| Rfc | 5261 |
|---|
| Title | An Extensible Markup Language (XML) Patch Operations Framework
Utilizing XML Path Language (XPath) Selectors |
|---|
| Author | J. Urpalainen |
|---|
| Date | September 2008 |
|---|
| Format: | TXT, HTML |
|---|
| Status: | PROPOSED STANDARD |
|---|
|
Network Working Group J. Urpalainen
Request for Comments: 5261 Nokia
Category: Standards Track September 2008
An Extensible Markup Language (XML) Patch Operations Framework Utilizing
XML Path Language (XPath) Selectors
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
Extensible Markup Language (XML) documents are widely used as
containers for the exchange and storage of arbitrary data in today's
systems. In order to send changes to an XML document, an entire copy
of the new version must be sent, unless there is a means of
indicating only the portions that have changed. 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.
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 ................................................5
4.1. Locating the Target of a Patch .............................6
4.2. Namespace Mangling .........................................6
4.2.1. Namespaces Used in Selectors ........................7
4.2.2. Departures from XPath Requirements ..................7
4.2.3. Namespaces and Added/Changed Content ................8
4.3. <add> Element .............................................10
4.3.1. Adding an Element ..................................11
4.3.2. Adding an Attribute ................................11
4.3.3. Adding a Prefixed Namespace Declaration ............12
4.3.4. Adding Node(s) with the 'pos' Attribute ............12
4.3.5. Adding Multiple Nodes ..............................12
4.4. <replace> Element .........................................13
1. Introduction
Extensible Markup Language (XML) [W3C.REC-xml-20060816] documents are
widely used as containers for the exchange and storage of arbitrary
data in today's systems. In order to send changes to an XML
document, an entire copy of the new version must be sent, unless
there is a means of indicating only the portions that have changed
(patches).
This document describes an XML patch framework that utilizes XML Path
language (XPath) [W3C.REC-xpath-19991116] selectors. An XPath
selector is used to pinpoint the specific portion of the XML that is
the target for the 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 target XML document. With these patch operations, a simple
semantics for data oriented XML documents
[W3C.REC-xmlschema-2-20041028] 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 that can be embedded
within a full format that typically has additional semantics.
As one concrete example, in the Session Initiation Protocol (SIP)
[RFC3903] based presence system a partial PIDF XML document format
[RFC5262] consists of the existing Presence Information Data Format
(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 [RFC3265]. Yet another example is XCAP-diff
[SIMPLE-XCAP], which uses this framework for sending partial updates
of changes to XCAP [RFC4825] resources.
2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119, BCP 14
[RFC2119] and indicate requirement levels for compliant
implementations.
The following terms are used in this document:
Target XML document: A target XML document that is going to be
updated with a set of patches.
XML diff document: An XML document that contains patch operation
elements, namespace declarations, and all the document content
changes that are needed in order to transform a target 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 target XML document.
Patch operation: A single change, i.e., a patch that is being
applied to update a target XML document.
Patch operation element: An XML element that represents a single
patch operation.
Type definition for an element: A World Wide Web Consortium (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 (qualified name)
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 that was found from the target XML
document with the aid of an XPath selector value.
White space text node: A text node that 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 specify the
modification to be performed: <add>, <replace>, or <remove>. These
elements (patch operations) are defined by schema types with the W3C
Schema language [W3C.REC-xmlschema-1-20041028]. 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.
XML documents that 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 [W3C.REC-xml-c14n-20010315] of an XML
document determines logical equivalence. For example, white space
text nodes MUST be processed properly in order to fulfill this
requirement as white space is by default significant
[W3C.REC-xml-c14n-20010315].
The specifications referencing these element schema types MUST define
the full XML diff format with an appropriate MIME type [RFC3023] and
a character set, e.g., UTF-8 [RFC3629]. For example, the partial
PIDF format [RFC5262] 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 [W3C.REC-xmlschema-2-20041028], 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 for example XML entities [W3C.REC-xml-20060816] 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.
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 a
target XML document, the patched XML document becomes a new
independent XML document against which the next patch will be
applied. This procedure repeats until all patches have successfully
been processed.
4.1. Locating the Target of 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 target XML document. This
located node pinpoints the target for a change and usually it is an
element, which is for example 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 [W3C.REC-xml-names-20060816]. 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 [W3C.REC-xmlschema-2-20041028] or with non-validating XML
parsers, an "xml:id" [W3C.WD-xml-id-20041109] attribute MUST have
been used within an instance document.
