each clip of time-
   continuous data, enabling Web search engines to crawl the content.
   This also allows users to surf seamlessly between time-continuous
   data and other Web resources, integrating clips of media into the
   browsing history of a Web browser.

   CMML also provides a way of referencing a representative image for
   each clip of time-continuous data, providing a visual representation
   of the clip in conjunction with the textual representation.  The
   expected usage scenario for this is in the presentation of search
   results or in a table of clips.

   CMML provides a "head" element to store information that concerns the
   complete time-continous resource, and a set of "clip" elements that
   each store information for a temporal subpart of the resource.

   The practical use of a CMML file is in conjunction with the Annodex
   exchange format [ANX].  CMML markup can be interleaved inside an
   Annodex file or stream to allow a synchronised delivery of marked-up
   time-continuous data in a single stream between a Web server and a
   user agent.

   CMML has also been designed as an authoring language for Annodex
   bitstreams.  It allows the description of time-continuous data
   bitstream(s) that need to be multiplexed together to create an
   Annodex bitstream.  This information is stored in the "stream"
   element of a CMML document.  Such a document can be used to control
   the multiplexing process that creates an Annodex file.

   The following picture illustrates the multiplexing activity
   schematically; in reality, the stream tag is not preserved in its
   original form and some attribute values are also encoded in the
   binary data.  Details of how CMML markup is encoded in an Annodex
   bitstream are given later in this document.




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     ----------
     |stream  | CMML
     ---------- instance
     | head   | document
     ----------
     | clip_1 |     ----------------------------------------------------
     ----------     | data bitstream in packets                        |
     | ...    |     ----------------------------------------------------
     ----------          |
     | clip_n |          |
     ----------          |
         |               |
         ------->-<-------
                 |          Multiplexing
                 |
                 v
  ---------------------------------------------------------------------
  |stream|head|clip_1|  data packets         |clip_2| data packets  ...
  ---------------------------------------------------------------------

   The CMML is technically fully specified through its DTD as given in
   the Appendix.  The semantic meaning of each of the tags, their
   content and their attributes is specified in the following sections.
   The Appendix also contains an example of a CMML (instance) document.

   The file extension of CMML files is ".cmml".  This document also
   applies for registration of the mime-type "text/cmml" for CMML files
   with IANA.  In the meantime, "text/x-cmml" will be used.

   Please note that this document assumes that the reader has a fluent
   working knowledge of Extensible Markup Language (XML) [XML],
   Hypertext Markup Language (HTML) [HTML], XHTML [XHTML], Cascading
   Style Sheets (CSS) [CSS] and the World Wide Web. Basic knowledge
   about the Annodex [ANX] format is also assumed.

















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2.  The CMML data types

   At the beginning of the CMML DTD, several parameter entities are
   defined that are used throughout the DTD as data types.  This section
   gives a brief overview of them and refers to the relevant standards
   in which they are defined.

2.1.  ContentType

   A "ContentType" specifies the media type and subtype of a document as
   defined in RFC 2045 [ContentType].  It is used to specify the type of
   content that one input time-continuous bitstream contains.  Examples
   are "application/annodex", "audio/x-speex", "video/x-theora", or
   "video/mpeg".

2.2.  LinkTypes

   "LinkTypes" specifies a space-separated list of the types of
   relationships a linked, i.e. related, document has to the current
   one.  As in XHTML, user agents, search engines, etc. may interpret
   these link types in a variety of ways.  For example, user agents may
   provide access to linked documents through a navigation bar.  Authors
   may use the following recognized link types which are a superset of
   the ones used for XHTML/HTML:

   o  edit: Refers to a document that allows editing the resource.  This
      enables a document author to allow others to edit the CMML which
      is the basis for an Annodex resource.

   o  alternate: Designates substitute versions for the document in
      which the link occurs.  When used together with the media
      attribute, it implies a version designed for a different medium
      (or media).

   o  stylesheet: Refers to an external style sheet.

   o  start: Refers to the first document in a collection of documents.
      This link type tells search engines which document is considered
      by the author to be the starting point of the collection.

   o  next: Refers to the next document in a linear sequence of
      documents.  User agents may choose to pre-load the "next"
      document, to reduce the perceived load time.

   o  prev: Refers to the previous document in an ordered series of
      documents.





