SIMPLE WG                                                  J. Urpalainen
Internet-Draft                                     Nokia Research Center
Expires: September 7, 2006                                 March 6, 2006


An Extensible Markup Language (XML) Patch Operations Framework Utilizing
                  XML Path Language (XPath) Selectors
                   draft-ietf-simple-xml-patch-ops-02

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Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   Extensible Markup Language (XML) documents are widely used as
   containers for the exchange and storage of arbitrary data in today's
   systems.  Updates to this data require transporting of the entire XML
   document between hosts, unless there's a mechanism that allows
   exchanging only the updates of XML documents.  This document
   describes an XML patch framework utilizing XML Path language (XPath)
   selectors.  These selector values and updated new data content
   constitute the basis of patch operations described in this document.



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   In addition to them, with basic <add>, <replace> and <remove>
   directives a set of patches can then be applied to update an existing
   XML document.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Basic Features and Requirements  . . . . . . . . . . . . . . .  4
   4.  Patch Operations . . . . . . . . . . . . . . . . . . . . . . .  6
     4.1.  Locating the Target for a Patch  . . . . . . . . . . . . .  6
     4.2.  Namespace Mangling . . . . . . . . . . . . . . . . . . . .  6
     4.3.  <add> Element  . . . . . . . . . . . . . . . . . . . . . .  8
     4.4.  <replace> Element  . . . . . . . . . . . . . . . . . . . . 11
     4.5.  <remove> Element . . . . . . . . . . . . . . . . . . . . . 12
   5.  Error Handling . . . . . . . . . . . . . . . . . . . . . . . . 14
   6.  Usage of Patch Operations  . . . . . . . . . . . . . . . . . . 14
   7.  Usage of Selector Values . . . . . . . . . . . . . . . . . . . 14
   8.  Full Example . . . . . . . . . . . . . . . . . . . . . . . . . 14
   9.  XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . . 16
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 18
     10.1. XML Schema Registration  . . . . . . . . . . . . . . . . . 18
   11. Security Considerations  . . . . . . . . . . . . . . . . . . . 18
   12. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 19
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 19
     13.2. Informative References . . . . . . . . . . . . . . . . . . 20
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 21
   Intellectual Property and Copyright Statements . . . . . . . . . . 22





















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1.  Introduction

   Extensible Markup Language (XML) [2] documents are widely used as
   containers for the exchange and storage of arbitrary data in today's
   systems.  An example of such a system is the Common Presence Profile
   (CPP) [16] compatible presence system, in which presence data is
   represented using the XML based Presence Information Data Format
   (PIDF) [17].  Updates to this data require transporting of the entire
   XML document between hosts, unless there's a mechanism that allows
   exchanging only the updates of an XML document.

   This document describes an XML patch framework which utilizes XML
   Path language (XPath) [3] selectors.  An XPath selector is used to
   pinpoint the target for a change.  These selector values and updated
   new data content constitute the basis of patch operations described
   in this document.  In addition to them, with basic <add>, <replace>
   and <remove> directives a set of patches can be applied to update an
   existing initial XML document.  With these patch operations, a simple
   semantics for data oriented XML documents [7] is achieved, that is,
   modifications like additions, removals or substitutions of elements
   and attributes can easily be performed.  This document does not
   describe a full XML diff format, only basic patch operation elements
   which can be embedded within a full format.

   As an example, in the Session Initiation Protocol (SIP) [18] based
   presence system a partial PIDF XML document format [13] consists of
   the existing PIDF document format combined with the patch operations
   elements described in this document.  In general, patch operations
   can be used in any application that exchanges XML documents, for
   example within the SIP Events framework [12].  Another example is
   XCAP-diff [14] which uses this framework for sending partial updates
   of changes to XCAP [15] resources.


2.  Conventions

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
   and "OPTIONAL" are to be interpreted as described in RFC 2119, BCP 14
   [1] and indicate requirement levels for compliant implementations.

   The following terms are used in this document:

   Initial XML document: An initial XML document that is going to be
      updated with a set of patches.






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   XML diff document: A frame XML document that contains patch operation
      elements, namespace declarations and all the document content
      changes that are needed in order to transform an initial XML
      document into a new patched XML document.

   Patched XML document: An XML document that results after applying one
      or more patch operations defined in the XML diff document to the
      initial XML document.