4.2. Namespace Mangling
The normal model for namespace prefixes is that they are local in
scope. Thus, an XML diff document MAY have different prefixes for
the namespaces used in the target document. The agent parsing the
diff document MUST resolve prefixes separately in both documents in
order to match the resulting QNames (qualified name) from each.
The XML diff document MUST contain declarations for all namespaces
used in the diff document. The diff document declarations are always
used to determine what namespaces apply within the diff document.
4.2.1. Namespaces Used in Selectors
A selector in a diff document may use prefixes when naming elements.
If it does use a prefix, the prefix must be looked up in the diff
document namespace declarations.
For example, the patch operation element of a diff document has an
in-scope namespace declaration "xmlns:a='foo:'" with a selector
"sel='a:bar'". The agent processing this patch MUST then look for
a 'bar' element qualified with the 'foo:' namespace regardless of
whether the 'foo:' namespace has a prefix assigned in the target
document or what that prefix is.
Default namespaces make this model a little more complicated. When
the diff document has a default namespace declaration, any element
selector without a prefix MUST be evaluated using that namespace.
For example, the patch operation element of a diff document has an
in-scope namespace declaration "xmlns='foo:'" with a selector
"sel='bar'". The agent processing this patch MUST then look for a
'bar' element qualified with the 'foo:' namespace, regardless of
whether the 'foo:' namespace has a prefix assigned in the target
document or what that prefix is.
Unqualified names are also possible. If there is no default
namespace declared, and an element name appears without a prefix,
then it is an unqualified element name. If this appears in a
selector, it MUST match an unqualified element in the target
document.
For example, the patch operation element of a diff document has
only one in-scope namespace declaration "xmlns:a='foo:'" with a
selector "sel='bar'". Since the 'bar' element has no prefix, and
there is no default namespace declaration in scope, the agent
processing this patch can only match the selector against a 'bar'
element that has no prefix and also no default namespace in scope.
4.2.2. Departures from XPath Requirements
The prefix matching rules described previously in this section are
different from those required in XPath 1.0 and 2.0
[W3C.REC-xpath20-20070123]. In XPath 1.0, a "bar" selector always
locates an unqualified <bar> element. In XPath 2.0, a "bar" selector
not only matches an unqualified <bar> element, but also matches a
qualified <bar> element that is in scope of a default namespace
declaration. In contrast, in this specification, a selector without
a prefix only matches one element, and it may match an element with
or without a prefix but only if the namespace it's qualified with (or
none) is an exact match.
The XPath 1.0 recommendation specifies "namespace-uri()" and
"local-name()" node-set functions that 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, this specification does not allow the usage of
these functions.
4.2.3. Namespaces and Added/Changed Content
Elements within the changed data content are also in scope of
namespace declarations. For example, when adding a new namespace
qualified element to the target XML document, the diff document MUST
contain a namespace declaration that applies to the element. The
agent processing the diff document MUST ensure that the target
document also contains the same namespace declaration. Similar to
XPath, the same namespace declaration in this context means that the
namespace URIs MUST be equal, but the prefixes MAY be different in
the diff and target documents.
For example, if a new added <a:bar> element has a namespace
declaration reference to "xmlns:a='foo:'" in the diff document and
the target document has only a single in-scope namespace
declaration "xmlns:b='foo:'" at the insertion point, the namespace
reference MUST be changed so that a <b:bar> element will then
exist in the patched document. The same rule applies although
default namespaces were used in either or both of the documents,
the namespace URIs determine what will be the correct references
(prefixes) in the patched document.
When the new or changed content has elements that declare new
namespaces (locally scoped), these declarations are copied unaltered
(prefix and everything) from the XML diff document to the target XML
document. Default namespace declarations can only be added in this
way, but prefixed namespace declarations MAY be added or removed with
XPath namespace axis semantics shown later in this document (look
Section 4.3.3).
A fairly difficult use case for these rules is found when the target
document has several namespace declarations in scope for the same
namespace. A target document might declare several different
prefixes for the same namespace. Normally, the agent applying the
diff document chooses *the* appropriate prefix for adding new
elements to the target document, but in this special case there's
more than one. These requirements create deterministic behavior for
this special and in practice rare case:
- If the diff document happens to use a prefix that is one of the
prefixes declared for the same namespace in the evaluation context
node of the target document, this prefix MUST be used in the
resulting patched document. An empty evaluable prefix and an
existing in-scope default namespace declaration means that the
default namespace MUST be chosen. In other words, the expanded
names are then equal within the diff and patched documents.
