< draft-wilde-xml-patch-01.txt   draft-wilde-xml-patch-02.txt >
Network Working Group E. Wilde Network Working Group E. Wilde
Internet-Draft EMC Internet-Draft EMC
Intended status: Standards Track January 16, 2013 Intended status: Standards Track February 8, 2013
Expires: July 20, 2013 Expires: August 12, 2013
A Media Type for XML Patch Operations A Media Type for XML Patch Operations
draft-wilde-xml-patch-01 draft-wilde-xml-patch-02
Abstract Abstract
The XML Patch media type "application/xml-patch+xml" defines an XML The XML Patch media type "application/xml-patch+xml" defines an XML
document structure for expressing a sequence of patch operations that document structure for expressing a sequence of patch operations that
are applied to an XML document. The XML Patch document format's are applied to an XML document. The XML Patch document format's
foundations are defined in RFC 5261, this specification defines a foundations are defined in RFC 5261, this specification defines a
document format and a media type registration, so that XML Patch document format and a media type registration, so that XML Patch
documents can be labeled with a media type, for example in HTTP documents can be labeled with a media type, for example in HTTP
conversations. conversations.
Note to Readers Note to Readers
This draft should be discussed on the apps-discuss mailing list [8]. This draft should be discussed on the apps-discuss mailing list [13].
Online access to all versions and files is available at github [9]. Online access to all versions and files is available at github [14].
Status of this Memo Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 20, 2013. This Internet-Draft will expire on August 12, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3 2. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3
3. Patch Document Format . . . . . . . . . . . . . . . . . . . . 4 3. Patch Document Format . . . . . . . . . . . . . . . . . . . . 4
4. Patch Examples . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Patch Examples . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6 5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 6 6. Implementation Hints . . . . . . . . . . . . . . . . . . . . . 6
6.1. From -00 to -01 . . . . . . . . . . . . . . . . . . . . . 6 6.1. Namespace Matching Rules . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 6.2. Patching Namespaces . . . . . . . . . . . . . . . . . . . 7
7.1. Normative References . . . . . . . . . . . . . . . . . . . 6 7. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.2. Informative References . . . . . . . . . . . . . . . . . . 7 7.1. From -01 to -02 . . . . . . . . . . . . . . . . . . . . . 9
Appendix A. XSD from RFC 5261 . . . . . . . . . . . . . . . . . . 7 7.2. From -00 to -01 . . . . . . . . . . . . . . . . . . . . . 9
Appendix B. ABNF for RFC 5261 . . . . . . . . . . . . . . . . . . 9 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10 8.1. Normative References . . . . . . . . . . . . . . . . . . . 9
8.2. Non-Normative References . . . . . . . . . . . . . . . . . 9
Appendix A. XSD from RFC 5261 . . . . . . . . . . . . . . . . . . 10
Appendix B. ABNF for RFC 5261 . . . . . . . . . . . . . . . . . . 12
Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 13
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction 1. Introduction
The Extensible Markup Language (XML) [1] is a common format for the The Extensible Markup Language (XML) [1] is a common format for the
exchange and storage of structured data. HTTP PATCH [6] extends HTTP exchange and storage of structured data. HTTP PATCH [6] extends HTTP
[7] with a method to perform partial modifications to resources. [7] with a method to perform partial modifications to resources.
HTTP PATCH requires that patch documents are being sent along with HTTP PATCH requires that patch documents are being sent along with
the request, and it is therefore useful if there are standardized the request, and it is therefore useful if there are standardized
patch document formats (identified by media types) for popular media patch document formats (identified by media types) for popular media
types. types.
skipping to change at page 3, line 26 skipping to change at page 3, line 26
document structure for expressing a sequence of operations to apply document structure for expressing a sequence of operations to apply
to a target XML document, suitable for use with the HTTP PATCH to a target XML document, suitable for use with the HTTP PATCH
method. Servers can freely choose which patch formats they want to method. Servers can freely choose which patch formats they want to
accept, and "application/xml-patch+xml" could be a simple default accept, and "application/xml-patch+xml" could be a simple default
format that can be used unless a server decides to use a different format that can be used unless a server decides to use a different
(maybe more sophisticated) patch format for XML. (maybe more sophisticated) patch format for XML.
