SIMPLE WG                                                  J. Urpalainen
Internet-Draft                                     Nokia Research Center
Expires: May 29, 2006                                  November 25, 2005


An Extensible Markup Language (XML) Patch Operations Framework Utilizing
                  XML Path Language (XPath) Selectors
                   draft-ietf-simple-xml-patch-ops-00

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Copyright Notice

   Copyright (C) The Internet Society (2005).

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.  With the aid of these selector values and updated data
   content a set of patches can then be applied to an existing initial



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   XML document.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Basic features and requirements  . . . . . . . . . . . . . . .  4
   4.  Patch operations . . . . . . . . . . . . . . . . . . . . . . .  5
     4.1.  <add> element  . . . . . . . . . . . . . . . . . . . . . .  7
     4.2.  <replace> element  . . . . . . . . . . . . . . . . . . . .  9
     4.3.  <remove> element . . . . . . . . . . . . . . . . . . . . . 11
     4.4.  <patch> element  . . . . . . . . . . . . . . . . . . . . . 12
   5.  Error handling . . . . . . . . . . . . . . . . . . . . . . . . 13
   6.  Usage of patch operations  . . . . . . . . . . . . . . . . . . 13
   7.  Full example . . . . . . . . . . . . . . . . . . . . . . . . . 13
   8.  XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . . 14
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 17
     9.1.  XML Schema Registration  . . . . . . . . . . . . . . . . . 17
   10. Security considerations  . . . . . . . . . . . . . . . . . . . 17
   11. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 18
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
     12.1. Normative references . . . . . . . . . . . . . . . . . . . 18
     12.2. Informative references . . . . . . . . . . . . . . . . . . 18
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 20
   Intellectual Property and Copyright Statements . . . . . . . . . . 21

























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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) [14] compatible presence system, in which presence data is
   represented using the XML based Presence Information Data Format
   (PIDF) [15].  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 a document.

   This document describes an XML patch framework which utilizes XML
   Path language (XPath) [3] selectors.  With the aid of these selector
   values and updated data content a set of patches can then be applied
   to an existing initial XML document in order to transform it into a
   new patched XML document.  This document does not describe a full XML
   diff format, only basic patch operations which can be included within
   the full format.

   An XPath selector is used to locate a single unique node from the
   existing initial XML document.  Once the XML node which pinpoints the
   target for the modification has been found, modifications like
   additions, removals or substitutions of e.g. elements and attributes
   can be done.

   As an example, in the Session Initiation Protocol (SIP) [16] 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, the patch
   operations can be used in any application that exchanges XML
   documents, e.g. in the SIP Events framework [12].


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 [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 get a patched XML document
      from the initial 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 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.

   Whitespace text node: A text node which contains only whitespace.


3.  Basic features and requirements

   The changes of an XML document content, or synonymously patch
   operations as used in this document, are described by defining schema
   types for elements with the W3C Schema language [6].  The elements
   defined according to these types MUST then be embedded within an
   application specific XML diff document.  The specifications utilizing
   these element types MUST then define the full XML diff format with an
   appropriate MIME type [11].  For example the partial PIDF format [13]
   includes these schema element types.

   As the schema defined in this document does not declare any target
   namespace, elements defined according to these types inherit the
   target namespace of the including schema.  Therefore, additional
   unnecessary namespace declarations within the instance XML diff



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   documents can be avoided.

   It is anticipated that applications using these types will define
   <add>, <replace>, <remove> and <patch> elements from the
   corresponding types defined in this schema.  As this specification
   defines only types for elements, an application utilizing this
   framework can easily omit some of these type definitions which it
   doesn't need.  With these basic operations a simple patch model for
   data oriented documents [7] is produced.  On the other hand, the
   semantics described in this document can easily be extended as these
   patch operations provide only the basic required features.

   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 and
   the root node of the initial 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 of
   the document root element is not allowed as that would result in an
   invalid XML document.

   The aim of this document is to describe a deterministic framework
   where only a single possible canonical form [4] of an XML document
   exists once the patches have been applied onto it.  Especially
   whitespace text nodes MUST be processed properly in order to fulfil
   this requirement as all whitespace is not insignificant [4].


4.  Patch operations

   A full XML diff document contains a collection of patch operation
   elements: <add>, <replace>, <remove> and <patch> or a subset of these
   operations.  They will be applied sequentially to the initial XML
   document in the given document order of the XML diff document.  Other
   elements than <patch> update the structure of the initial XML
   document.  The <patch> element MAY be used with document oriented
   models [7] to update text content.