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   o  contents: Refers to a document serving as a table of contents.
      Although this may seem strange in a CMML file, it makes sense in
      an Annodex file and may simply refer back to the CMML file or to a
      HTML page that provides similar information.

   o  index: Refers to a document providing an index for the current
      document.

   o  glossary: Refers to a document providing a glossary of terms that
      pertain to the current document.

   o  copyright: Refers to a copyright statement for the current
      document.  While this could also be given in the meta tags, this
      could refer to a formatted, legal document.

   o  chapter: Refers to a document serving as a chapter in a collection
      of documents.

   o  section: Refers to a document serving as a section in a collection
      of documents.

   o  subsection: Refers to a document serving as a subsection in a
      collection of documents.

   o  appendix: Refers to a document serving as an appendix in a
      collection of documents.

   o  help: Refers to a document offering help (more information, links
      to other sources information, etc.)

   o  bookmark: Refers to a bookmark.  A bookmark is a link to a key
      entry point within an extended document.  The title attribute may
      be used, for example, to label the bookmark.  Note that several
      bookmarks may be defined in each document.

2.3.  MediaDesc

   A "MediaDesc" describes one or several types of devices for which the
   given style is appropriate.  It is given as a list of comma-separated
   media descriptors.  Which devices are supported will need to be
   specified in a separate style sheet specification.  The following set
   of device types, adapted from XHTML/HTML in CSS1, are recognized:

   o  all: suitable for all devices.

   o  aural: suitable for speech synthesizers.





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   o  braille: intended for braille tactile feedback devices.

   o  embossed: intended for paged braille printers.

   o  handheld: intended for handheld devices (characterized by a small,
      monochrome or colour display and limited bandwidth).

   o  print: intended for paged output to a printer or print preview on
      a screen.

   o  projection: intended for projected presentations (projectors or
      print to transparencies).

   o  screen: intended for non-paged, colour computer screens.

   o  tty: intended for fixed-pitch character grid displays (such as the
      teletypes or terminals).

   o  tv: for television-type devices with low resolution and limited
      scrollability.

2.4.  Text

   A "Text" describes a short, free form text being used for the "title"
   attribute.

2.5.  URI

   A "URI" is a character string that conforms to the specification of
   the Uniform Resource Identifier as defined in RFC 3986 [URI].  A URI
   generally points to a Web resource.  The URI time interval
   specification [timedURI] is supported for CMML and Annodex files.
   Also, direct addressing of clips as specified in the MIME type
   application part of this document is supported for CMML and Anndex
   files.

2.6.  LanguageCode

   The "LanguageCode" defines a collection of constant strings that each
   identify a specific language as defined in RFC 1766 [LANG].  Examples
   are: en-au, de, x-klingon.  Language codes are used to provide
   internationalisation support.

2.7.  Internationalisation support

   To provide international language support, the i18n entity draws
   together a language given by a "LanguageCode" in "lang" with the
   directionality of that language in "dir" given either as ltr (left-



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   to-right) or rtl (right-to-left). "ltr" is the default.

2.8.  Time specifications

   There are three different time specifications in use in CMML:
   "Timestamp", "Playbacktime" and "UTCtime".

   A "Timestamp" is generally a name-value pair which defines a time
   point.  The time point value is interpreted according to the time
   scheme given in the name.  If the name is ommitted, it defaults to
   "npt:".  Valid time schemes are the ones defined in the temporal URI
   specification [timedURI].

   The "Playbacktime" entity is a data type that just specifies a SMPTE
   or a NPT time.  It is therefore equal to the Timestamp entity without
   the UTC specification.

   The "UTCtime" entity is a data type that just specifies a UTC time
   without an identifier.  UTC time is specified as in the Timestamp
   entity, but without the "clock:" identifier.

2.9.  Core Attributes

   To cluster together the attributes that are common to most
   displayable elements, the "attrs" entity draws them together.  As
   "i18n" is already a cluster, a "coreattrs" entity is defined, which
   groups together the other commonly used attributes for displayable
   elements, namely the unique identifier given in "id", the "class"
   attribute which provides a space-separated list of style sheet
   classes that the element belongs to, and the "title" attribute, which
   provides a short tooltip-like description for an element.




