In an <add> operation, the evaluation context node is the
parent element of the inserted node, for example, with a
selector "sel='*/ bar'" and without a 'pos' attribute directive
(look Section 4.3), it is the <bar> element of the root
document element. With modifications of elements, the
evaluation context node is the parent element of the modified
element, and in the previous example thus the root document
element.
- Secondly, the prefix (also empty) of the evaluation context node
MUST be chosen if the namespace URIs are equal.
- Lastly, if the above two rules still don't apply, first all
in-scope namespace prefixes of the evaluation context node are
arranged alphabetically in an ascending order. If a default
namespace declaration exists, it is interpreted as the first entry
in this list. The prefix from the list is then chosen that appears
as the closest and just before the compared prefix if it were
inserted into the list. If the compared prefix were to exist
before the first prefix, the first prefix in the list MUST be
selected (i.e., there's no default namespace).
For example, if the list of in-scope prefixes in the target
document is "x", "y" and the compared prefix in the diff
document is "xx", then the "x" prefix MUST be chosen. If an
"a" prefix were evaluated, the "x" prefix, the first entry MUST
be chosen. If there were also an in-scope default namespace
declaration, an evaluable "a" prefix would then select the
default declaration. Note that unprefixed attributes don't
inherit the default namespace declaration. When adding
qualified attributes, the default namespace declaration is then
not on this matching list of prefixes (see Section 4.3.2).
Note that these requirements might mean that a resulting patched
document could contain unused and/or superfluous namespace
declarations. The resulting patched document MUST NOT be "cleaned
up" such that these namespace declarations are removed.
Note: In practice, the agent constructing a diff document can
usually freely select the appropriate prefixes for the namespace
declarations and it doesn't need to know or care about the actual
prefixes in the target document unless there are overlapping
declarations. In other words, the diff format content is
typically independent of the target documents usage of namespace
prefixes. However, it may be very useful to know where namespaces
are declared in the target document. The most typical use case is
such though, that the agent generating a diff has both the
previous (target) and new (patched) documents available, and
namespace declarations are thus exactly known. Note also, that in
a case where the target document is not exactly known, it is
allowed to use locally scoped namespace declarations, the
consequences of which are larger and less human-readable patched
documents.
4.3. <add> Element
The <add> element represents the addition of some new content to the
target XML document: for example, 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 MAY contain any mixture of element, text, comment or
processing instruction nodes in any order. All children of the <add>
element are then copied into a target 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 string "attr" is the name of the actual attribute being added.
The value of this new 'attr' attribute is the text node 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", "pref" is the actual
prefix string to be used for the namespace declaration in the patched
document 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 that describe the use cases of these <add>
element attributes. The nodes are not namespace qualified and
prefixes are therefore not used, and the whole XML diff content is
not shown in these examples, only patch operation elements. Full
examples are given in an Appendix A.
4.3.1. Adding an Element
An example for an addition of an element:
<add sel="doc"><foo id="ert4773">This is a new child</foo></add>
Once the <doc> element has been found from the target 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 target XML document. The new <foo> element
contains an 'id' attribute and a child text node.
4.3.2. Adding an Attribute
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 that
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"
[W3C.REC-xmlschema-2-20041028].
Note that with namespace qualified attributes, the prefix matching
rules within the 'type' attribute are evaluated with similar rules
described in Section 4.2.3. Also, note that then the possible
default namespace declaration of the context element isn't
applicable.
Note: As the 'sel' selector value MAY contain quotation marks,
escaped forms: """ or "'" 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.
4.3.3. Adding a Prefixed Namespace Declaration
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".
4.3.4. Adding Node(s) with the 'pos' Attribute
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.
4.3.5. Adding Multiple Nodes
Some complexity arises when so-called white space text nodes exist
within a target 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 then has 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
there cannot 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 [W3C.REC-xml-20060816] 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 target 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: for
example, 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 only has 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.
4.4.1. Replacing an Element
An example for a replacement of an element:
<replace sel="doc/foo[@a='1']"><bar a="2"/></replace>
This will update the <foo> element that 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.