The format for patch documents is based on the XML Patch Framework The format for patch documents is based on the XML Patch Framework
defined in RFC 5261 [2]. While RFC 5261 does define a concrete defined in RFC 5261 [2]. While RFC 5261 does define a concrete
syntax as well as the media type "application/patch-ops-error+xml" syntax as well as the media type "application/patch-ops-error+xml"
for error documents, it only defines XSD types for patch operations, for error documents, it only defines XML Schema (XSD) [8] types for
and thus the concrete document format and the media type for patch patch operations, and thus the concrete document format and the media
operations are defined in an XSD defined in this specification. type for patch operations are defined in an XSD defined in this
specification.
2. IANA Considerations 2. IANA Considerations
The Internet media type [3] for an XML Patch Document is application/ The Internet media type [3] for an XML Patch Document is application/
xml-patch+xml. xml-patch+xml.
Type name: application Type name: application
Subtype name: xml-patch+xml Subtype name: xml-patch+xml
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Restrictions on usage: none Restrictions on usage: none
Author: Erik Wilde <erik.wilde@emc.com> Author: Erik Wilde <erik.wilde@emc.com>
Change controller: IETF Change controller: IETF
3. Patch Document Format 3. Patch Document Format
The XML patch document format is based on a simple schema that uses a The XML patch document format is based on a simple schema that uses a
"patch" element as the document element, and allows a arbitrary "patch" element as the document element, and allows an arbitrary
sequence of "add", "remove", and "replace" elements as the children sequence of "add", "remove", and "replace" elements as the children
of the document element. These children follow the semantics defined of the document element. These children follow the semantics defined
in RFC 5261, which means that each element is treated as an in RFC 5261, which means that each element is treated as an
individual patch operation, and the result of each patch operation is individual patch operation, and the result of each patch operation is
a patched XML document that is the target XML document for the next a patched XML document that is the target XML document for the next
patch operation. patch operation.
The following example patch document uses the example from RFC 5261, The following example patch document uses the example from RFC 5261,
and simply uses a "patch" element and a new XML namespace. It shows and simply uses a "patch" element and a new XML namespace. It shows
the general structure of an XML patch document, as well as an example the general structure of an XML patch document, as well as an example
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<p:remove sel="*/elem[@a='bar']/y:child" ws="both"/> <p:remove sel="*/elem[@a='bar']/y:child" ws="both"/>
<p:add sel="*/elem[@a='bar']" type="@b">new attr</p:add> <p:add sel="*/elem[@a='bar']" type="@b">new attr</p:add>
</p:patch> </p:patch>
As this example demonstrates, both the document element "patch" and As this example demonstrates, both the document element "patch" and
the patch operation elements are in the same XML namespace. This is the patch operation elements are in the same XML namespace. This is
the result of RFC 5261 only defining types for the patch operation the result of RFC 5261 only defining types for the patch operation
elements, which then can be reused in schemas to define concrete elements, which then can be reused in schemas to define concrete
patch elements. patch elements.
RFC 5261 defines an XML Schema (XSD) for the patch operation types, RFC 5261 defines an XML Schema (XSD) [8] for the patch operation
which is included for reference in Appendix A. The normative version types, which is included for reference in Appendix A. The normative
of this schema is the one given in RFC 5261. The following schema version of this schema is the one given in RFC 5261. The following
for the XML Patch media type is based on the types defined in RFC schema for the XML Patch media type is based on the types defined in
5261, which are imported as "rfc5261.xsd" in the following schema. RFC 5261, which are imported as "rfc5261.xsd" in the following
The schema defines a "patch" document element, and then allows an schema. The schema defines a "patch" document element, and then
unlimited (and possible empty) sequence of the "add", "remove", and allows an unlimited (and possibly empty) sequence of the "add",
"replace" operation elements, which are directly based on the "remove", and "replace" operation elements, which are directly based
respective types from the schema defined in RFC 5261. on the respective types from the schema defined in RFC 5261.
<xs:schema targetNamespace="urn:ietf:rfc:XXXX" <xs:schema targetNamespace="urn:ietf:rfc:XXXX"
xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified"> xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified">
<xs:import schemaLocation="rfc5261.xsd"/> <xs:import schemaLocation="rfc5261.xsd"/>
<xs:element name="patch"> <xs:element name="patch">
<xs:complexType> <xs:complexType>
<xs:choice minOccurs="0" maxOccurs="unbounded"> <xs:choice minOccurs="0" maxOccurs="unbounded">
<xs:element name="add" type="add"/> <xs:element name="add" type="add"/>
<xs:element name="remove" type="remove"/> <xs:element name="remove" type="remove"/>
<xs:element name="replace" type="replace"/> <xs:element name="replace" type="replace"/>
</xs:choice> </xs:choice>
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5261, please refer to the numerous examples in that specification for 5261, please refer to the numerous examples in that specification for
concrete XML patch document examples. Most importantly, the examples concrete XML patch document examples. Most importantly, the examples
in RFC 5261 can be taken literally as examples for the XML Patch in RFC 5261 can be taken literally as examples for the XML Patch
media type, as long as it is assumed that the XML namespace for the media type, as long as it is assumed that the XML namespace for the
operation elements in these examples is the URI "urn:ietf:rfc:XXXX". operation elements in these examples is the URI "urn:ietf:rfc:XXXX".