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3.  The preamble and the 'cmml' root element

   A CMML file is an XML instance document of the CMML DTD.  An example
   is given in the Appendix.  It starts with the usual xml directive and
   the DTD specification (see
   http://www.w3.org/TR/REC-xml#sec-prolog-dtd).  The following is an
   example preamble:

   <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
   <!DOCTYPE cmml SYSTEM "cmml.dtd">

   After the preamble, the CMML tag follows.  A CMML file has a "cmml"
   tag as the root element.  It embraces all the other tags.

   <!ELEMENT cmml (stream?, head, clip*)>
   <!ATTLIST cmml
     %i18n;
     id          ID             #IMPLIED
     xmlns       %URI;          #FIXED 'http://www.annodex.net/cmml'
     granulerate CDATA          #IMPLIED
     >

   The "cmml" tag encloses at most one "stream" element, exactly one
   "head" element, and as many "clip" elements as the document author
   requires.  A "clip" element describes a section of the related
   Annodex bitstream.

   Attributes of the "cmml" element are the usual xml root tag
   attributes: the internationalisation attributes "lang" and "dir", an
   identifier "id", a fixed namespace "xmlns", and the "granulerate".

   The internationalisation attributes specify the default language
   (language and directionality) of the complete CMML document.  If not
   given, the language default adheres to the same rules as HTML, where
   the setting of the HTTP "Content-Language" header may specify the
   default language of a HTML document received over HTTP, or ultimately
   the user agent defaults and user preferences set the language. (see
   http://www.w3.org/TR/REC-html40/struct/dirlang.html)

   Every element has an "id" attribute.  The value of the "id" attribute
   MUST be unique within the document.  It allows to uniquely identify
   an instance of an element and address it.

   The "granulerate" attribute may provide a base temporal resolution
   for the CMML bitstream.  This is in particular used for creation of
   Annodex files from a given CMML instance document.





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4.  The cmml 'stream' tag

   The "stream" element contains information that is used for authoring
   Annodex [ANX] bitstreams from existing time-continuous data.  The
   Annodex bistream is created by multiplexing the bitstreams given in
   the "src" attributes of the "import" tags of the "stream" element
   together with the CMML annotations in a time-synchronous manner.

   The "stream" element describes in the "import" tags the input time-
   continuous bitstreams that are to be multiplexed together on
   authoring the Annodex bitstream.  Its attributes describe other
   features of the Annodex bitstream such as the time mappings for the
   start of the file.

   <!ELEMENT stream (import*)>
   <!ATTLIST stream
     id          ID             #IMPLIED
     basetime    %Playbacktime; "0"
     utc         %UTCtime;      #IMPLIED
     >

   The "stream" element has no text attributes and thus
   internationalisation attributes are not required.  The "id" attribute
   follows the default language specified in the "cmml" element.

   The "basetime" attribute contains a playback time in seconds
   associated with the first data packet of the Annodex bitstream.  All
   other times in the CMML file MUST be calculated relative to this
   basetime.  For example, a basetime of 300 seconds npt for a video
   file implies that the first frame is related to a play time of 300
   seconds, and a clip with a start time of 350 seconds is to be
   included 50 seconds into the Annodex bitstream.  If no basetime (or
   no stream tag) is given, the basetime defaults to 0 npt.  The
   basetime can be given as a SMPTE or NPT time, or as a rational number
   as in 5/1300, but not as a utc time.

   The "utc" attribute associates a calendar date and a wall-clock time
   with the basetime.  It therefore provides a mapping of the basetime
   to a real-world clock time and is given as a UTC time.  If it is
   omitted, the start attribute in the import tag, and the start and end
   attributes in clip tags MUST NOT be specified as UTC times.

   The content model of the "stream" tag then proposes an arbitrary
   number of input bitstreams.  These are described one by one in the
   "import" element.






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4.1.  The 'import' tag

   A "import" tag contains information on one of the input bitstreams
   for the multiplexing process.  It may also contain additional
   parameters to set up the Annodex encoder for each import bitstream.

