Xqueeze: Compact XML Alternative

Xqueeze Specifications

About this document
- Terms of Use
- GNU Free Documentation License
xqML language (0.1.0)
- xqML Symbols
- Formal xqML (0.1.0) Grammar in EBNF notation

About this document

This document contains the specifications for xqML language (0.1.0), xqML Symbols, Xqueeze Association format (0.1.0) and Xqueeze Association algorithm (0.1.0) that together comprise the Xqueeze package.

© 2002 Xqueeze Developers
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in section 1.2 entitled ``GNU Free Documentation License''.

Terms of Use

Usage of the Specification in this document for developing an Implementation is subject to the following terms and conditions:

An Implementation advertizing itself to be based on the Specification should support the provisions of the Specification in whole or partially, provided it also fulfils condition 4.
An Implementation advertizing itself to be conforming to the Specification should put into effect the provisions of the Specification in whole.
The Specifications may be modified and re-distributed according to the provisions of GNU FDL (§1.2).
An Implementation must not advertize itself to be based on or conforming to the Specification if it is based on a modification of the Specification unless such modifications are also distributed under the terms of GNU FDL (§ 1.2) or compatible license.
Items 1 through 4 of these terms of use only apply to specifications and implementations that are distributed commercially or non-commercially to the public.

Glossary

Specification: The document or documents as designated by the Original Contributor that defines the form, interface and semantics to the technology covered by the contents of the Specification.
Implementation: An implementation of the specification is a program or set of programs that puts into effect the form, interface and semantics defined by the Specification.
Modification: Any deletion, addition or alteration to the form, interface or semantics defined by the Specification.
Original Contributor: The initiator of the Specification.

GNU Free Documentation License

		GNU Free Documentation License
		  Version 1.2, November 2002


 Copyright (C) 2000,2001,2002  Free Software Foundation, Inc.
     59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 Everyone is permitted to copy and distribute verbatim copies
 of this license document, but changing it is not allowed.


0. PREAMBLE

The purpose of this License is to make a manual, textbook, or other
functional and useful document "free" in the sense of freedom: to
assure everyone the effective freedom to copy and redistribute it,
with or without modifying it, either commercially or noncommercially.
Secondarily, this License preserves for the author and publisher a way
to get credit for their work, while not being considered responsible
for modifications made by others.

This License is a kind of "copyleft", which means that derivative
works of the document must themselves be free in the same sense.  It
complements the GNU General Public License, which is a copyleft
license designed for free software.

We have designed this License in order to use it for manuals for free
software, because free software needs free documentation: a free
program should come with manuals providing the same freedoms that the
software does.  But this License is not limited to software manuals;
it can be used for any textual work, regardless of subject matter or
whether it is published as a printed book.  We recommend this License
principally for works whose purpose is instruction or reference.


1. APPLICABILITY AND DEFINITIONS

This License applies to any manual or other work, in any medium, that
contains a notice placed by the copyright holder saying it can be
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A "Modified Version" of the Document means any work containing the
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The "Invariant Sections" are certain Secondary Sections whose titles
are designated, as being those of Invariant Sections, in the notice
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The "Cover Texts" are certain short passages of text that are listed,
as Front-Cover Texts or Back-Cover Texts, in the notice that says that
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A "Transparent" copy of the Document means a machine-readable copy,
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format whose markup, or absence of markup, has been arranged to thwart
or discourage subsequent modification by readers is not Transparent.
An image format is not Transparent if used for any substantial amount
of text.  A copy that is not "Transparent" is called "Opaque".

Examples of suitable formats for Transparent copies include plain
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The "Title Page" means, for a printed book, the title page itself,
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A section "Entitled XYZ" means a named subunit of the Document whose
title either is precisely XYZ or contains XYZ in parentheses following
text that translates XYZ in another language.  (Here XYZ stands for a
specific section name mentioned below, such as "Acknowledgements",
"Dedications", "Endorsements", or "History".)  To "Preserve the Title"
of such a section when you modify the Document means that it remains a
section "Entitled XYZ" according to this definition.