   Patch operation: A single change, i.e. a patch that is being applied
      to update an initial XML document.

   Patch operation element: An XML element that represents a single
      patch operation.

   Type definition for an element: A W3C Schema type definition for an
      element that describes a patch operation content.

   In-scope namespace declaration: A list of all in-scope namespace
      declarations within a context node.  The QName expansion of a
      context node is based on mapping a prefix with one of these
      declarations.  For an element, one namespace binding may have an
      empty prefix.

   Positional constraint: A number enclosed with square brackets.  It
      can be used as a location step predicate.

   Located target node: A node which was found from the initial XML
      document with the aid of an XPath selector value.

   White space text node: A text node which contains only white space.


3.  Basic Features and Requirements

   In this framework, XPath selector values and new data content are
   embedded within XML elements, the names of which imply the type of a
   modification: <add>, <replace> or <remove>.  These elements, or
   synonymously patch operations as used in this document, are described
   by defining their schema types with the W3C Schema language [6].
   XPath selectors pinpoint the target for a change and they are
   expressed as attributes of these elements.  The child node(s) of
   patch operation elements contain the new data content.  In general
   when applicable, the new content SHOULD be moved unaltered to the
   patched XML document.

   The specifications utilizing these element types MUST define the full
   XML diff format with an appropriate MIME type [11] and a character



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   set, e.g.  UTF-8 [9].  The partial PIDF format [13] includes this
   schema and describes additional definitions to produce a complete XML
   diff format for partial presence information updates.

   As the schema defined in this document does not declare any target
   namespace, the type definitions inherit the target namespace of the
   including schema.  Therefore, additional namespace declarations
   within the XML diff documents can be avoided.

   It is anticipated that applications using these types will define
   <add>, <replace> and <remove> elements based on the corresponding
   type definitions in this schema.  In addition, an application may
   reference only a subset of these type definitions.  A future
   extension can introduce other operations, e.g. with document oriented
   models [7] a <move> operation and a text node patching algorithm
   combined with <move> would undoubtedly produce smaller XML diff
   documents.

   The instance document elements based on these schema type definitions
   MUST be well formed and SHOULD be valid.

   The following XPath 1.0 data model node types can be added, replaced
   or removed with this framework: elements, attributes, namespaces,
   comments, texts and processing instructions.  The full XML prolog
   including e.g.  XML entities [2] and the root node of an XML document
   cannot be patched according to this framework.  However, patching of
   comments and processing instructions of the root node is allowed.
   Naturally the removal or addition of a document root element is not
   allowed as any valid XML document MUST always contain a single root
   element.  Also note that support for external entities is beyond the
   scope of this framework.

      Note: Implementations must thus be based on XML parsers and XPath
      interpreters that support all XPath 1.0 data model node types
      except the root node of an XML document.  In addition to the
      location capability of these nodes, some application programming
      interfaces are needed for their manipulation in practice.

   XML documents which are equivalent for the purposes of many
   applications MAY differ in their physical representation.  The aim of
   this document is to describe a deterministic framework where the
   canonical form with comments [4] of an XML document determines
   logical equivalence.  For example, white space text nodes MUST be
   processed properly in order to fulfil this requirement as white space
   is by default significant [4].






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4.  Patch Operations

   An XML diff document contains a collection of patch operation
   elements, including one or more <add>, <replace> and <remove>
   elements.  These patch operations will be applied sequentially in the
   document order.  After the first patch has been applied to update an
   initial XML document, the patched XML document becomes a new initial
   XML document.  This procedure repeats until all patches have
   successfully been processed.  In other words, this framework does not
   allow "apply all occurrences" in one pass.

4.1.  Locating the Target for a Patch

   Each patch operation element contains a 'sel' attribute.  The value
   of this attribute is an XPath selector with a restricted subset of
   the full XPath 1.0 recommendation.  The 'sel' value is used to locate
   a single unique target node from the initial XML document.  This
   located node pinpoints the target for a change and usually it is an
   element, which is e.g. either updated itself or some child node(s)
   are added into it.  It may also be for instance a comment node, after
   which some other sibling node(s) are inserted.  In any case, it is an
   error condition if multiple nodes are found during the evaluation of
   this selector value.

