 | Level: Intermediate Contributors: W3C 06 Feb 2007
Updated 25 Apr 2007 Canonical XML lets you create a physical representation of
an XML document that allows for the variations in XML syntax without
changing the meaning. Discover more about this standard method, which is
useful for testing and digital signatures, among other things.
Canonical XML Version
1.0
[W3C Recommendation] is a standard method for generating a
physical representation of an XML document, called the canonical
form, that accounts for the variations allowed in XML syntax without
changing meaning. For example, attribute order in XML is insignificant,
so if one document has all its attributes sorted in alphabetical order
and another is the same except that its attributes are sorted in some
different way, then both documents are identical as far as XML 1.0 is
concerned, despite the difference in the physical representation. This
presents some practical problems. For example, say you want to have a
digitally encrypted signature of a document to ensure that it isn't
tampered with. A rearrangement of the attributes would break the
signature, even though as far as XML standards are concerned, the
document has not really changed. The solution is to convert documents to
canonical form (a process called "canonicalization (c14n)") before
signature, text comparison, or any other such operation. This ensures
that changes insignificant in XML will be correctly accommodated. Work
has begun on
Canonical XML
1.1
[in development], which addresses several important problems
with the 1.0 specification.
Sometimes the XML that needs to be compared or signed is actually
just a portion of a bigger document. Even then, c14n generally must
account for the entire source document in order to handle details such
as namespace declarations. If you require c14n to be strictly limited to
a document subset, then you must use the related algorithm
Exclusive XML Canonicalization
Version 1.0
[W3C Recommendation].
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