4.4.2. Replacing an Attribute Value
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
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=""/>.
4.4.3. Replacing a Namespace Declaration URI
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.
4.4.4. Replacing a Comment Node
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.
4.4.5. Replacing a Processing Instruction Node
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.
4.4.6. Replacing a Text Node
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 [W3C.REC-xmlschema-1-20041028] 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, for example,
an existing element or an attribute.
The <remove> element type has two attributes: 'sel' and 'ws'. The
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 that 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.
4.5.1. Removing an Element
An example of 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.
4.5.2. Removing an Attribute
An example for a removal of an attribute node:
<remove sel="doc/@a"/>
This will remove the 'a' attribute node from the <doc> element.
4.5.3. Removing a Prefixed Namespace Declaration
An example for a removal of a prefixed 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.
4.5.4. Removing a Comment Node
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.
4.5.5. Removing a Processing Instruction Node
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.
4.5.6. Removing a Text Node
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
that 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 cannot 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.
A new MIME error format is defined for applications that require
deterministic error handling when patching cannot be applied. It is
anticipated that these error elements can be used within other MIME
types that allow extension elements.
5.1. Error Elements
The root element of the error document is <patch-ops-error>. The
content of this element is a specific error condition. Each error
condition is represented by a different element. This allows for
different error conditions to provide different data about the nature
of the error. All error elements support a "phrase" attribute, which
can contain text meant for rendering to a human user. The optional
"xml:lang" MAY be used to describe the language of the "phrase"
attribute. Most of the error condition elements are supposed to
contain the patch operation element that caused the patch to fail.
The following error elements are defined by this specification:
<invalid-attribute-value>: The validity constraints of 'sel',
'type', 'ws', or 'pos' attribute values MAY be indicated with this
error, i.e., non-allowable content has been used. Also, this
error can be used to indicate if an added or a modified attribute
content is not valid, for example, CDATA sections were used when a
new attribute was intended to be added.
<invalid-character-set>: The patch could not be applied because the
diff and the patched document use different character sets.
<invalid-diff-format>: This indicates that the diff body of the
request was not a well-formed XML document or a valid XML document
according to its schema.
<invalid-entity-declaration>: An entity reference was found but
corresponding declaration could not be located or resolved.
<invalid-namespace-prefix>: The namespace URI for the given prefix
could not be located or resolved, e.g., within the 'sel' attribute
a prefix was used but its declaration is missing from the target
document.
<invalid-namespace-uri>: The namespace URI value is not valid or the
target document did not have this declaration.
<invalid-node-types>: The node types of a <replace> operation did
not match, i.e., for example, the 'sel' selector locates an
element but the replaceable content is of text type. Also, a
<replace> operation may locate a unique element, but replaceable
content had multiple nodes.
<invalid-patch-directive>: A patch directive could not be fulfilled
because the given directives were not understood.
<invalid-root-element-operation>: The root element of the document
cannot be removed or another sibling element for the document root
element cannot be added.
<invalid-xml-prolog-operation>: Patch failure related to XML prolog
nodes.
<invalid-whitespace-directive>: A <remove> operation requires a
removal of a white space node that doesn't exist in the target
document.
<unlocated-node>: A single unique node (typically an element) could
not be located with the 'sel' attribute value. Also, the location
of multiple nodes can lead to this error.
<unsupported-id-function>: The nodeset function id() is not
supported, and thus attributes with the ID type are not known.
<unsupported-xml-id>: The attribute xml:id as an ID attribute in XML
documents is not supported.
Additional error elements can be indicated within the root
<patch-ops-error> element from any namespace. However, the IETF MAY
specify additional error elements in the
"urn:ietf:params:xml:ns:patch-ops-error" namespace.
As an example, the following document indicates that it was attempted
to add a new <note> element with white space into a document, but the
parent element could not be located:
<?xml version="1.0" encoding="UTF-8"?>
<patch-ops-error
xmlns:p="urn:ietf:params:xml:ns:pidf-diff"
xmlns="urn:ietf:params:xml:ns:patch-ops-error">
<unlocated-node
phrase="a unique node could not be located with the id() function."