The Document may include Warranty Disclaimers next to the notice which
states that this License applies to the Document.  These Warranty
Disclaimers are considered to be included by reference in this
License, but only as regards disclaiming warranties: any other
implication that these Warranty Disclaimers may have is void and has
no effect on the meaning of this License.


2. VERBATIM COPYING

You may copy and distribute the Document in any medium, either
commercially or noncommercially, provided that this License, the
copyright notices, and the license notice saying this License applies
to the Document are reproduced in all copies, and that you add no other
conditions whatsoever to those of this License.  You may not use
technical measures to obstruct or control the reading or further
copying of the copies you make or distribute.  However, you may accept
compensation in exchange for copies.  If you distribute a large enough
number of copies you must also follow the conditions in section 3.

You may also lend copies, under the same conditions stated above, and
you may publicly display copies.


3. COPYING IN QUANTITY

If you publish printed copies (or copies in media that commonly have
printed covers) of the Document, numbering more than 100, and the
Document's license notice requires Cover Texts, you must enclose the
copies in covers that carry, clearly and legibly, all these Cover
Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on
the back cover.  Both covers must also clearly and legibly identify
you as the publisher of these copies.  The front cover must present
the full title with all words of the title equally prominent and
visible.  You may add other material on the covers in addition.
Copying with changes limited to the covers, as long as they preserve
the title of the Document and satisfy these conditions, can be treated
as verbatim copying in other respects.

If the required texts for either cover are too voluminous to fit
legibly, you should put the first ones listed (as many as fit
reasonably) on the actual cover, and continue the rest onto adjacent
pages.

If you publish or distribute Opaque copies of the Document numbering
more than 100, you must either include a machine-readable Transparent
copy along with each Opaque copy, or state in or with each Opaque copy
a computer-network location from which the general network-using
public has access to download using public-standard network protocols
a complete Transparent copy of the Document, free of added material.
If you use the latter option, you must take reasonably prudent steps,
when you begin distribution of Opaque copies in quantity, to ensure
that this Transparent copy will remain thus accessible at the stated
location until at least one year after the last time you distribute an
Opaque copy (directly or through your agents or retailers) of that
edition to the public.

It is requested, but not required, that you contact the authors of the
Document well before redistributing any large number of copies, to give
them a chance to provide you with an updated version of the Document.


4. MODIFICATIONS

You may copy and distribute a Modified Version of the Document under
the conditions of sections 2 and 3 above, provided that you release
the Modified Version under precisely this License, with the Modified
Version filling the role of the Document, thus licensing distribution
and modification of the Modified Version to whoever possesses a copy
of it.  In addition, you must do these things in the Modified Version:

A. Use in the Title Page (and on the covers, if any) a title distinct
   from that of the Document, and from those of previous versions
   (which should, if there were any, be listed in the History section
   of the Document).  You may use the same title as a previous version
   if the original publisher of that version gives permission.
B. List on the Title Page, as authors, one or more persons or entities
   responsible for authorship of the modifications in the Modified
   Version, together with at least five of the principal authors of the
   Document (all of its principal authors, if it has fewer than five),
   unless they release you from this requirement.
C. State on the Title page the name of the publisher of the
   Modified Version, as the publisher.
D. Preserve all the copyright notices of the Document.
E. Add an appropriate copyright notice for your modifications
   adjacent to the other copyright notices.
F. Include, immediately after the copyright notices, a license notice
   giving the public permission to use the Modified Version under the
   terms of this License, in the form shown in the Addendum below.
G. Preserve in that license notice the full lists of Invariant Sections
   and required Cover Texts given in the Document's license notice.
H. Include an unaltered copy of this License.
I. Preserve the section Entitled "History", Preserve its Title, and add
   to it an item stating at least the title, year, new authors, and
   publisher of the Modified Version as given on the Title Page.  If
   there is no section Entitled "History" in the Document, create one
   stating the title, year, authors, and publisher of the Document as
   given on its Title Page, then add an item describing the Modified
   Version as stated in the previous sentence.
J. Preserve the network location, if any, given in the Document for
   public access to a Transparent copy of the Document, and likewise
   the network locations given in the Document for previous versions
   it was based on.  These may be placed in the "History" section.
   You may omit a network location for a work that was published at
   least four years before the Document itself, or if the original
   publisher of the version it refers to gives permission.
K. For any section Entitled "Acknowledgements" or "Dedications",
   Preserve the Title of the section, and preserve in the section all
   the substance and tone of each of the contributor acknowledgements
   and/or dedications given therein.
L. Preserve all the Invariant Sections of the Document,
   unaltered in their text and in their titles.  Section numbers
   or the equivalent are not considered part of the section titles.
M. Delete any section Entitled "Endorsements".  Such a section
   may not be included in the Modified Version.
N. Do not retitle any existing section to be Entitled "Endorsements"
   or to conflict in title with any Invariant Section.
O. Preserve any Warranty Disclaimers.