   <!ELEMENT import (param*)>
   <!ATTLIST import
     %i18n;
     id          ID             #IMPLIED
     granulerate CDATA          #IMPLIED
     contenttype %ContentType;  #IMPLIED
     src         %URI;          #REQUIRED
     start       %Timestamp;    "0"
     end         %Timestamp;    #IMPLIED
     title       CDATA          #IMPLIED
     >

   The relevant bitstream (fragment) is referenced through the "src"
   attribute.  The src is a URI and may thus also contain a time
   interval specification in URIs which narrows down the input file to
   that given subpart.  That resource is multiplexed into the Annodex
   bitstream starting at the time given in the "start" attribute and
   ending at the latest at the time given in the "end" attribute.  The
   "start" and "end" attributes are interpreted relative to the timeline
   of the Annodex bitstream.

   The internationalisation attributes provide the language of the
   import element's and the contained param tags' attribute values, such
   as the "id" attributes and the "title" attribute.

   The "granulerate" attribute contains the base temporal resolution in
   Hz of the input bitstream referred in the "src" attribute.  It
   depends on the encoding format of the input bitstream and typically
   contains the framerate for video (e.g. 25 frames/sec) and the
   samplerate for audio (e.g. 44100 samples/sec), but may contain any
   rational number given with an integer denominator larger than 1 sec
   (e.g. 25 frames on 2 seconds).  Each bitstream has its own
   granulerate dependent on its specific encoding.  This attribute is
   implied as it can be determined automatically during the multiplexing
   process from the headers of the encoded media bitstream.  For
   bitstreams without header, such as uncompressed audio, the author of
   the CMML file can provide the granulerate to the multiplexer in this
   attribute.

   The "contenttype" attribute specifies the media type [ContentType] of
   the input bitstream referred in the "src" attribute.  It is optional
   as the media type can often be derived from the file name or file



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   header of the media source during multiplexing.

   The "src" attribute specifies a URI to the input bitstream.  Commonly
   used URI schemes are "file" and "http".  For specifying temporal
   subsets of the input bitstream, use the time interval specification
   for URIs [timedURI].

   The "start" attribute specifies a time in the output Annodex
   bitstream at which the media bitstream will be inserted.  This time
   is specified with respect to the "basetime" attribute given in the
   "stream" element.

   The "end" attribute specifies a time in the output Annodex bitstream
   at which the media bitstream will stop at the latest.  This time is
   also specified with respect to the "basetime" attribute given in the
   "stream" element.  This attribute is not required when the full
   bitstream is used.

   The optional "title" attribute provides a chance to jot down a human
   readable comment on the source bitstream.  This may e.g. be used in
   authoring applications for a more human readable display than the
   "id" tag which is really a key for identifying elements uniquely.

   The content model of the "import" tag then allows an arbitrary number
   of "param" tags to add as many descriptive parameter values to the
   mulitplexing activity as necessary.

4.2.  The 'param' tag

   A "param" tag is empty, but its attributes contain a name-value pair
   for describing the input bitstream in the parent "import" element.
   It inherits its internationalisation from that element, too, to avoid
   overhead.  The "param" element is declared as follows:

   <!ELEMENT param EMPTY>
   <!ATTLIST param
     id          ID             #IMPLIED
     name        CDATA          #REQUIRED
     value       CDATA          #REQUIRED
     >

   The "name" attribute identifies a property name.  It does not list
   legal values for this attribute.

   The "value" attribute specifies a property's value.  It does not list
   legal values for this attribute.

   An example parametrisation is the provision of machine-processable



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   low level meta information about the import bitstream such as a
   video's image height and width and framerate.

















































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5.  The cmml 'head' element

   The CMML "head" element contains annotation information on the
   complete Annodex bitstream, for whose creation the CMML file is used.
   It therefore contains header-type information such as a title, style
   information, related documents and meta information describing the
   bitstream.