><p:add sel='id("ert4773")'>
<p:note>some text added</p:note>
</p:add></unlocated-node>
</patch-ops-error>
6. Usage of Patch Operations
An XML diff document SHOULD contain only the nodes that have been
modified as the intention is to try to reduce bandwidth/storage
requirements. However, when there's a large collection of changes it
can be desirable to exchange the full document content instead. How
this will be done in practice is beyond the scope of this document.
Some applications MAY require that the full versioning history MUST
be indicated although the history had superfluous changes. This
framework doesn't mandate any specific behavior, applications MAY
decide the appropriate semantics themselves. Also, in practice,
applications are free to select the proper algorithms when generating
diff document content.
7. Usage of Selector Values
It is up to the application to decide what kind of selector values to
use. 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 for example an auto diff tool, but
it leads to larger diff documents.
8. XML Schema Types of Patch Operation Elements
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 "\[&aname;='(.)*'\]|\[&aname;="(.)*"\]">
<!ENTITY valueq "\[(&qname;|\.)="(.)*"\]">
<!ENTITY value "\[(&qname;|\.)='(.)*'\]|&valueq;">
<!ENTITY cond "&attr;|&value;|&pos;">
<!ENTITY step "(&qname;|\*)(&cond;)*">
<!ENTITY piq "processing-instruction\(("&ncname;")\)">
<!ENTITY pi "processing-instruction\(('&ncname;')?\)|&piq;">
<!ENTITY id "id\(('&ncname;')?\)|id\(("&ncname;")?\)">
<!ENTITY com "comment\(\)">
<!ENTITY text "text\(\)">
<!ENTITY nspa "namespace::&ncname;">
<!ENTITY cnodes "(&text;(&pos;)?)|(&com;(&pos;)?)|((π)(&pos;)?)">
<!ENTITY child "&cnodes;|&step;">
<!ENTITY last "(&child;|&aname;|&nspa;)">
]>
<xsd:schema
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified">
<xsd:simpleType name="xpath">
<xsd:restriction base="xsd:string">
<xsd:pattern
value="(/)?((&id;)((/&step;)*(/&last;))?|(&step;/)*(&last;))"/>
</xsd:restriction>
</xsd:simpleType>
<xsd:simpleType name="xpath-add">
<xsd:restriction base="xsd:string">
<xsd:pattern
value="(/)?((&id;)((/&step;)*(/&child;))?|(&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;|&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>
<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>
9. XML Schema of Patch Operation Errors
The patch operation errors definitions.
<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema
targetNamespace="urn:ietf:params:xml:ns:patch-ops-error"
xmlns:tns="urn:ietf:params:xml:ns:patch-ops-error"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified"
attributeFormDefault="unqualified">
<!-- This import brings in the XML language attribute xml:lang-->
<xsd:import namespace="http://www.w3.org/XML/1998/namespace"
schemaLocation="http://www.w3.org/2001/xml.xsd"/>
<!-- ROOT document element for signaling patch-ops errors -->
<xsd:element name="patch-ops-error">
<xsd:complexType>
<xsd:sequence>
<xsd:any namespace="##any" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>
</xsd:sequence>
<xsd:anyAttribute processContents="lax"/>
</xsd:complexType>
</xsd:element>
<!-- patch-ops error elements:
not intended to be used as root documnet elements -->
<xsd:element name="invalid-attribute-value"
type="tns:patch-error"/>
<xsd:element name="invalid-character-set"
type="tns:patch-error-simple"/>
<xsd:element name="invalid-diff-format"
type="tns:patch-error-simple"/>
<xsd:element name="invalid-entity-declaration"
type="tns:patch-error"/>
<xsd:element name="invalid-namespace-prefix"
type="tns:patch-error"/>
<xsd:element name="invalid-namespace-uri"
type="tns:patch-error"/>
<xsd:element name="invalid-node-types"
type="tns:patch-error"/>
<xsd:element name="invalid-patch-directive"
type="tns:patch-error"/>
<xsd:element name="invalid-root-element-operation"
type="tns:patch-error"/>
<xsd:element name="invalid-xml-prolog-operation"
type="tns:patch-error"/>
<xsd:element name="invalid-whitespace-directive"
type="tns:patch-error"/>
<xsd:element name="unlocated-node"
type="tns:patch-error"/>
<xsd:element name="unsupported-id-function"
type="tns:patch-error"/>
<xsd:element name="unsupported-xml-id"
type="tns:patch-error"/>
<!-- simple patch-ops error type -->
<xsd:complexType name="patch-error-simple">
<xsd:attribute name="phrase" type="xsd:string"/>
<xsd:attribute ref="xml:lang"/>
<xsd:anyAttribute processContents="lax"/>
</xsd:complexType>
<!-- error type which includes patch operation -->
<xsd:complexType name="patch-error">
<xsd:sequence>
<xsd:any namespace="##any" processContents="lax"/>
</xsd:sequence>
<xsd:attribute name="phrase" type="xsd:string"/>
<xsd:attribute ref="xml:lang"/>
<xsd:anyAttribute processContents="lax"/>
</xsd:complexType>
</xsd:schema>
10. IANA Considerations
IANA has completed the following actions:
o registered a new XML namespace URN according to the procedures of
RFC 3688 [RFC3688].