5. Security Considerations 5. Security Considerations
... ...
6. Change Log 6. Implementation Hints
This section is informative. It described some issues that might be
interesting for implementors, but it might also be interesting for
users of XML Patch that want to understand some of the differences
between standard XPath 1.0 processing, and the processing model of
RFC 5261.
6.1. Namespace Matching Rules
RFC 5261 defines standard rules for matching prefixed names in
expressions: Any prefixes are interpreted according to the namespace
bindings of the diff document (the document that the expression is
applied against). This means that each prefixed name can be
interpreted in the context of the diff document.
For unprefixed names in expressions, the rules depart from XPath 1.0
[9]. XPath 1.0 defines that unprefixed names in expressions match
namespace-less names (i.e., there is no "default namespace" for names
used in XPath 1.0 expressions). RFC 5261 requires, however, that
unprefixed names in expressions must use the default namespace of the
diff document (if there is one). This means that it is not possible
to simply take a selector from a patch document and evaluate it in
the context of the diff document according to the rules of XPath 1.0,
because this would interpret unprefixed names incorrectly. As a
consequence, it is not possible to simply take an XPath 1.0 processor
and evaluate XMPL Patch selectors in the context of the diff
document.
As an extension of XPath 1.0's simple model, XPath 2.0 [10] specifies
different processing rules for unprefixed names: They are matched
against the URI of the "default element/type namespace", which is
defined as part of an expression's static context. In some XPath 2.0
applications this can be set; XSLT 2.0 for example has the ability to
define an "xpath-default-namespace", which then will be used to match
unprefixed names in expressions. Thus, by using an XPath 2.0
implementation that allows to set this URI, and setting it to the
default namespace of the diff document (or leaving it undefined if
there is no such default namespace), it is possible to use an out-of-
the-box XPath 2.0 implementation for evaluating XML Patch selectors.
Please keep in mind, however, that evaluating selectors is only one
part of applying patches. When it comes to applying the actual patch
operations, neither XPath 1.0 nor XPath 2.0 are sufficient, because
they are not preserving some of the information from the XML syntax
(specifically: namespace declarations) that is required to correctly
apply patch operations. The following section described this issue
in more detail.
[[[ Currently, RFC 5261's section on namespace matching explains
XPath 2.0's rules incorrectly
<http://tools.ietf.org/html/rfc5261#section-4.2.2>. An erratum has
been filed
<http://www.rfc-editor.org/errata_search.php?rfc=5261&eid=3477>
which, upon verification, will be linked to from here. ]]]
6.2. Patching Namespaces
One of the issues when patching namespaces based on XPath is that
XPath exposes namespaces different than the XML 1.0 [11] syntax for
XML Namespaces [12]. In the XML syntax, a namespace is declared with
an attribute using the reserved name or prefix "xmlns", and this
results in this namespace being available recursively through the
document tree. In XPath, the namespace declaration is not exposed as
an attribute (i.e., the attribute, although syntactically an XML
attribute, is not accessible in XPath), but the namespace nodes are
exposed recursively through the tree.
RFC 5261 uses the terms "namespace declaration" and "namespace"
almost interchangeably, but it is important to keep in mind that the
namespace declaration is an XML syntax construct that is unavailable
in XPath, while the namespace itself is a logical construct that is
not visible in the XML syntax, but a result of a namespace
declaration. The intent of RFC 5261 is to patch namespaces as if
namespace declarations were patched, and thus it only allows to patch
namespace nodes on the element nodes where the namespace has been
declared.
Patching namespaces in XML Patch is supposed to "emulate" the effect
of actually changing the namespace declaration (which is why a
namespace can only be patched at the element where it has been
declared). Therefore, when patching a namespace, even though XPath's
"namespace" axis is used, implementations have to make sure that not
only the one selected namespace node is being patched, but that all
namespaces nodes resulting from the namespace declaration of this
namespace are patched accordingly.