   The XPath selections of the 'sel' attribute always start from the
   root node of a document.  Thus relative location paths SHOULD be used
   so that the starting root node selection "/" can be omitted.  When
   locating elements in a document tree, a node test can either be a "*"
   character or a QName.  A "*" character selects all element children
   of the context node.  Right after the node test, a location step can
   contain one or more predicates in any order.  An attribute value
   comparison is one of the most typical predicates.  The string value
   of the current context node or a child element may alternatively be
   used to identify elements in the tree.  The character ".", which
   denotes a current context node selection, is an abbreviated form of
   "self::node()".  Lastly, positional constraints like "[2]" can also
   be used as an additional predicate.

   An XPath 1.0 "id()" node-set function MAY also be used to identify
   unique elements from the document tree.  The schema that describes
   the content model of the document MUST then use an attribute with the
   type ID [7] or with non-validating XML parsers, an "xml:id" [8]
   attribute MUST have been used within an instance document.

4.2.  Namespace Mangling

   While the XPath recommendation specifies that prefixes can be used in
   location steps, it does not specify how associated namespace URIs are



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   discovered during these evaluations.  In the patch operation
   framework QName [5] expansion within a location step is evaluated
   according to the namespace declarations of the XML diff document.
   Thus the namespace URIs for these prefixes are found from the in-
   scope namespaces of the patch operation element.  In other words, the
   XML diff document contains all needed information for QName
   expansions in order to perform XPath searches from the initial XML
   document.

      Note: It should be emphasized that prefixes within the XPath
      selectors MAY be different than those of the initial XML document
      because the matching of nodes is based on expanded names, i.e. a
      prefix maps to a namespace URI and these URIs and local names MUST
      be identical.  For example, with a selector "p:foo", "p" maps to a
      namespace URI and "foo" is the local name.

   In this framework, when a node test is "foo" and the patch operation
   element has an in-scope default namespace declaration, a qualified
   <foo> element from the initial XML document is being searched.  That
   is, the namespace URI of the expanded name of the located <foo>
   element MUST then be identical compared to this default namespace
   declaration.  If there's not an in-scope default namespace
   declaration within the evaluation context, an unqualified <foo>
   element is located.

      Note: By contrast, in XPath 1.0 a "foo" selector always locates an
      unqualified <foo> element but in XPath 2.0 [10] also a qualified
      one which is attached with the default namespace declaration.

      Note: The XPath 1.0 recommendation specifies "namespace-uri()" and
      "local-name()" node-set functions which can be used within
      predicates.  These functions may be utilized during XPath
      evaluations if there are no other means to "register" prefixes
      with associated namespace URIs.  They can also be used when
      handling selections where default namespaces are attached to
      elements.  However, the schema type definitions for these patch
      operation elements do not allow the usage of these functions.

   Also elements within the changed data content are usually namespace
   qualified.  For example, when adding a new namespace qualified
   element to the initial XML document, the namespace declaration
   reference of this new element belongs first to the XML diff document.
   Naturally after copying or moving this element, the attached
   namespace MUST refer to a declaration within the patched XML
   document.  If this namespace is declared in the patch operation
   element or within its ascendants, these references MUST thus be
   changed.  Like in XPath, the mapping of these references is based on
   identical namespace URIs, not prefixes.  The namespace with an



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   identical URI from the in-scope namespaces of a context node of the
   initial XML document MUST be chosen.  However, if overlapping in-
   scope namespaces exist, i.e., there are several in-scope namespaces
   with an identical namespace URI, then the namespace with the same
   prefix MUST be chosen.  If an equivalent prefix is not then found, an
   error occurs.  For instance, this kind of overlapping can happen when
   a namespace qualified attribute is added while elements are attached
   with an identical default namespace declaration.

   When the new added or updated elements contain namespace
   declarations, the namespace nodes move unaltered from the XML diff
   document to the patched XML document.  Default namespace declarations
   can only be added by this way but prefixed namespace declarations MAY
   be added or removed with XPath namespace axis semantics shown later
   in this document.

      Note: In practice, this namespace mangling means that an XML diff
      document MUST only know the namespace URIs of qualified nodes, the
      prefixes of the initial XML document are not significant unless
      there are those overlapping namespace declarations.  In other
      words, regardless whether the prefixes of qualified elements of
      the initial XML document are empty (default namespace attached) or
      not, the XML diff document may remain the same.