If the Modified Version includes new front-matter sections or
appendices that qualify as Secondary Sections and contain no material
copied from the Document, you may at your option designate some or all
of these sections as invariant.  To do this, add their titles to the
list of Invariant Sections in the Modified Version's license notice.
These titles must be distinct from any other section titles.

You may add a section Entitled "Endorsements", provided it contains
nothing but endorsements of your Modified Version by various
parties--for example, statements of peer review or that the text has
been approved by an organization as the authoritative definition of a
standard.

You may add a passage of up to five words as a Front-Cover Text, and a
passage of up to 25 words as a Back-Cover Text, to the end of the list
of Cover Texts in the Modified Version.  Only one passage of
Front-Cover Text and one of Back-Cover Text may be added by (or
through arrangements made by) any one entity.  If the Document already
includes a cover text for the same cover, previously added by you or
by arrangement made by the same entity you are acting on behalf of,
you may not add another; but you may replace the old one, on explicit
permission from the previous publisher that added the old one.

The author(s) and publisher(s) of the Document do not by this License
give permission to use their names for publicity for or to assert or
imply endorsement of any Modified Version.


5. COMBINING DOCUMENTS

You may combine the Document with other documents released under this
License, under the terms defined in section 4 above for modified
versions, provided that you include in the combination all of the
Invariant Sections of all of the original documents, unmodified, and
list them all as Invariant Sections of your combined work in its
license notice, and that you preserve all their Warranty Disclaimers.

The combined work need only contain one copy of this License, and
multiple identical Invariant Sections may be replaced with a single
copy.  If there are multiple Invariant Sections with the same name but
different contents, make the title of each such section unique by
adding at the end of it, in parentheses, the name of the original
author or publisher of that section if known, or else a unique number.
Make the same adjustment to the section titles in the list of
Invariant Sections in the license notice of the combined work.

In the combination, you must combine any sections Entitled "History"
in the various original documents, forming one section Entitled
"History"; likewise combine any sections Entitled "Acknowledgements",
and any sections Entitled "Dedications".  You must delete all sections
Entitled "Endorsements".


6. COLLECTIONS OF DOCUMENTS

You may make a collection consisting of the Document and other documents
released under this License, and replace the individual copies of this
License in the various documents with a single copy that is included in
the collection, provided that you follow the rules of this License for
verbatim copying of each of the documents in all other respects.

You may extract a single document from such a collection, and distribute
it individually under this License, provided you insert a copy of this
License into the extracted document, and follow this License in all
other respects regarding verbatim copying of that document.


7. AGGREGATION WITH INDEPENDENT WORKS

A compilation of the Document or its derivatives with other separate
and independent documents or works, in or on a volume of a storage or
distribution medium, is called an "aggregate" if the copyright
resulting from the compilation is not used to limit the legal rights
of the compilation's users beyond what the individual works permit.
When the Document is included an aggregate, this License does not
apply to the other works in the aggregate which are not themselves
derivative works of the Document.