This means that an implementation might have to descend into the
tree, matching all namespace nodes with the selected prefix/URI pair
recursively, until it encounters namespace declarations with the same
prefix it is patching. Determining this requires access to the diff
document beyond XPath, because in XPath itself namespace declarations
are not represented, and thus such a recursive algorithm wouldn't
know when to stop. Consider the following document:
<x xmlns:a="tag:42">
<y xmlns:a="tag:42"/>
</x>
If this document is patched with a selector of /x/namespace::a, then
only the namespace node on element x should be patched, even though
the namespace node on element y has the same prefix/URI combination
than the one on element x. Determining that the repeated namespace
declaration was present at all on element y is impossible when using
XPath alone, so implementations must have an alternative way to
determine the difference between the document above, and this one:
<x xmlns:a="tag:42">
<y/>
</x>
In this second example, patching with a selector of /x/namespace::a
should indeed change the namespace nodes on elements x and y, because
they both have been derived from the same namespace declaration.
The conclusion of these considerations is that for implementing XML
Patch, access to the XML syntax (specifically: namespace
declarations) is necessary. As a result, implementations attempting
to exclusively use the XPath model for implementing XML Patch will
fail to correctly address certain edge cases (as the one shown
above).
[[[ Currently, RFC 5261's section on replacing namespaces mixes the
terms "namespace declaration" and "namespace"
<http://tools.ietf.org/html/rfc5261#section-4.4.3>. An erratum has
been filed <http://www.rfc-editor.org/errata_search.php?eid=3478>
which, upon verification, will be linked to from here. ]]]
7. Change Log
Note to RFC Editor: Please remove this section before publication. Note to RFC Editor: Please remove this section before publication.
6.1. From -00 to -01 7.1. From -01 to -02
o Textual edits.
o Added section on "Implementation Hints" (Section 6).
7.2. From -00 to -01
o Removed Mark Nottingham from author list. o Removed Mark Nottingham from author list.
o Changed media type name to application/xml-patch+xml (added suffix o Changed media type name to application/xml-patch+xml (added suffix
per draft-ietf-appsawg-media-type-suffix-regs) per draft-ietf-appsawg-media-type-suffix-regs)
o Added ABNF grammar derived from XSD (Appendix B) o Added ABNF grammar derived from XSD (Appendix B)
7. References 8. References
7.1. Normative References 8.1. Normative References
[1] Murata, M., St. Laurent, S., and D. Kohn, "XML Media Types", [1] Murata, M., St. Laurent, S., and D. Kohn, "XML Media Types",
RFC 3023, January 2001. RFC 3023, January 2001.
[2] Urpalainen, J., "An Extensible Markup Language (XML) Patch [2] Urpalainen, J., "An Extensible Markup Language (XML) Patch
Operations Framework Utilizing XML Path Language (XPath) Operations Framework Utilizing XML Path Language (XPath)
Selectors", RFC 5261, September 2008. Selectors", RFC 5261, September 2008.
[3] Freed, N. and J. Klensin, "Media Type Specifications and [3] Freed, N., Klensin, J., and T. Hansen, "Media Type
Registration Procedures", BCP 13, RFC 4288, December 2005. Specifications and Registration Procedures", BCP 13, RFC 6838,
January 2013.
[4] Freed, N. and N. Borenstein, "Multipurpose Internet Mail [4] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Bodies", Extensions (MIME) Part One: Format of Internet Message Bodies",
RFC 2045, November 1996. RFC 2045, November 1996.
[5] Freed, N. and N. Borenstein, "Multipurpose Internet Mail [5] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046, Extensions (MIME) Part Two: Media Types", RFC 2046,
November 1996. November 1996.
7.2. Informative References 8.2. Non-Normative References
[6] Dusseault, L. and J. Snell, "PATCH Method for HTTP", RFC 5789, [6] Dusseault, L. and J. Snell, "PATCH Method for HTTP", RFC 5789,
March 2010. March 2010.
[7] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., [7] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol -- Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol --
HTTP/1.1", RFC 2616, June 1999. HTTP/1.1", RFC 2616, June 1999.
[8] Thompson, H., Beech, D., Maloney, M., and N. Mendelsohn, "XML
Schema Part 1: Structures Second Edition", World Wide Web
Consortium Recommendation REC-xmlschema-1-20041028,
October 2004,
<http://www.w3.org/TR/2004/REC-xmlschema-1-20041028>.
[9] DeRose, S. and J. Clark, "XML Path Language (XPath) Version
1.0", World Wide Web Consortium Recommendation REC-xpath-
19991116, November 1999,
<http://www.w3.org/TR/1999/REC-xpath-19991116>.