4.3.  <add> Element

   The <add> element represents the addition of some new content to the
   initial XML document: e.g. a new element can be appended into an
   existing element.

   The new data content exists as the child node(s) of the <add>
   element.  When adding attributes and namespaces the child node of the
   <add> element MUST be a single text node.  Otherwise, the <add>
   element can contain any mixture of element, text, comment or
   processing instruction nodes in any order.  All children of the <add>
   element are then copied into an initial XML document.  The described
   namespace mangling procedure applies to added elements, which include
   all of their attribute, namespace and descendant nodes.

   The <add> element type has three attributes: 'sel', 'type' and 'pos'.

   The value of the optional 'type' attribute is only used when adding
   attributes and namespaces.  Then the located target node MUST be an
   element into which new attributes and namespace declarations are
   inserted.  When the value of this 'type' attribute equals "@attr" the
   purpose is to add a new attribute node with the name 'attr'.  The
   value of this new 'attr' attribute is the text node content of the
   <add> element.  The less frequently used, prefixed, i.e. namespace



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   qualified attributes can also be added.  If the value of the 'type'
   attribute equals "namespace::pref" the aim is to add a new "pref"
   prefixed namespace declaration and the text node content of the <add>
   element contains the corresponding namespace URI.

      Note: The 'type' attribute is thus also an XPath selector, but it
      only locates attributes and namespaces.  Attribute axis
      "attribute" has an abbreviated form "@" unlike the "namespace"
      axis which doesn't have an abbreviated form.  Double colons "::"
      are used as an axis separator in XPath.

   The value of the optional 'pos' attribute indicates the positioning
   of new data content.  It is not used when adding attributes or
   namespaces.  When neither 'type' nor 'pos' attribute exist, the
   children of the <add> element are then appended as the last child
   node(s) of the located target element.  When the value of 'pos'
   attribute is "prepend" the new node(s) are added as the first child
   node(s) of the located target element.  With the value of "before"
   the added new node(s) MUST be the immediate preceding sibling node(s)
   and with "after" the immediate following sibling node(s) of the
   located target node.

   Some examples follow where nodes are not namespace qualified and
   prefixes are therefore not used.  The whole XML diff content is not
   shown in these examples, only patch operation elements because of
   simplicity reasons:

   <add sel="doc"><foo id="ert4773">This is a new child</foo></add>

   Once the <doc> element has been found from the initial XML document,
   a new <foo> element is appended as the last child node of the <doc>
   element.  The located target node: the <doc> element is naturally the
   root element of the initial XML document.  The new <foo> element
   contains an 'id' attribute and a child text node.

   An example for an addition of an attribute:

   <add sel="doc/foo[@id='ert4773']" type="@user">Bob</add>

   This operation adds a new 'user' attribute to the <foo> element which
   was located by using an 'id' attribute value predicate.  The value of
   this new 'user' attribute is "Bob".

   A similar patched XML document is achieved when using a validating
   XML parser, if the 'sel' selector value had been 'id("ert4773")' and
   if the data type of the 'id' attribute is "ID" [7].





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      Note: As the 'sel' selector value MAY contain quotation marks,
      escaped forms: "&quot;" or "&apos;" can be used within attribute
      values.  However, it is often more appropriate to use the
      apostrophe (') character as shown in these examples.  An
      alternative is also to interchange the apostrophes and quotation
      marks.

   An example for an addition of a prefixed namespace declaration:

   <add sel="doc" type="namespace::pref">urn:ns:xxx</add>

   This operation adds a new namespace declaration to the <doc> element.
   The prefix of this new namespace node is thus "pref" and the
   namespace URI is "urn:ns:xxx".

   An example for an addition of a comment node:

   <add sel="doc/foo[@id='ert4773']" pos="before"><!-- comment --></add>

   This operation adds a new comment node just before the <foo> element
   as an immediate preceding sibling node.  This is also an example how
   a 'pos' attribute directive can be used.

