rfc767.txt
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TXT
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external data, the information necessary to gain access to the
external data, and the information necessary to apply the correct
interpretation to the external data. For example, this might
include:
name description
---- -----------
NET network name
HOST host name
FILE file name
USER user name (computer account name)
PASSWORD password
ACCOUNT account
FORMAT format
Port
The address of MPM within the host. Represented by a name element.
Presentation Descriptor
A property list of <name,value> pairs, where the name is an order
indicator, and the value is a presentation element. The order
indicators are SEQUENTIAL, SIMULTANEOUS, and INDEPENDENT.
Presentation Element
A property list of media structures.
Protocol
The name of the coding scheme used for a medium. Represented by a
name element.
References
The message identifiers of other messages. Represented by a list of
text elements.
Reply-To
A list of mailboxes. Sometimes it will be desired to direct the
replies of a message to some address other than the from or the
sender. In such a case the reply-to object can be used.
Postel [Page 11]
August 1980
A Structured Format for Transmission of Multi-Media Documents
Specification
R 450 Block
The unit of Rapicom 450 data (585 bits). Represented by a bitstr
element.
Sender
A mailbox. The sender will contain the address of the individual
who sent the message. In some cases this is NOT the same as the
author of the message. Under such a condition, the author should be
specified in the from object.
SID
An NLS statement indetifier. Represented by a integer element.
State
A state name. Represented by a name element.
Subject
The subject of the message. Represented by a text element.
Text Structure
A text data structure. Represented by a property list.
To
A list of mailboxes. To identifies the addressees of the message.
User
A user name (computer account name). Represented by a name element.
Version
A version number. Represented by a index element.
Vocoder
A vocoder name. Represented by a name element.
Voice Structure
A voice data structure. Represented by a property list.
[Page 12] Postel
August 1980
A Structured Format for Transmission of Multi-Media Documents
Specification
X121 Address
This identifies a host in the Public Data Network environment. When
used as a part of identifier, it identifies the originating host of
a message. The X121 address is a sequence of up to 14 digits [23].
For use in this format the X121 address is represented in decimal
digits.
ZIP
A zip code. Represented by a name element.
2.3. Body Structures
2.3.1. Simple Elements
The body could simply be a single data element. For example a
single text element can represent a lengthy character string.
<body> := TEXT
or
text:"this is the actual text of the body"
2.3.2. Structured Text
The body could be thought of as paragraphs, where each paragraph is
represented by a text element. The paragraphs are then the elements
of a list.
<body> := LIST (<paragraph>, <paragraph>, ...)
<paragraph> := TEXT
or
list:(text:"paragraph one", text:"paragraph two", ...)
2.3.3. NLS File Example
It is possible to represent the data from NLS files in this format.
NLS is a large multipurpose system which operates on structured data
files. The files are tree structured, and there is data associated
with each node of the tree. There are several fields associated
with each node as well.
Postel [Page 13]
August 1980
A Structured Format for Transmission of Multi-Media Documents
Specification
An NLS file is:
proplist( file
name:"FILENAME", name:<file> name of file
name:"CREATION-DATE", name:<date> creation date and time
name:"VERSION", index:<version> file version number
name:"SID-COUNT", integer<count> current SID count
name:"LAST-WRITER", name:<ident> last writer of file
name:"OWNER", name:<ident> owner of file
name:"LAST-WRITE-TIME", name:<date> last write date and time
name:"LEFT-NAME-DELIM-DEFAULT", name:<c> default name
name:"RIGHT-NAME-DELIM-DEFAULT", name:<c> delimiters
name:"SUBSTRUCTURE", <nls-substructure> substructure
)endlist
An NLS substructure is:
list:( substructure
<nls-node> node is defined below
.
.
.
)endlist
An NLS node is:
proplist:( node
name:"BLOCK", <nls-block> block defined below
name:"SUBSTRUCTURE", <nls-substructure> substructure
)endlist
An NLS block is:
proplist:( block
name:"LEFT-NAME-DELIM", name:<c> left name delimiter
name:"RIGHT-NAME-DELIM", name:<c> right name delimiter
name:"SID", integer:<sid> SID number
name:"CREATOR", name:<ident> statement creator
name:"CREATION-TIME", name:<date> creation date and time
name:"DATA", <data> data defined below
)endlist
[Page 14] Postel
August 1980
A Structured Format for Transmission of Multi-Media Documents
Specification
NLS data is:
proplist:( data
name:"<a data name>", <type depends on data name>
. .
. .
. .