o registered a new MIME type 'application/patch-ops-error+xml'
according to the procedures of RFC 4288 [RFC4288] and guidelines
in RFC 3023 [RFC3023].
o registered two XML Schemas according to the procedures of RFC 3688
[RFC3688].
10.1. URN Sub-Namespace Registration
This specification registers a new XML namespace, as per the
guidelines in RFC 3688 [RFC3688].
URI: The URI for this namespace is
urn:ietf:params:xml:ns:patch-ops-error
Registrant Contact: IETF, SIMPLE working group, (simple@ietf.org),
Jari Urpalainen (jari.urpalainen@nokia.com).
XML:
BEGIN
<?xml version="1.0"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
"http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="content-type"
content="text/html;charset=iso-8859-1"/>
<title>Patch-Ops Error Namespace</title>
</head>
<body>
<h1>Namespace for Patch-Ops Error Documents</h1>
<h2>urn:ietf:params:xml:ns:patch-ops-error</h2>
<p>See <a
href="http://www.rfc-editor.org/rfc/rfc5261.txt">RFC5261</a>.</p>
</body>
</html>
END
10.2. application/patch-ops-error+xml MIME Type
MIME media type name: application
MIME subtype name: patch-ops-error+xml
Mandatory parameters: none
Optional parameters: Same as charset parameter application/xml as
specified in RFC 3023 [RFC3023].
Encoding considerations: Same as encoding considerations of
application/xml as specified in RFC 3023 [RFC3023].
Security considerations: See Section 10 of RFC 3023 [RFC3023].
Interoperability considerations: none.
Published specification: RFC 5261
Applications which use this media type: This document type has been
used to support transport of Patch-Ops errors in RFC 5261.
Additional Information:
Magic Number: None
File Extension: .xer
Macintosh file type code: "TEXT"
Personal and email address for further information: Jari
Urpalainen, jari.urpalainen@nokia.com
Intended usage: COMMON
Author/Change controller: The IETF
10.3. Patch-Ops-Types XML Schema Registration
This section registers a new XML Schema, the sole content of which is
shown in Section 8.
URI:
urn:ietf:params:xml:schema:patch-ops
Registrant Contact:
IETF, SIMPLE working group, <simple@ietf.org>
Jari Urpalainen, <jari.urpalainen@nokia.com>
10.4. Patch-Ops-Error XML Schema Registration
This section registers a new XML Schema, the sole content of which is
shown in Section 9.
URI:
urn:ietf:params:xml:schema:patch-ops-error
Registrant Contact:
IETF, SIMPLE working group, <simple@ietf.org>
Jari Urpalainen, <jari.urpalainen@nokia.com>
11. Security Considerations
Security considerations depend very much on the application that
utilizes this framework. Since each application will have different
needs, threat models, and security features, it will be necessary to
consider these on an application-by-application basis.
However, this framework utilizes a limited subset of XPath 1.0.
Applications may thus be vulnerable to XPath injection attacks that
can reveal some non-allowable content of an XML document. Injection
attacks are most likely with shareable resources where access to a
resource is limited to only some specific parts for a user, contrary
to a typical use case of this framework. To defend against those
attacks the input MUST be sanitized which can be done, for example,
by validating the diff formats with these restrictive schemas.
12. Acknowledgments
The author would like to thank Lisa Dusseault for her efforts
including BoF arrangements, comments and editing assistance. The
author would also like to thank Eva Leppanen, Mikko Lonnfors, Aki
Niemi, Jonathan Rosenberg, Miguel A. Garcia, Anat Angel, Stephane
Bortzmeyer, Dave Crocker, Joel Halpern, Jeffrey Hutzelman, David
Ward, and Chris Newman for their valuable comments and Ted Hardie for
his input and support.