   Some complexity arises when so called white space text nodes exist
   within an initial XML document.  The XPath 1.0 data model requires
   that a text node MUST not have another text node as an immediate
   sibling node.  For instance, if an add operation is like this:

   <add sel="doc">
     <foo id="ert4773">This is a new child</foo></add>

   The <add> element has then two child nodes: a white space text node
   (a linefeed and two spaces) and a <foo> element.  If the existing
   last child of the <doc> element is a text node, its content and the
   white space text node content MUST then be combined together.
   Otherwise (white space) text nodes can be added just like elements
   and thus, the canonical form of the patched XML document easily
   remains deterministic.  As several sibling nodes can be inserted with
   a single <add> operation, a "pretty printing" style can easily be
   maintained.

   Still another example about the handling of text nodes.  Consider
   this example:

   <add sel="*/foo/text()[2]" pos="after">new<bar/>elem</add>

   The second text node child of the <foo> element is first located.
   The added new content contains two text nodes and an element.  As



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   there can not be immediate sibling text nodes, the located target
   text node content and the first new text node content MUST be
   combined together.  In essence, if the 'pos' value had been "before",
   the second new text node content would effectively have been
   prepended to the located target text node.

      Note: It is still worth noting that text nodes MAY contain CDATA
      sections, the latter of which are not treated as separate nodes.
      Once these CDATA sections exist within the new text nodes, they
      SHOULD be moved unaltered to the patched XML document.

   While XML entities [2] cannot be patched with this framework, the
   references to other than predefined internal entities can exist
   within text nodes or attributes when the XML prolog contains those
   declarations.  These references may then be preserved if both the XML
   diff and the initial XML document have identical declarations within
   their prologs.  Otherwise, references may be replaced with identical
   text as long as the "canonically equivalent" rule is obeyed.

4.4.  <replace> Element

   The <replace> element represents a replacement operation: e.g. an
   existing element is updated with a new element or an attribute value
   is replaced with a new value.  This <replace> operation always
   updates a single node or node content at a time.

   The <replace> element type has only a 'sel' attribute.  If the
   located target node is an element, a comment or a processing
   instruction, then the child of the <replace> element MUST also be of
   the same type.  Otherwise the <replace> element MUST have text
   content or it MAY be empty when replacing an attribute value or a
   text node content.

   Examples for replace operations, first a replacement of an element:

   <replace sel="doc/foo[@a='1']"><bar a="2"/></replace>

   This will update the <foo> element which has an 'a' attribute with
   value "1".  The located target element is replaced with the <bar>
   element.  So all descendant nodes, namespace declarations and
   attributes of the replaced <foo> element, if any existed, are thus
   removed.

   An example for a replacement of an attribute value:

   <replace sel="doc/@a">new value</replace>

   This will replace the 'a' attribute content of the <doc> element with



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   the value "new value".  If the <replace> element is empty, the 'a'
   attribute MUST then remain in the patched XML document appearing like
   <doc a=""/>.

   An example for a replacement of a namespace URI:

   <replace sel="doc/namespace::pref">urn:new:xxx</replace>

   This will replace the URI value of 'pref' prefixed namespace node
   with "urn:new:xxx".  The parent node of the namespace declaration
   MUST be the <doc> element, otherwise an error occurs.

   An example for a replacement of a comment node:

   <replace sel="doc/comment()[1]"><!-- This is the new content
   --></replace>

   This will replace a comment node.  The located target node is the
   first comment node child of the <doc> element.

   An example for a replacement of a processing instruction node:

   <replace sel='doc/processing-instruction("test")'><?test bar="foobar"
   ?></replace>

   This will replace the processing instruction node "test" whose parent
   is the <doc> element.

   An example for a replacement of a text node:

   <replace sel="doc/foo/text()[1]">This is the new text content</
   replace>

   This will replace the first text node child of the <foo> element.
   The positional constraint "[1]" is not usually needed as the element
   content is rarely of mixed type [6] where several text node siblings
   typically exist.

   If a text node is updated and the <replace> element is empty, the
   text node MUST thus be removed as a text node MUST always have at
   least one character of data.

4.5.  <remove> Element

   The <remove> element represents a removal operation of e.g. an
   existing element or an attribute.

   The <remove> element type has two attributes: 'sel' and 'ws'.  The



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   value of the optional 'ws' attribute is used to remove the possible
   white space text nodes that exist either as immediate following or
   preceding sibling nodes of the located target node.  The usage of
   'ws' attribute is only allowed when removing other types than text,
   attribute and namespace nodes.  If the value of 'ws' is "before", the
   purpose is to remove the immediate preceding sibling node which MUST
   be a white space text node and if the value is "after", the
   corresponding following node.  If the 'ws' value is "both", both the
   preceding and following white space text nodes MUST be removed.

