Note

Date: Mar. 7, 1999
Link: http://www.w3.org/TR/NOTE-xml-canonical-req
Source Author or Organization: W3C

Excerpt from "Introduction": "The XML 1.0 Recommendation [XML] describes the syntax of a class of data objects called XML documents. It is possible, however, for logically equivalent XML documents to differ in their physical representation. In particular, two equivalent XML documents may differ on such issues as physical (ie entity) structure, attribute ordering, character encoding and insignificant whitespace. This means that equivalence testing cannot be done at the byte level for arbitrary XML documents. Such equivalence testing is useful in a number of domains including digital signatures, checksums, version control and conformance testing."

"Work has started elsewhere on the broader question of digital signatures in XML [IOTP-DSig, Brown-XML-DSig, DOMHASH]. The W3C has a forthcoming workshop on signed XML [DS-XML]."

"The Canonical XML specification aims to introduce a notion of equivalence between XML documents which can be tested at the syntactic level and, in particular, by byte-for-byte comparison. It shall describe the canonicalization of XML documents such that logically equivalent documents will have the same byte-for-byte representation. This form is referred to as the canonical form of the document."