13. References
13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[W3C.REC-xml-20060816]
Maler, E., Paoli, J., Bray, T., Yergeau, F., and C.
Sperberg-McQueen, "Extensible Markup Language (XML) 1.0
(Fourth Edition)", World Wide Web Consortium
Recommendation REC-xml-20060816, August 2006,
<http://www.w3.org/TR/2006/REC-xml-20060816>.
[W3C.REC-xpath-19991116]
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>.
[W3C.REC-xml-names-20060816]
Hollander, D., Bray, T., Layman, A., and R. Tobin,
"Namespaces in XML 1.0 (Second Edition)", World Wide Web
Consortium Recommendation REC-xml-names-20060816, August
2006,
<http://www.w3.org/TR/2006/REC-xml-names-20060816>.
[W3C.REC-xmlschema-1-20041028]
Beech, D., Thompson, H., 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>.
[W3C.REC-xml-c14n-20010315]
Boyer, J., "Canonical XML Version 1.0", World Wide Web
Consortium Recommendation REC-xml-c14n-20010315, March
2001,
<http://www.w3.org/TR/2001/REC-xml-c14n-20010315>.
[W3C.REC-xmlschema-2-20041028]
Malhotra, A. and P. Biron, "XML Schema Part 2: Datatypes
Second Edition", World Wide Web Consortium Recommendation
REC-xmlschema-2-20041028, October 2004,
<http://www.w3.org/TR/2004/REC-xmlschema-2-20041028>.
[W3C.WD-xml-id-20041109]
Veillard, D., Walsh, N., and J. Marsh, "xml:id Version
1.0", W3C LastCall WD-xml-id-20041109, November 2004.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media
Types", RFC 3023, January 2001.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
January 2004.
[RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and
Registration Procedures", BCP 13, RFC 4288, December 2005.
13.2. Informative References
[W3C.REC-xpath20-20070123]
Berglund, A., Fernandez, M., Chamberlin, D., Boag, S.,
Robie, J., Kay, M., and J. Simeon, "XML Path Language
(XPath) 2.0", World Wide Web Consortium Recommendation
REC-xpath20-20070123, January 2007,
<http://www.w3.org/TR/2007/REC-xpath20-20070123>.
[RFC4825] Rosenberg, J., "The Extensible Markup Language (XML)
Configuration Access Protocol (XCAP)", RFC 4825, May 2007.
[RFC3265] Roach, A., "Session Initiation Protocol (SIP)-Specific
Event Notification", RFC 3265, June 2002.
[RFC5262] Lonnfors, M., Leppanen, E., Khartabil, H., and J.
Urpalainen, "Presence Information Data format (PIDF)
Extension for Partial Presence", RFC 5262, September 2008.
[SIMPLE-XCAP]
Urpalainen, J. and J. Rosenberg, "An Extensible Markup
Language (XML) Document Format for Indicating A Change in
XML Configuration Access Protocol (XCAP) Resources", Work
in Progress, May 2008.
[RFC3903] Niemi, A., Ed., "Session Initiation Protocol (SIP)
Extension for Event State Publication", RFC 3903, October
2004.
Appendix A. Informative Examples
All following examples assume an imaginary XML diff document
including these patch operation elements.