[10] Boag, S., Berglund, A., Kay, M., Simeon, J., Robie, J.,
Chamberlin, D., and M. Fernandez, "XML Path Language (XPath)
2.0 (Second Edition)", World Wide Web Consortium
Recommendation REC-xpath20-20101214, December 2010,
<http://www.w3.org/TR/2010/REC-xpath20-20101214>.
[11] Sperberg-McQueen, C., Yergeau, F., Paoli, J., Maler, E., and T.
Bray, "Extensible Markup Language (XML) 1.0 (Fifth Edition)",
World Wide Web Consortium Recommendation REC-xml-20081126,
November 2008, <http://www.w3.org/TR/2008/REC-xml-20081126>.
[12] Hollander, D., Layman, A., Bray, T., Tobin, R., and H.
Thompson, "Namespaces in XML 1.0 (Third Edition)", World Wide
Web Consortium Recommendation REC-xml-names-20091208,
December 2009,
<http://www.w3.org/TR/2009/REC-xml-names-20091208>.
URIs URIs
[8] <https://www.ietf.org/mailman/listinfo/apps-discuss> [13] <https://www.ietf.org/mailman/listinfo/apps-discuss>
[9] <https://github.com/dret/I-D/tree/master/xml-patch> [14] <https://github.com/dret/I-D/tree/master/xml-patch>
Appendix A. XSD from RFC 5261 Appendix A. XSD from RFC 5261
For reference, this section contains a copy of the XSD defining the For reference, this section contains a copy of the XML Schema (XSD)
add, replace, and remove types in RFC 5261 [2]. This section is [8] defining the add, replace, and remove types in RFC 5261 [2].
informational only, and the definitive version of the schema is the This section is informational only, and the definitive version of the
one listed in RFC 5261. schema is the one listed in RFC 5261.
<?xml version="1.0" encoding="UTF-8"?> <?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE schema [ <!DOCTYPE schema [
<!ENTITY ncname "\i\c*"> <!ENTITY ncname "\i\c*">
<!ENTITY qname "(&ncname;:)?&ncname;"> <!ENTITY qname "(&ncname;:)?&ncname;">
<!ENTITY aname "@&qname;"> <!ENTITY aname "@&qname;">
<!ENTITY pos "\[\d+\]"> <!ENTITY pos "\[\d+\]">
<!ENTITY attr "\[&aname;='(.)*'\]|\[&aname;=&quot;(.)*&quot;\]"> <!ENTITY attr "\[&aname;='(.)*'\]|\[&aname;=&quot;(.)*&quot;\]">
<!ENTITY valueq "\[(&qname;|\.)=&quot;(.)*&quot;\]"> <!ENTITY valueq "\[(&qname;|\.)=&quot;(.)*&quot;\]">
<!ENTITY value "\[(&qname;|\.)='(.)*'\]|&valueq;"> <!ENTITY value "\[(&qname;|\.)='(.)*'\]|&valueq;">
<!ENTITY cond "&attr;|&value;|&pos;"> <!ENTITY cond "&attr;|&value;|&pos;">
skipping to change at page 10, line 26 skipping to change at page 13, line 30
id = ( "id(" [ "'" ncname "'" ] ")" ) / ( "id(" [ DQUOTE ncname DQUOTE ] ")" ) id = ( "id(" [ "'" ncname "'" ] ")" ) / ( "id(" [ DQUOTE ncname DQUOTE ] ")" )
com = "comment()" com = "comment()"
text = "text()" text = "text()"
nspa = "namespace::" ncname nspa = "namespace::" ncname
cnodes = ( text / com / pi ) [ pos ] cnodes = ( text / com / pi ) [ pos ]
child = cnodes / step child = cnodes / step
last = child / aname / nspa last = child / aname / nspa
xpath = [ "/" ] ( ( id [ 0*( "/" step ) "/" last ] ) / ( 0*( step "/" ) last ) ) xpath = [ "/" ] ( ( id [ 0*( "/" step ) "/" last ] ) / ( 0*( step "/" ) last ) )
xpath-add = [ "/" ] ( ( id [ 0*( "/" step ) "/" child ] ) / ( 0*( step "/" ) child ) ) xpath-add = [ "/" ] ( ( id [ 0*( "/" step ) "/" child ] ) / ( 0*( step "/" ) child ) )
Appendix C. Acknowledgements
Thanks for comments and suggestions provided by Bas de Bakker.
Author's Address Author's Address
Erik Wilde Erik Wilde
EMC EMC
Email: erik.wilde@emc.com Email: erik.wilde@emc.com
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