)endlist
For text, data is:
proplist:( data
name:"TEXT", text:"text of statement" text
)endlist
2.3.4. Multimedia Structures
One can conceive of graphical information being displayed along with
a running commentary, much as seminars use slides. A slide and its
description are tied together. The coordination of such a
presentation is central to its understanding. This synchronization
should be captured within the document structure.
There are three fundamentally different types of time ordered
control which are needed within the document structure. These are:
Simultaneous
Sequential
Independent
Simultaneous data is intended for synchronous presentation. The
implication is that this data is presented in parallel.
Sequential data items will be presented one at a time, in the order
listed. The ordering is strictly left to right.
Independent data can be presented in any time order. It is not
ordered in any manner.
The data is broken into small information units called presentation
elements or PEs. The PEs can be combined in structures to control
the presentation order. A PE is a property list of elements
representing information of various media. For example:
<pe> := proplist(
name:"VOICE", <voice-structure>,
name:"GRAPHICS", <graphics-structure>
)endlist
Postel [Page 15]
August 1980
A Structured Format for Transmission of Multi-Media Documents
Specification
PEs are combined into larger controled presentations by
presentation-descriptors or PDs. A PD is a property list which
specifies the type of time ordering of the PEs in its list.
<pd> := <<seq>> | <<sim>> | <<ind>>
<<seq>> := name:"SEQUENTIAL", <pe>
<<sim>> := name:"SIMULTANEOUS", <pe>
<<ind>> := name:"INDEPENDENT", <pe>
A PE is a property list of the media <name,value> pairs, or PDs.
<pe> := <<text>> | <<voice>> | <<facsimile>>
| <<graphics>> | <pd>
<<text>> := name:"TEXT", <text structure>
<<voice>> := name:"VOICE", <voice structure>
<<facsimile>> := name:"FACSIMILE", <facsimile structure>
<<graphics>> := name:"GRAPHICS", <graphics structure>
If more than one <name,value> pair is present within a PE the media
are presented on different output devices in the order specified by
the PE's parent PD. The order of appearance within the proplist is
important only in the event that the parent PD specified sequential
ordering.
The structure of multimedia messages which use this scheme will be
demonstrated by a few simple examples chosen to illustrate a basic
text document and the different ordering options. The last example
will suggest some more exotic uses.
[Page 16] Postel
August 1980
A Structured Format for Transmission of Multi-Media Documents
Specification
Plain Text Message
A simple text body could be represented in a single text data
structure. To give the simplest example of a structured body we
show a simple text body represented in the multimedia structure.
<body> := <pd>
<pd> := <<seq>>
<<seq>> := name:"SEQUENTIAL", <pe>
<pe> := name:"TEXT", <text structure>
or
proplist: (name:"SEQUENTIAL",
proplist:(
name:"TEXT", <text structure>
)endlist
)endlist
Simultaneous Ordering
This ordering option is used to indicate when separate streams are
to be presented in parallel. For example, assume GRAPHICS and
VOICE data were to be presented using simultaneously.
<body> := <pd>
<pd> := <<sim>>
<<sim>> := name:"SIMULTANEOUS", <pe>
<pe> := name:"VOICE", <voice structure>
name:"GRAPHICS", <graphics structure>
or
proplist:(
name:"SIMULTANEOUS",
proplist:(
name:"VOICE", <voice structure>
name:"GRAPHICS", <graphics structure>
)endlist
)endlist
Postel [Page 17]
August 1980
A Structured Format for Transmission of Multi-Media Documents
Specification
Sequential Ordering
This option is used to indicate sequential time ordering. The
media in the sub-tree below this PD are not separate streams.
Using again the example above, assume GRAPHICS and VOICE data were
to be presented using sequential ordering.
<body> := <pd>
<pd> := <<seq>>
<<seq>> := name:"SEQUENTIAL", <pe>
<pe> := name:"VOICE", <voice structure>
name:"GRAPHICS", <graphics structure>
or
proplist:(
name:"SEQUENTIAL",
proplist:(
name:"VOICE", <voice structure>
name:"GRAPHICS", <graphics structure>
)endlist
)endlist
Independent Ordering
It is apparent that some output devices are very slow in
comparison to others. An example which demonstrates this is
facsimile. The majority of facsimile devices are slow. A
detailed picture transmitted at 9600 baud takes minutes to print.
It is inconvenient for the user to wait on such a device when the
voice or text information which accompanies it is short.
For example, if the document a facsimile image and the text
"Hello Frank, here's a copy of that picture you requested." The
user need not wait for the picture. The facsimile machine might
be spooled, in which case he would pick up the picture later. In
a sense the picture was time independent of the text.
[Page 18] Postel
August 1980
A Structured Format for Transmission of Multi-Media Documents
Specification
<body> := <pd>
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