   Each of these patch operation elements 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 value of the 'sel'
   attribute is used to locate a single unique target node from the
   initial XML document.

   While the XPath recommendation specifies that prefixes can be used in



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   location steps, it does not specify how associated namespace URIs are
   to be found during the XPath evaluations.  In this 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 the prefixes are easily found from the XML diff document.
   XPath allows using "namespace-uri()" and "local-name()" node-set
   functions within XPath predicates.  For instance, these functions may
   then be utilized if there are no other means to "register" prefixes
   with associated namespace URIs.  The schema type definitions for
   these elements do not allow the usage of these node-set functions.

   It should be emphasized that prefixes within the XPath selectors MAY
   not have to be the same than that of the initial XML document because
   the equivalence of nodes is based on the same namespace URIs and
   local names.

   If a patch operation element has an in-scope default namespace
   declaration and a prefix is not used in a node test then that name is
   interpreted as if it had had a prefixed name associated with this
   default namespace URI.  That is, unlike in XPath 1.0, a namespace
   qualified element is being searched.

   When locating the target node for a patch operation from the initial
   XML document, all XPath selections start from the root node of the
   document.  Relative location paths SHOULD then be used so that the
   starting root node selection "/" can be omitted.  When locating
   elements in the document tree, the node test can be either a "*"
   character or a QName.  A "*" character selects all element children
   of the context node.  Attribute value comparisons MAY be used as
   predicates.  Also text content 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()".  Positional constraints MAY
   also be used as an additional predicate.  Ordering of these
   positional constraints and value comparisons can interchange.

   An XPath "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 the instance document.

   As all the namespace declarations relevant to the patch operations
   are included in the XML diff document, the elements within the
   changed data content are usually namespace qualified.  As with XPath
   selectors, the prefixes of these nodes are not significant only the
   namespace URIs MUST match.  For example when adding a new qualified
   element to the initial XML document, the namespace declaration which



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   has the same namespace URI is attached to this new element.  However,
   if overlapping in-scope namespaces exist within the evaluation
   context, i.e., there are several in-scope namespaces with the same
   namespace URI, then the namespace with the same prefix MUST be
   selected.  This kind of overlapping can happen when e.g. a qualified
   attribute is added while elements are attached with an equal default
   namespace declaration.

   If the intention is to add new namespace declarations to the initial
   XML document, the new namespaces MUST be declared within the added or
   changed data content embedded as local declarations within elements,
   or they MUST be explicitly added by using XPath namespace axis
   semantics shown later in this document.

4.1.  <add> element

   The <add> element represents the addition of some new content to the
   initial XML document: e.g., a new XML element or an attribute.

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

   The value of the 'sel' attribute is used to locate a single unique
   element from the initial XML document.  It is an error condition if
   multiple elements are found during the evaluation of this selector
   value.

   The value of the optional 'type' attribute is used to describe the
   type of the new data content.  The new data content, which MUST not
   be empty exists as the child node(s) of this <add> element.  The
   value of 'type' attribute is also an XPath 1.0 compatible selector
   with a very limited set of XPath features.  Once the new content
   within the <add> element contains elements, they will include all the
   attribute, namespace and descendant nodes.  As the default value of
   the 'type' attribute is "node()" the new content can be element,
   text, comment or processing instruction nodes or a mixture of them.
   The "node()" selector value is an abbreviated form of "child::
   node()".  A positional constraint MAY be used with the "node()"
   selector when only a single node needs to be added.  If the value of
   the 'type' attribute equals "@attr" the purpose is to add a new
   'attr' attribute.  The value of the 'attr' attribute is then the text
   content of the <add> element.  The less frequently used, prefixed,
   i.e. namespace 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 content of the
   <add> element is then the corresponding namespace URI.

   The value of the optional 'pos' attribute indicates the positioning
   of the new data content.  As the default value is "to", the new



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   content is then simply added onto the located target element.  For
   other node types than attribute and namespace nodes, new content is
   appended as the last child node(s).  With the value of "before" the
   new content MUST be the closest preceding sibling node(s) and with
   "after" the closest following sibling node(s).  Naturally the usage
   of 'pos' attribute is not allowed when adding attributes and
   namespaces.  It can be used e.g. when a comment node or an element is
   added just before or after an existing element.

