About XML Compression and MPEG-7

[Claude Seyrat <cseyrat@acland.fr>]

Dear All,

Regarding the compression aspect of XML, i would like to 
mention that currently MPEG experts are working on a standard 
(MPEG-7) about audiovisual metadata carriage and processing.

In MPEG-7 metadata are expressed in XML. XML Schema is used to 
define datastructures. A large library of types are defined to 
describe many aspect of a multimedia document ranging from low 
level features (colors, movement, etc..) to high level description 
(RDF like).

XML descriptions can be sent as a whole or synchronously streamed
within the AV stream (MPEG-2 or MPEG-4). In MPEG-7, XML can be 
easily encoded, streamed, and filtered.

For that purpose MPEG-7 designed a binary encoding format very 
similar to what you are suggesting and to ASN-1 (but far more 
XML oriented). The codec is dynamically generated based on the 
schema expressed in XML Schema. It accepts every XML Schema 
features like substitutionGroups, sub-typing, choices, sequences, 
aso...

Compression ratios show that elements can be represented by few bits
in average (sometimes less than one bit), values are coded using 
specific datatype encodings. 

Best regards,
Claude.

-- 
______________________________________________

Claude Seyrat

Expway c/o Acland
18 avenue Georges V
75008 Paris
tel: 33 1 56 62 11 05
fax: 33 1 56 62 11 11
mail: cseyrat@acland.fr