If the Cover Text requirement of section 3 is applicable to these
copies of the Document, then if the Document is less than one half of
the entire aggregate, the Document's Cover Texts may be placed on
covers that bracket the Document within the aggregate, or the
electronic equivalent of covers if the Document is in electronic form.
Otherwise they must appear on printed covers that bracket the whole
aggregate.


8. TRANSLATION

Translation is considered a kind of modification, so you may
distribute translations of the Document under the terms of section 4.
Replacing Invariant Sections with translations requires special
permission from their copyright holders, but you may include
translations of some or all Invariant Sections in addition to the
original versions of these Invariant Sections.  You may include a
translation of this License, and all the license notices in the
Document, and any Warrany Disclaimers, provided that you also include
the original English version of this License and the original versions
of those notices and disclaimers.  In case of a disagreement between
the translation and the original version of this License or a notice
or disclaimer, the original version will prevail.

If a section in the Document is Entitled "Acknowledgements",
"Dedications", or "History", the requirement (section 4) to Preserve
its Title (section 1) will typically require changing the actual
title.


9. TERMINATION

You may not copy, modify, sublicense, or distribute the Document except
as expressly provided for under this License.  Any other attempt to
copy, modify, sublicense or distribute the Document is void, and will
automatically terminate your rights under this License.  However,
parties who have received copies, or rights, from you under this
License will not have their licenses terminated so long as such
parties remain in full compliance.


10. FUTURE REVISIONS OF THIS LICENSE

The Free Software Foundation may publish new, revised versions
of the GNU Free Documentation License from time to time.  Such new
versions will be similar in spirit to the present version, but may
differ in detail to address new problems or concerns.  See
http://www.gnu.org/copyleft/.

Each version of the License is given a distinguishing version number.
If the Document specifies that a particular numbered version of this
License "or any later version" applies to it, you have the option of
following the terms and conditions either of that specified version or
of any later version that has been published (not as a draft) by the
Free Software Foundation.  If the Document does not specify a version
number of this License, you may choose any version ever published (not
as a draft) by the Free Software Foundation.


ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and
license notices just after the title page:

    Copyright (c)  YEAR  YOUR NAME.
    Permission is granted to copy, distribute and/or modify this document
    under the terms of the GNU Free Documentation License, Version 1.2
    or any later version published by the Free Software Foundation;
    with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
    A copy of the license is included in the section entitled "GNU
    Free Documentation License".

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts,
replace the "with...Texts." line with this:

    with the Invariant Sections being LIST THEIR TITLES, with the
    Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.

If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.

If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License,
to permit their use in free software.

xqML language (0.1.0)

xqML is the binary markup language that is used by Xqueeze to achieve compact document sizes as compared to XML documents. xqML is structurally very similar to XML. The greatest contributors to xqML's compact nature are the elimination of redundant information and representation of XML identifiers (NMTOKENs) whose definitions are available in the DTD/Schema with binary xqML Symbols.

xqML Symbols

xqML Symbols are octect sequences that represent unsigned integers written in MSB (Most Significant Byte first) order. Additionally, the least significant bit of each octet of a symbol, except the last one, should be one. For example, the integer 256 can be a valid xqML Symbol since when written in MSB order, it's bit pattern is [00000001 00000000]. Thus the least significant bit of each octet in the symbol acts as a continuation flag. A 1 indicates that the next octet is a part of the symbol, a 0 indicates the end.

It is trivial that all xqML Symbols must be even numbers. Additionally, one bit of each octet is rendered unusable since it acts as a continuation flag. 16 bit xqML Symbols can represent 16384 different identifiers while 32 bit ones can represent over 268 million different identifiers. A conforming implementation is required to support atleast 16 bit long symbols.

xqML Symbols start from 0x02 (decimal 2) and symbols up to 0xFE (decimal 254) are reserved for special purposes. Higher values are available for generating associations using the Xqueeze Association algorithm. While associating a symbol with an identifier, its type is also stored. Thus, a symbol represents not only the string literal, but also the type of an identifier.