   Examples for remove operations, first a removal of an element
   including all of its descendant, attribute and namespace nodes:

   <remove sel="doc/foo[@a='1']" ws="after"/>

   This will remove the <foo> element as well as the immediate following
   sibling white space text node of the <foo> element.  If the immediate
   following sibling node is not a white space text node, an error
   occurs.

   An example for a removal of an attribute node:

   <remove sel="doc/@a"/>

   This will remove the 'a' attribute node from the <doc> element.

   An example for a removal of a namespace node:

   <remove sel="doc/foo/namespace::pref"/>

   This will remove the 'pref' prefixed namespace node from the <foo>
   element.  Naturally this prefix MUST not be associated with any node
   prior to the removal of this namespace node.  Also the parent node of
   this namespace declaration MUST be the <foo> element.

   An example for a removal of a comment node:

   <remove sel="doc/comment()[1]"/>

   This will remove the first comment node child of the <doc> element.

   An example for a removal of a processing instruction node:

   <remove sel='doc/processing-instruction("test")'/>

   This will remove the "test" processing instruction node child of the
   <doc> element.




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   An example for a removal of a text node:

   <remove sel="doc/foo/text()[1]"/>

   This will remove the first text node child of the <foo> element.

   When removing an element, a comment or a processing instruction node
   which has immediate preceding and following sibling text nodes
   without the 'ws' directive, the content of these two text nodes MUST
   be combined together.  The latter text node thus disappears from the
   document.


5.  Error Handling

   It is an error condition if any of the patch operations can not be
   unambiguously fulfilled.  In other words, once a particular patch
   operation fails, it is an error condition and processing of further
   patch operations is hardly sensible.  Also it is beyond the scope of
   this document to describe a generic error response.


6.  Usage of Patch Operations

   An XML diff document SHOULD contain only the nodes which have been
   modified.  However, when there's a large collection of changes it MAY
   be desirable to exchange the full document content instead.  How this
   will be done in practice is beyond the scope of this document.


7.  Usage of Selector Values

   It is up to the application to decide the verbosity model for
   selector values.  Positional element selectors like "*/*[3]/*[2]"
   provide the shortest selectors, but care must to taken when using
   them.  When there are several removals of sibling elements, the
   positional element indexes change after each update.  Likewise these
   indexes change when new elements are inserted into the tree.  Using
   names with possible attribute predicates like "doc[@sel='foo']" is
   usually easier for an application, be it e.g. an auto diff tool but
   it leads to larger diff documents.


8.  Full Example

   An example initial XML document where namespace qualified elements
   exist:




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   <?xml version="1.0" encoding="UTF-8"?>
   <doc xmlns="urn:ietf:params:xml:ns:xxx"
        xmlns:z="urn:ietf:params:xml:ns:yyy">
     <note>This is a sample document</note>
     <elem a="foo">
       <child/>
     </elem>
     <elem a="bar">
       <z:child/>
     </elem>
   </doc>


   An imaginary XML diff document where prefix "p" corresponds the
   targetNamespace of this imaginary schema:

   <?xml version="1.0" encoding="UTF-8"?>
   <p:diff xmlns="urn:ietf:params:xml:ns:xxx"
           xmlns:y="urn:ietf:params:xml:ns:yyy"
           xmlns:p="urn:ietf:params:xml:ns:diff">

   <p:add sel="doc/elem[@a='foo']">  <!-- This is a new child -->
       <child id="ert4773">
         <y:node/>
       </child>
     </p:add>

   <p:replace sel="doc/note/text()">Patched doc</p:replace>

   <p:remove sel="*/elem[@a='bar']/y:child" ws="both"/>

   <p:add sel="*/elem[@a='bar']" type="@b">new attr</p:add>

   </p:diff>


   One possible form of the result XML document after applying the
   patches:













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   <?xml version="1.0" encoding="UTF-8"?>
   <doc xmlns="urn:ietf:params:xml:ns:xxx"
        xmlns:z="urn:ietf:params:xml:ns:yyy">
     <note>Patched doc</note>
     <elem a="foo">
       <child/>
       <!-- This is a new child -->
       <child id="ert4773">
         <z:node/>
       </child>
     </elem>
     <elem a="bar" b="new attr"/>
   </doc>


   The <node> and removed <child> element prefixes within the XML diff
   document are different than what are the "identical" namespace
   declarations in the initial XML document.  If the initial XML
   document had used a prefixed namespace declaration instead of the
   default one, the XML diff document could still have been the same.
   The added new qualified elements would just have inherited that
   prefix.