   The "head" element is declared as the following:

   <!ENTITY % head.misc "(style|meta|link)*">

   <!ELEMENT head (%head.misc;,
                   ((title, %head.misc;, (base, %head.misc;)?) |
                   (base, %head.misc;, (title, %head.misc;))))>
   <!ATTLIST head
     %i18n;
     id          ID             #IMPLIED
     profile     %URI;          #IMPLIED
     >

   The "head" tag must contain a "title" tag.  It may contain one "base"
   tag before or after the "title" tag and any number of "style",
   "meta", or "link" tags at any position.

   The "%i18n;" attribute specifies the base language of the "head"
   tag's attribute values.

   The value of the "profile" attribute is a space-separated list of
   base URIs specifying locations of "meta" tag schemes such as the
   Dublin Core (see http://dublincore.org/).  These schemes may be used
   in the "meta" elements of the "head" or the "clip" tags.

5.1.  The 'title' element

   The "title" tag gives a descriptive title for the complete Annodex
   bitstream.  It is not considered to be part of the presentation and
   should be displayed, e.g. as the title of the window that the Annodex
   bitstream is being displayed in.  Exactly one title is required per
   document.  The "title" element is declared as the following:

   <!ELEMENT title (#PCDATA)>
   <!ATTLIST title
     %i18n;
     id          ID       #IMPLIED
   >

   The "%i18n;" attribute specifies the base language of the "title"



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   text.

5.2.  The 'base' element

   The "base" element defines the base URI of the Annodex bitstream.
   All relative URIs of the bitstream get interpreted relative to this
   base.  The "base" element is empty, but its attributes contain the
   base URI.  It is declared as follows:

   <!ELEMENT base EMPTY>
   <!ATTLIST base
     id      ID       #IMPLIED
     href    %URI;    #REQUIRED
   >

   The "href" attribute contains the base URI.  If the "base" element is
   omitted, the base URI of the Annodex bitstream is derived from the
   address through which the Annodex bitstream is accessed.

5.3.  The 'meta' element

   The "meta" element in the "head" element defines structured
   annotations for the complete Annodex bitstream.  A "meta" element is
   empty, but its attributes contain the name-value pairs of a
   structured annotation.  The "meta" element is declared as follows:

   <!ELEMENT meta EMPTY>
   <!ATTLIST meta
     %i18n;
     id       ID       #IMPLIED
     name     NMTOKEN  #IMPLIED
     content  CDATA    #REQUIRED
     scheme   CDATA    #IMPLIED
   >

   The "%i18n;" attribute specifies the language of the meta attribute
   and content texts.

   The "name" attribute identifies a property name.  It does not list
   legal values for this attribute.

   The "content" attribute specifies a property's value.  It does not
   list legal values for this attribute.

   The "scheme" attribute names a scheme to be used to interprete the
   property's value.  The scheme can be located via the "profile"
   attribute in the "head" element.




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5.4.  The 'link' element

   The "link" element in the "head" element defines links to a related
   external resource.  These resources are often used to augment the
   user agent's ability to process the current document.  The "link"
   element is declared as follows:

   <!ELEMENT link EMPTY>
   <!ATTLIST link
     %attrs;
     href        %URI;          #IMPLIED
     type        %ContentType;  #IMPLIED
     rel         %LinkTypes;    #IMPLIED
     rev         %LinkTypes;    #IMPLIED
     media       %MediaDesc;    #IMPLIED
     >

   The "attrs;" attribute covers the specification of the language of
   the title attribute, a unique identifing name, a reference to a style
   sheet specification, and a title attribute to provide a short
   description of the relationship between the current document and the
   one referred to in the "href" attributed.

   The "href" attribute contains a URI reference to a related external
   resource.  These resources are often used to augment the user agent's
   ability to process the current document.

   The "type" attribute contains a media type specification for the
   linked document as per RFC 2045 [ContentType], e.g. "text/
   x-css-cmml".

   The "rel" attribute describes the relationship from the current
   document to the resource specified by the href attribute.  The value
   of this attribute is a space-separated list of link types.

   The "rev" attribute describes a reverse link from the resource
   specified by the href attribute to the current document.  The value
   of this attribute is a space-separated list of link types.

   The "media" attribute specifies the intended destination device for
   style information, if the href points to an external style sheet.  It
   may be a single media descriptor or a comma-separated list.  The
   default value for this attribute is "screen".