Formal xqML (0.1.0) Grammar in EBNF notation

document ::= prolog element Misc* 
prolog ::= xqMLDecl? Misc* (doctypedecl Misc*)? 
xqMLDecl ::= '<{0x02}xqml-' Num 
Misc ::= Comment 
doctypedecl ::= '<{0x12}' DoctypeName '<' | xqA
element ::= (EE_STag | STag) content ETag? 
EE_STag ::= '<' EESymbol (Attribute)* 
STag ::= '<' ELSymbol (Attribute)* 
content ::= CharData? ((element | Reference | CDSect | Comment) CharData?)* 
Attribute ::= '<' ATSymbol CharData '<' | '<' APSymbol VASymbol 
Reference ::= EntityRef | CharRef 
EntityRef ::= '<' ENSymbol 
CharRef ::= '&{0x26}'Num;
CDSect ::= CDDelim (.* - (.* CDDelim .*) CDDelim 
CDDelim ::= '<{0x14}' 
Comment ::= '<{0x22}' CharData ETag? 
ETag ::= '<{0x3E}' ElementsToClose 
Num ::= [0-9.]+ 
CharData ::= [^<&]*

Terminals:

Figures enclosed within braces ({}): are hex codes for the value of an xqML Symbol that should occur within.
DoctypeName: is a string literal identifying a document type
xqA: is the Xqueeze Association (without preamble)
ELSymbol: is an xqML Symbol of the type ``element''
EESymbol: is an xqML Symbol of the type ``empty element''
ATSymbol: is an xqML Symbol of the type ``attribute''
APSymbol: is an xqML Symbol of the type ``attribute with predefined value''
VASymbol: is an xqML Symbol of the type ``attribute value''
ENSymbol: is an xqML Symbol of the type ``entity reference''
ElementsToClose: is an octet to be interpreted as an unsigned integer.

Xqueeze Association

Xqueeze uses an association between symbols and their corresponding XML identifiers and types as defined in a specification (DTD/Schema). This enables representation of known identifiers in the markup with symbols. Associating the type of an identifier along with it's name also makes it easy to various structural units of the document without having to use too many special characters and character-combinations.

Xqueeze Association algorithm (0.1.0)

This is the allgorithm that is used to map the identifiers found in a DTD/Schema to xqML Symbols. The steps of the algorithm are:

collect all Element identifiers together, discarding duplicates
collect all Empty Element identifiers together, discarding duplicates
collect all Attribute identifiers together, discarding duplicates
collect all identifiers together for Attributes that have predefined values, discarding duplicates
collect all Attribute Value identifiers together, discarding duplicates
collect all Entity References together, discarding duplicates
sort the above collections alphabetically and incrementally assign them symbols in the order enumerated in steps 1 to 6

This simple algorithm assures that the assignments would remain the same even if a particular specification (DTD/Schema) has slight variations in the way it's written in the generator's and consumer's copies, as long as both define the same things.

Xqueeze Association format (0.1.0)

Xqueeze associations are represented in a format that itself is quite compact and uses xqML Symbols themselves. The specification begins with an optional prolog that begins with the sequence <{0x02}. The prolog continues upto the next occurence of <. It is followed by sections that are denoted by <, followed by an xqML Symbol. The symbols for various sections are:

0x04: Elements
0x06: Empty Elements
0x08: Attributes
0x0A: Attributes with predefined values
0x0C: Attribute values
0x0E: Entity References

Within each section, individual entries are listed as <, followed by the a symbol, followed by the string that the symbol corresponds to. Thus the type of a symbol is determined by the section it is present in. A single association specification may have multiple sections of the same type and the ordering is not restricted. However, sections can't be nested.

The end of specifications is denoted by the sequence <{0x10}. This structure enables inline specification of the symbols associations, if required by a document.

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