DRAFT 1 +
As with many sorts of structured information, there are many +categories of information that may be deemed "important" for +some task. Canonical forms are standard ways to represent +such classes of information. For testing XML, and potentially +for other purposes, three XML Canonical Forms have +been defined as of this writing:
For a document already in a given canonical form, recanonicalizing +to that same form will change nothing. Canonicalizing second or +third forms to the first canonical form discards all declarations. +Canonicalizing second or third forms to the other form has no effect. + +
The author is pleased to acknowledge help from
+James Clark in defining the additional canonical forms.
+
+
+
+First XML Canonical Form
+
+
+
This description has been extracted from the version at + +http://www.jclark.com/xml/canonxml.html. + +
+Every well-formed XML document has a unique structurally equivalent +canonical XML document. Two structurally equivalent XML +documents have a byte-for-byte identical canonical XML document. +Canonicalizing an XML document requires only information that an XML +processor is required to make available to an application. +
+A canonical XML document conforms to the following grammar: +
+CanonXML ::= Pi* element Pi*
+element ::= Stag (Datachar | Pi | element)* Etag
+Stag ::= '<' Name Atts '>'
+Etag ::= '</' Name '>'
+Pi ::= '<?' Name ' ' (((Char - S) Char*)? - (Char* '?>' Char*)) '?>'
+Atts ::= (' ' Name '=' '"' Datachar* '"')*
+Datachar ::= '&' | '<' | '>' | '"'
+ | '	'| ' '| ' '
+ | (Char - ('&' | '<' | '>' | '"' | #x9 | #xA | #xD))
+Name ::= (see XML spec)
+Char ::= (see XML spec)
+S ::= (see XML spec)
+
++Attributes are in lexicographical order (in Unicode bit order). +
+A canonical XML document is encoded in UTF-8. +
+Ignorable white space is considered significant and is treated equivalently
+to data.
+
+
+
+Second XML Canonical Form
+
+
Modified to ensure that literals are surrounded by single quotes. +
This canonical form is identical to the first form, with +one significant addition. All XML processors are required to +report the name and external identifiers of notations that +are declared and referred to in an XML document (section 4.7); +those reports are reflected in declarations in this form, +presented in lexicographic order. + +
Note that all public identifiers must be normalized before being +presented to applications (section 4.2.2). + +
System identifiers are normalized on output to be relative +to the input document, if that is possible, with the shortest +such relative URI. All other URIs must be absolute. Any +hash mark and fragment ID, if erroneously present on input, are +removed. Any non-ASCII characters in the URI must be escaped +as specified in the XML specification (section 4.2.2). + +
+CanonXML2 ::= DTD2? CanonXML
+DTD2 ::= '<!DOCTYPE ' name ' [' #xA Notations? ']>' #xA
+Notations ::= ( '<!NOTATION ' Name '
+ (('PUBLIC ' PubidLiteral ' ' SystemLiteral)
+ |('PUBLIC ' PubidLiteral)
+ |('SYSTEM ' SystemLiteral))
+ '>' #xA )*
+PubidLiteral ::= "'" PubidChar* "'"
+SystemLiteral ::= "'" [^']* "'"
+
+
+
+ The requirement of this canonical form differs slightly from that
+of the XML specification itself in that all declared notations
+must be listed, not just those which were referred to.
+Should that change? SAX supports it easily.
+
+
+
+Third XML Canonical Form
+
+
This canonical form is identical to the second form, with +two significant exceptions reflecting requirements placed on +validating XML processors:
This builds on the grammar productions included above. + +
+CanonXML3 ::= DTD3? CanonXML
+DTD3 ::= '<!DOCTYPE ' name ' [' #xA Notations? Unparsed? ']>' #xA
+Unparsed ::= ( '<!ENTITY ' Name '
+ (('PUBLIC ' PubidLiteral ' ' SystemLiteral)
+ |('SYSTEM ' SystemLiteral))
+ 'NDATA ' Name
+ '>' #xA )*
+
+
+The requirement of this canonical form differs slightly from that +of the XML specification itself in that all declared unparsed entities +must be listed, not just those which were referred to. +Should that change? SAX supports it easily. + +
+
+xml-feedback@java.sun.com + + + +