5.5.  The 'style' element

   The "style" element in the "head" element contains an internally
   defined style sheet.  The "style" element is declared as follows:



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   <!ELEMENT style (#PCDATA)>
   <!ATTLIST style
     %i18n;
     id          ID             #IMPLIED
     title       %Text;         #IMPLIED
     type        %ContentType;  #REQUIRED
     media       %MediaDesc;    #IMPLIED
     xml:space   (preserve)     #FIXED 'preserve'
     >

   The "i18n;" attribute containt the language of the title attribute.

   The "title" attribute contains a short description of the style in
   human readable form.

   The "type" attribute contains a media type specification for the
   linked document as per RFC 2045 [ContentType], e.g. "text/
   x-css-cmml".

   The "media" attribute specifies the intended destination device for
   the style information.  It may be a single media descriptor or a
   comma-separated list.  The default value for this attribute is
   "screen".




























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6.  The cmml 'clip' tag

   A CMML file typically contains a number of sections given through
   "clip" tags.  The CMML "clip" tag contains information about a
   section of the Annodex bitstream.  This is expressed in a number of
   elements and attributes annotating, indexing, and hyperlinking the
   section.  The "start" and "end" attributes are used to give the
   insertion time for the clip into the Annodex bitstream.

   <!ELEMENT clip ((meta|style)*, a?, img?, desc?, caption?)>
   <!ATTLIST clip
     %attrs;
     track       CDATA          "default"
     start       %Timestamp;    #REQUIRED
     end         %Timestamp;    #IMPLIED
     >

   Any number of "meta" or "style" elements may appear in a clip, and at
   most one "a" element, one "img" element, and one "desc" element.
   Though "meta", "style", "a", "img", and "desc" tag are given in a
   specific order in the DTD, their order is actually random.

   The "%i18n;" attributes part of the "%attrs;" attributes specify the
   base language for all the clip's attribute values and content
   elements.  Also, a unique identifying name is specified for the clip
   in the "id" attribute.  This name can be used in URIs that point
   either to the CMML file or the Annodex bitstream created from it, and
   allows to point straight at the clip.  This may either be done as a
   URI fragment or URI query specification.  The "class" attribute
   provides a space-separated list of style sheet classes, and the
   "title" attribute a short tooltip-like clip description.

   The "track" attribute specifies the track that this clip belongs to.
   An annotation track is a set of clips that belong together from a
   semantic point of view.  Clips in the same track must not overlap
   temporally.  A default track must be available always.  This track is
   the one a client (such as a Web browser plugin) will display by
   default.  Other annotation tracks may be created by the document
   author to describe a more specific content.  An example use are
   different annotation tracks for each speaker in an audio recording of
   a meeting or tracks of different languages.

   The "start" and "end" attributes specify the time range during which
   the clip element is defined.  This time range is specified with
   respect to the "basetime" and "utc" attributes given in the "stream"
   tag.  If the "stream" tag does not contain a "utc" specification,
   "start" and "end" times are not allowed to be given in UTC time.
   "start" is a required attribute because a clip without a start time



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   is useless. "end" is optional and only required where clips cannot
   continue on to the following clip.

6.1.  The 'meta' element

   The "meta" element is specified above in the "head" section.  While a
   "meta" element in the "head" tag provides meta information for the
   complete Annodex bitstream, the "meta" elements in a "clip" tag only
   provide meta information for the clip.

6.2.  The 'style' element

   The "style" element is specified above in the "head" section.  While
   a "style" element in the "head" tag provides style sheet information
   for the complete Annodex bitstream, the "style" elements in a "clip"
   tag only provide style sheet information for the clip.

6.3.  The 'a' element

   The "a" element specifies a link to a related Web resource together
   with some information on that related resource.  The "a" element
   definition is very closely related to the xhtml "a" element
   definition with a reduced number of attributes as they make sense for
   time-continuous data.

   <!ELEMENT a (#PCDATA)>
   <!ATTLIST a
     %attrs;
     href        %URI;          #REQUIRED
     >

   The "attrs" attributes specify internationalisation of the anchor's