Edit comment LC-2367 for Efficient Extensible Interchange Working Group

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Comment LC-2367

Comment Shortname:

Commenter: FABLET Youenn <Youenn.Fablet@crf.canon.fr>

Message-id:

Section of the document concerned:

[Free text description]Document as a whole1. Introduction 2. Design Principles 3. Basic Concepts 4. EXI Streams 5. EXI Header 5.1 EXI Cookie 5.2 Distinguishing Bits 5.3 EXI Format Version Example 5-1. EXI Format Version Examples 5.4 EXI Options 6. Encoding EXI Streams 6.1 Determining Event Codes 6.2 Representing Event Codes 6.3 Fidelity Options 7. Representing Event Content 7.1 Built-in EXI Datatype Representations 7.1.1 Binary 7.1.2 Boolean 7.1.3 Decimal 7.1.4 Float 7.1.5 Integer 7.1.6 Unsigned Integer Example 7-1. Example algorithm for decoding an Unsigned Inte... 7.1.7 QName 7.1.8 Date-Time 7.1.9 n-bit Unsigned Integer 7.1.10 String 7.1.10.1 Restricted Character Sets 7.1.11 List 7.2 Enumerations 7.3 String Table 7.3.1 String Table Partitions 7.3.2 Partitions Optimized for Frequent use of Compact Identifiers 7.3.3 Partitions Optimized for Frequent use of String Literals 7.4 Datatype Representation Map Example 7-2. datatypeRepresentationMap indicating all Decima... Example 7-3. datatypeRepresentationMap illustrating a user-d... 8. EXI Grammars 8.1 Grammar Notation 8.1.1 Fixed Event Codes Example 8-1. Example productions with fixed event codes 8.1.2 Variable Event Codes Example 8-2. Example productions that use macro non-terminal... Example 8-3. Example non-terminal macros and its productions... Example 8-4. Expanded productions equivalent to the producti... 8.2 Grammar Event Codes Example 8-5. Example productions with event codes 8.3 Pruning Unneeded Productions Example 8-6. Example productions with full fidelity Example 8-7. Example productions after pruning 8.4 Built-in XML Grammars 8.4.1 Built-in Document Grammar 8.4.2 Built-in Fragment Grammar 8.4.3 Built-in Element Grammar 8.5 Schema-informed Grammars 8.5.1 Schema-informed Document Grammar 8.5.2 Schema-informed Fragment Grammar 8.5.3 Schema-informed Element Fragment Grammar 8.5.4 Schema-informed Element and Type Grammars 8.5.4.1 EXI Proto-Grammars 8.5.4.1.1 Grammar Concatenation Operator 8.5.4.1.2 Element Grammars 8.5.4.1.3 Type Grammars 8.5.4.1.3.1 Simple Type Grammars 8.5.4.1.3.2 Complex Type Grammars 8.5.4.1.3.3 Complex Ur-Type Grammar 8.5.4.1.4 Attribute Uses 8.5.4.1.5 Particles 8.5.4.1.6 Element Terms 8.5.4.1.7 Wildcard Terms 8.5.4.1.8 Model Group Terms 8.5.4.1.8.1 Sequence Model Groups 8.5.4.1.8.2 Choice Model Groups 8.5.4.1.8.3 All Model Groups 8.5.4.2 EXI Normalized Grammars 8.5.4.2.1 Eliminating Productions with no Terminal Symbol 8.5.4.2.2 Eliminating Duplicate Terminal Symbols 8.5.4.3 Event Code Assignment 8.5.4.4 Undeclared Productions 8.5.4.4.1 Adding Productions when Strict is False 8.5.4.4.2 Adding Productions when Strict is True 9. EXI Compression 9.1 Blocks 9.2 Channels 9.2.1 Structure Channel 9.2.2 Value Channels 9.3 Compressed Streams 10. Conformance 10.1 EXI Stream Conformance 10.2 EXI Processor Conformance A.1 Normative References A.2 Other References B Infoset Mapping C XML Schema for EXI Options Document D Initial Entries in String Table Partitions E Deriving Set of Characters from XML Schema Regular Expressions F Content Coding and Internet Media Type G Example Encoding (Non-Normative) H Schema-informed Grammar Examples (Non-Normative)
or

Refinement of the section concerned:

Status:

open proposal pending resolved_yes resolved_no resolved_partial other assigned to Nobody Bournez, Carine Brutzman, Don Cokus, Michael Fernández, Javier D. Heuer, Joerg Käbisch, Sebastian Kamiya, Takuki Kuntschke, Richard Matsukura, Ryuichi McGregor, Don Peintner, Daniel Quin, Liam Shah, Grishma ZERGAOUI, Mohamed

Type: substantive editorial typo question general comment undefined

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No response from Commenter yet Commenter approved disposition Commenter objected to disposition
Commenter's response (URI):

Comment:

Dear all,

Based on internal feedback, I would like to make the following observations on the current EXI specification.
Note that this is not a request for change of the EXI specification.
I think however that this may be of some use/interest for the community.

Currently, all attributes of an XML element are stored by EXI encoders before being actually written.
This is a different behavior from text XML writers that can write attributes as soon as applications provide them.
In some environments, this attribute storage behavior has a real processing cost that does not appear with traditional StAX-like text XML writers.

There are two main technical reasons for storing attributes:

- In schema mode, it is better to give specific attributes order so as to get good compression

- @xsi:type and/or @xsi:nil must appear first in schema and schemaless modes
The first reason is a strong reason. I also note that EXI enables some flexibility in the attribute ordering if that better suits the application needs. This seems very reasonable as this added flexibility does not impact performances nor interoperability.

The second reason seems weaker since, at least in our scenarios, @xsi:type/@xsi:nil do not appear very often anyway.
It would have been good to have the flexibility to put @xsi:type and @xsi:nil in the order desired by applications.
Of course, this would need changing the way these attributes actually impact on the EXI grammars.
I did not do the full exercise, but I am confident that there are some reasonably simple workarounds that would get us back to a similar functionality level anyway.

The advantages would have been:

- No more special attribute behavior handling at the codec runtimes level

o General spec simplification

o Smaller and potentially faster EXI codec runtimes

- Performances improvement by enabling streamed encoding of attributes

o At least in the case of built-in grammars but also in schema-deviation mode

o More consistent with some text XML writer behavior

Regards,
Youenn

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WG Notes:

Resolution: http://lists.w3.org/Archives/Public/public-exi-comments/2010Jun/0000.html

(Please make sure the resolution is adapted for public consumption)