9.  XML Schema

   The schema types for the patch operation elements.

   <?xml version="1.0" encoding="UTF-8"?>
   <!DOCTYPE schema [
    <!ENTITY ncname "[^:\I][^:\C]*">
    <!ENTITY qname  "(&ncname;:)?&ncname;">
    <!ENTITY aname  "@&qname;">
    <!ENTITY pos    "\[\d+\]">
    <!ENTITY attr   "\[&aname;='(.)*'\]|\[&aname;=&quot;(.)*&quot;\]">
    <!ENTITY valueq "\[(&qname;|\.)=&quot;(.)*&quot;\]">
    <!ENTITY value  "\[(&qname;|\.)='(.)*'\]|&valueq;">
    <!ENTITY cond   "&attr;|&value;|&pos;">
    <!ENTITY step   "(&qname;|\*)(&cond;)*">
    <!ENTITY piq    "processing-instruction\((&quot;&ncname;&quot;)?\)">
    <!ENTITY pi     "processing-instruction\(('&ncname;')?\)|&piq;">
    <!ENTITY id     "id\(('&ncname;')?\)|id\((&quot;&ncname;&quot;)?\)">
    <!ENTITY com    "comment\(\)">
    <!ENTITY text   "text\(\)">
    <!ENTITY nspa   "namespace::&ncname;">
    <!ENTITY child  "&step;|&com;(&pos;)?|&text;(&pos;)?|&pi;(&pos;)?">
    <!ENTITY last   "&child;|&aname;|&nspa;">
   ]>



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   <xsd:schema
        xmlns:xsd="http://www.w3.org/2001/XMLSchema"
        elementFormDefault="qualified">

     <xsd:simpleType name="xpath">
       <xsd:restriction base="xsd:string">
         <xsd:pattern value="(/)?(&step;/)*(&last;)"/>
         <xsd:pattern value="(/)?&id;((/&step;)*(/&last;))?"/>
       </xsd:restriction>
     </xsd:simpleType>

     <xsd:simpleType name="xpath-add">
       <xsd:restriction base="xsd:string">
         <xsd:pattern value="(/)?(&step;/)*(&child;)"/>
         <xsd:pattern value="(/)?&id;((/&step;)*(/&child;))?"/>
       </xsd:restriction>
     </xsd:simpleType>

     <xsd:simpleType name="pos">
       <xsd:restriction base="xsd:string">
         <xsd:enumeration value="before"/>
         <xsd:enumeration value="after"/>
         <xsd:enumeration value="prepend"/>
       </xsd:restriction>
     </xsd:simpleType>

     <xsd:simpleType name="type">
       <xsd:restriction base="xsd:string">
         <xsd:pattern value="&aname;"/>
         <xsd:pattern value="&nspa;"/>
       </xsd:restriction>
     </xsd:simpleType>

     <xsd:complexType name="add">
       <xsd:complexContent mixed="true">
         <xsd:restriction base="xsd:anyType">
           <xsd:sequence>
             <xsd:any processContents="lax" namespace="##any"
                      minOccurs="0" maxOccurs="unbounded"/>
           </xsd:sequence>

           <xsd:attribute name="sel" type="xpath-add"
                          use="required"/>
           <xsd:attribute name="pos" type="pos"/>
           <xsd:attribute name="type" type="type"/>
         </xsd:restriction>
       </xsd:complexContent>
     </xsd:complexType>



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     <xsd:complexType name="replace">
       <xsd:complexContent mixed="true">
         <xsd:restriction base="xsd:anyType">
           <xsd:sequence>
             <xsd:any processContents="lax" namespace="##any"
                      minOccurs="0" maxOccurs="1"/>
           </xsd:sequence>

           <xsd:attribute name="sel" type="xpath" use="required"/>
         </xsd:restriction>
       </xsd:complexContent>
     </xsd:complexType>

     <xsd:simpleType name="ws">
       <xsd:restriction base="xsd:string">
         <xsd:enumeration value="before"/>
         <xsd:enumeration value="after"/>
         <xsd:enumeration value="both"/>
       </xsd:restriction>
     </xsd:simpleType>

     <xsd:complexType name="remove">
       <xsd:attribute name="sel" type="xpath" use="required"/>
       <xsd:attribute name="ws" type="ws"/>
     </xsd:complexType>

   </xsd:schema>



10.  IANA Considerations

10.1.  XML Schema Registration

   This section registers a new XML Schema.