   Appending elements with all the descendant and attribute nodes is the
   most typical operation.  Because 'type' and 'pos' attributes have
   convenient default values, the <add> element SHOULD then only contain
   the 'sel' attribute with the added content.

   Some examples without any prefixes in XPath selectors and elements
   are also not namespace qualified.  The initial XML document could be
   like the full example shown later in this document.  The full 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 of the <doc>
   element.  The located target node: the <doc> element is naturally the
   root element of the initial XML document.  The <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].

   It should be noted that as the 'sel' selector value MAY contain
   quotation marks, escaped forms: "&quot;" or "&apos;" can then 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 namespace declaration:



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   <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 the closest preceding sibling node.  This shows how a 'pos'
   attribute directive MAY be used.

   Some complexity arises when so called whitespace text nodes exist
   within the initial XML document.  The XPath 1.0 data model requires
   that a text node MUST not have another text node as a 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 in this example has then two child nodes: a
   whitespace 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 whitespace text node content MUST then be combined
   together.  Otherwise whitespace 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.

   If text nodes contain other than pre-defined entities [2] their
   declarations MUST typically be within the prolog of the XML diff
   document if the initial XML document is also referencing these
   entities.

4.2.  <replace> element

   The <replace> element represents a replacement operation: e.g. an
   existing XML element is updated with a new XML 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 an attribute: 'sel'.  The value of
   this attribute is used to select a single unique node from the
   initial XML document.  If the located target node is an element, a
   comment or a processing instruction, then the child of the <replace>



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   element MUST also be of the same type.  Otherwise the <replace>
   element MUST have text content or it MAY be empty, i.e. it does not
   have any child node.

   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", i.e. 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 content</replace>

   This will replace the attribute 'a' content of the <doc> element with
   the value "new content".  If the <replace> element has not a child
   text node, i.e. not any content, 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 the comment node.  The located target node is the
   first child comment node 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:



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

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

   If a text node is being updated and the <replace> element has not any
   child node, the text node MUST thus be removed.

4.3.  <remove> element

   The <remove> element represents a removal operation of e.g. an
   existing XML element or an attribute from the initial XML document.

   The <remove> element type has two attributes: 'sel' and 'ws'.  The
   value of the 'sel' attribute is used to select a single unique node
   from the initial XML document.  The value of the optional 'ws'
   attribute is used to remove the possible whitespace text nodes that
   exist either as the closest following or preceding sibling node(s) of
   the located target node.  The usage of 'ws' attribute is only allowed
   when removing other types than text, attribute and namespace nodes.
   As the default value of 'ws' attribute is "none", removal of
   whitespace nodes is thus not requested.  If the value of 'ws' is
   "before", the purpose is to remove the closest preceding sibling node
   which MUST be a whitespace text node and if the value is "after", the
   corresponding following node.  If the 'ws' value is "both", both the
   preceding and following whitespace text nodes MUST be removed.

   Examples for remove operations, first a removal of an element
   including all descendants, attributes and namespape nodes:

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

   This will remove the <foo> element as well as the closest following
   sibling whitespace text node of the <foo> element.  If the following
   sibling node is not a whitespace 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"/>



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   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 child comment node of the <doc> element.

   An example for a removal of a processing instruction node:

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

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

   An example for a removal of a text node:

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

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

   If an element, a comment node or a processing instruction node which
   has a whitespace text node as both the closest preceding and
   following node, is removed without a request to remove whitespace
   nodes, the content of these two nodes MUST be combined together.  The
   other whitespace text node thus disappears from the initial XML
   document.

4.4.  <patch> element

   This element type describes patching of a text node content or an
   attribute value.  There are several text patching algorithms
   available.  The <patch> element type shows how these algorithms can
   be integrated with this framework.

   The <patch> element type has two attributes: 'sel' and 'method'.  The
   value of the 'sel' attribute is used to select a single unique text
   node or an attribute from the initial XML document.  The 'method'
   value indicates the patch algorithm one of which could be e.g.
   "vcdiff" [9].  As XML is not good at embedding binary data the text
   diffing content MUST be included with BASE64 encoding [10].

   An example for a text node patch operation:

   <patch sel="doc/foo/text()"



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   >1sPEAAAAFhAAEAEAcmVsYXggbmcgaXMgY29vbBGA</patch>

   After locating the child text node of the <foo> element, BASE64 diff
   content is decoded and a relevant patch is applied to the target
   node.


5.  Error handling

   It is an error condition if any of the given operations can not be
   unambiguously fulfilled.  However, it is beyond the scope of this
   document to describe a generic error response.


6.  Usage of patch operations

   The 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 transport the full document content instead.  How
   this will be done in practice is beyond the scope of this document.


7.  Full example

   An example initial XML document where namespace qualified elements
   exist:

   <?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:









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   <?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:

   <?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> element prefix within the XML diff document is different
   than what is the same namespace declaration 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 updated qualified elements would then
   have inherited the prefixes of the initial XML document.


8.  XML Schema




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   The element schema types for the patch operations.

   <?xml version="1.0" encoding="UTF-8"?>
   <!DOCTYPE schema [
     <!ENTITY ncname  "[^:\I][^:\C]*">
     <!ENTITY qname   "(&ncname;:)?&ncname;">
     <!ENTITY aname   "@&qname;">
     <!ENTITY pos_t   "\[\d+\]">
     <!ENTITY attr_t  "\[&aname;=('|&quot;)(.)*('|&quot;)\]">
     <!ENTITY name_t  "\[(&qname;|\.)=('|&quot;)(.)*('|&quot;)\]">
     <!ENTITY cond    "(&attr_t;|&name_t;)?(&pos_t;)?|(&pos_t;)?(&attr_t;|&name_t;)?">
     <!ENTITY step    "(&qname;|\*)(&cond;)?">

     <!ENTITY pi      "processing-instruction\((('|&quot;)&qname;('|&quot;))?\)">
     <!ENTITY id      "id\((('|&quot;)&ncname;('|&quot;))?\)">
     <!ENTITY comm    "comment\(\)">
     <!ENTITY text    "text\(\)">
     <!ENTITY nspace  "namespace::&ncname;">
     <!ENTITY last    "&step;|&aname;|&nspace;|(&comm;(&pos_t;)?)|&text;(&pos_t;)?|&pi;(&pos_t;)?">
     <!ENTITY patch   "(&text;(&pos_t;)?)|&aname;">
   ]>
   <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-elem">
       <xsd:restriction base="xsd:string">
         <xsd:pattern value="(/)?(&step;/)*(&step;)"/>
         <xsd:pattern value="(/)?&id;(/&step;)*"/>
       </xsd:restriction>
     </xsd:simpleType>

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

     <xsd:simpleType name="pos">
       <xsd:restriction base="xsd:string">



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         <xsd:enumeration value="to"/>
         <xsd:enumeration value="before"/>
         <xsd:enumeration value="after"/>
       </xsd:restriction>
     </xsd:simpleType>

     <xsd:simpleType name="type">
       <xsd:restriction base="xsd:string">
         <xsd:pattern value="node\(\)(&pos_t;)?"/>
         <xsd:pattern value="&aname;"/>
         <xsd:pattern value="&nspace;"/>
       </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-elem"
                          use="required"/>
           <xsd:attribute name="pos" type="pos"
                          default="to"/>
           <xsd:attribute name="type" type="type"
                          default="node()"/>
         </xsd:restriction>
       </xsd:complexContent>
     </xsd:complexType>

     <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="none"/>



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         <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" default="none"/>
     </xsd:complexType>

     <xsd:complexType name="patch">
       <xsd:simpleContent>
         <xsd:extension base="xsd:base64Binary">
           <xsd:attribute name="sel" type="xpath-text"
                          use="required"/>
           <xsd:attribute name="method" type="xsd:string"
                          default="vcdiff"/>
         </xsd:extension>
       </xsd:simpleContent>
     </xsd:complexType>

   </xsd:schema>



9.  IANA Considerations

9.1.  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>


10.  Security considerations

   Information exchanged within these patch operations can be highly
   sensitive.  Thus systems need to protect the integrity and
   confidentiality of this data.  Especially, the transport protocol
   SHOULD have capabilities to protect from possible threats.





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11.  Acknowledgments

   The author would like to thank Eva Leppanen, Mikko Lonnfors, Aki
   Niemi, Jonathan Rosenberg and Miguel A. Garcia for their valuable
   comments.


12.  References

12.1.  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]   Korn, D., MacDonald, J., Mogul, J., and K. Vo, "The VCDIFF
         Generic Differencing and Compression Data Format", RFC 3284,
         June 2002.

   [10]  Josefsson, S., "The Base16, Base32, and Base64 Data Encodings",
         RFC 3548, July 2003.

12.2.  Informative references

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

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



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   [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-05 (work in
         progress), September 2005.

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

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

   [16]  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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