      URI:
      urn:ietf:params:xml:schema:xml-patch-ops

      Registrant Contact:
      IETF, SIMPLE working group, <simple@ietf.org>
      Jari Urpalainen, <jari.urpalainen@nokia.com>


11.  Security Considerations

   Information exchanged within these patch operations can be highly
   sensitive.  Thus systems need to protect the integrity and



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   confidentiality of this data.  Especially, the transport protocol
   once it is used SHOULD have capabilities to protect from possible
   threats.  For example, a malicious man-in-the-middle attack could
   easily give misinformation.  However, all the security considerations
   depend very much on the application which utilizes this framework.


12.  Acknowledgments

   The author would like to thank Eva Leppanen, Mikko Lonnfors, Aki
   Niemi, Jonathan Rosenberg, Miguel A. Garcia, Anat Angel and Stephane
   Bortzmeyer for their valuable comments and Ted Hardie for his input
   and support.


13.  References

13.1.  Normative References

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [2]  "Extensible Markup Language (XML) 1.0 (Third Edition)", W3C
        Recommendation REC-xml-20040204 , February 2004.

   [3]  "XML Path Language (XPath) Version 1.0", W3C Recommendation REC-
        xpath-19991116 , November 1999.

   [4]  "Canonical XML 1.0", W3C Recommendation REC-xml-c14n-20010315 ,
        March 2001.

   [5]  "Namespaces in XML", W3C Recommendation REC-xml-names-19990114 ,
        January 1999.

   [6]  "XML Schema Part 1: Structures Second Edition", W3C
        Recommendation REC-xmlschema-1-20041028 , October 2004.

   [7]  "XML Schema Part 2: Datatypes Second Edition", W3C
        Recommendation PER-xmlschema-2-20040318 , October 2004.

   [8]  "xml:id Version 1.0 W3C Recommendation 9 September 2005", W3C
        Recommendation PR-xml-id-20050712 , September 2005.

   [9]  Yergeau, F., "UTF-8, a transformation format of ISO 10646",
        RFC 2279, January 1998.






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13.2.  Informative References

   [10]  "XML Path Language (XPath) Version 2.0", W3C Candidate
         Recommendation 3 20051103 , November 2005.

   [11]  Murata, M., "XML media types", RFC 3023, January 2001.

   [12]  Roach, A., "Session Initiation Protocol (SIP)-Specific Event
         Notification", RFC 3265, June 2002.

   [13]  Lonnfors, M., Leppanen, E., Khartabil, H., and J. Urpalainen,
         "Presence Information Data format (PIDF) Extension for Partial
         Presence",  draft-ietf-simple-partial-pidf-format-06 (work in
         progress), March 2006.

   [14]  Rosenberg, J., "An Extensible Markup Language (XML) Document
         Format For Indicating Changes in XML Configuration Access
         Protocol (XCAP) Resources",  draft-ietf-simple-xcap-diff-0x
         (work in progress), ? 2006.

   [15]  Rosenberg, J., "The Extensible Markup Language (XML)
         Configuration Access Protocol (XCAP)",
          draft-ietf-simple-xcap-08, October 2005.

   [16]  Peterson, J., "Common Profile for Presence (CPP)", RFC 3859,
         August 2004.

   [17]  Sugano, H., "CPIM presence information data format", RFC 3863,
         May 2003.

   [18]  Niemi, A., "Session Initiation Protocol (SIP) Extension for
         Event State Publication", RFC 3903, October 2004.



















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Author's Address

   Jari Urpalainen
   Nokia Research Center
   Itamerenkatu 11-13
   Helsinki  00180
   Finland

   Phone: +358 7180 37686
   Email: jari.urpalainen@nokia.com









































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