A.1. Adding an Element
An example target XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<note>This is a sample document</note>
</doc>
An XML diff document:
<?xml version="1.0" encoding="UTF-8"?>
<diff>
<add sel="doc"><foo id="ert4773">This is a new child</foo></add>
</diff>
A result XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<note>This is a sample document</note>
<foo id="ert4773">This is a new child</foo></doc>
A.2. Adding an Attribute
An example target XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<note>This is a sample document</note>
<foo id="ert4773">This is a new child</foo></doc>
An XML diff document:
<?xml version="1.0" encoding="UTF-8"?>
<diff>
<add sel="doc/foo[@id='ert4773']" type="@user">Bob</add>
</diff>
A result XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<note>This is a sample document</note>
<foo id="ert4773" user="Bob">This is a new child</foo></doc>
A.3. Adding a Prefixed Namespace Declaration
An example target XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<note>This is a sample document</note>
<foo id="ert4773">This is a new child</foo></doc>
An XML diff document:
<?xml version="1.0" encoding="UTF-8"?>
<diff>
<add sel="doc" type="namespace::pref">urn:ns:xxx</add>
</diff>
A result XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc xmlns:pref="urn:ns:xxx">
<note>This is a sample document</note>
<foo id="ert4773">This is a new child</foo></doc>
A.4. Adding a Comment Node with the 'pos' Attribute
An example target XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<note>This is a sample document</note>
<foo id="ert4773">This is a new child</foo></doc>
An XML diff document:
<?xml version="1.0" encoding="UTF-8"?>
<diff>
<add sel="doc/foo[@id='ert4773']" pos="before"><!-- comment --></add>
</diff>
A result XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<note>This is a sample document</note>
<!-- comment --><foo id="ert4773">This is a new child</foo></doc>
A.5. Adding Multiple Nodes
An example target XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<note>This is a sample document</note>
</doc>
An XML diff document:
<?xml version="1.0" encoding="UTF-8"?>
<diff>
<add sel="doc">
<foo id="ert4773">This is a new child</foo></add>
</diff>
A result XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<note>This is a sample document</note>
<foo id="ert4773">This is a new child</foo></doc>
A.6. Replacing an Element
An example target XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<foo a="1">This is a sample document</foo>
</doc>
An XML diff document:
<?xml version="1.0" encoding="UTF-8"?>
<diff>
<replace sel="doc/foo[@a='1']"><bar a="2"/></replace>
</diff>
A result XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<bar a="2"/>
</doc>
A.7. Replacing an Attribute Value
An example target XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc a="test">
<foo a="1">This is a sample document</foo>
</doc>
An XML diff document:
<?xml version="1.0" encoding="UTF-8"?>
<diff>
<replace sel="doc/@a">new value</replace>
</diff>
A result XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc a="new value">
<foo a="1">This is a sample document</foo>
</doc>
A.8. Replacing a Namespace Declaration URI
An example target XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc xmlns:pref="urn:test">
<foo a="1">This is a sample document</foo>
</doc>
An XML diff document:
<?xml version="1.0" encoding="UTF-8"?>
<diff>
<replace sel="doc/namespace::pref">urn:new:xxx</replace>
</diff>
A result XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc xmlns:pref="urn:new:xxx">
<foo a="1">This is a sample document</foo>
</doc>
A.9. Replacing a Comment Node
An example target XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc xmlns:pref="urn:test">
<foo a="1">This is a sample document</foo>
<!-- comment -->
</doc>
An XML diff document:
<?xml version="1.0" encoding="UTF-8"?>
<diff>
<replace sel="doc/comment()[1]"><!-- This is the new content
--></replace>
</diff>
A result XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc xmlns:pref="urn:test">
<foo a="1">This is a sample document</foo>
<!-- This is the new content
-->
</doc>
A.10. Replacing a Processing Instruction Node
An example target XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<foo a="1">This is a sample document</foo>
<?test foo="bar"?>
</doc>
An XML diff document:
<?xml version="1.0" encoding="UTF-8"?>
<diff>
<replace sel='doc/processing-instruction("test")'
><?test bar="foobar"?></replace>
</diff>
A result XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<foo a="1">This is a sample document</foo>
<?test bar="foobar"?>
</doc>
A.11. Replacing a Text Node
An example target XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<foo a="1">This is a sample document</foo>
</doc>
An XML diff document:
<?xml version="1.0" encoding="UTF-8"?>
<diff>
<replace sel="doc/foo/text()[1]"
>This is the new text content</replace></diff>
A result XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<foo a="1">This is the new text content</foo>
</doc>
A.12. Removing an Element
An example target XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<foo a="1">This is a sample document</foo>
</doc>
An XML diff document:
<?xml version="1.0" encoding="UTF-8"?>
<diff>
<remove sel="doc/foo[@a='1']" ws="after"/>
</diff>
A result XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc>
</doc>
A.13. Removing an Attribute
An example target XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc a="foo">
<foo a="1">This is a sample document</foo>
</doc>
An XML diff document:
<?xml version="1.0" encoding="UTF-8"?>
<diff>
<remove sel="doc/@a"/>
</diff>
A result XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<foo a="1">This is a sample document</foo>
</doc>
A.14. Removing a Prefixed Namespace Declaration
An example target XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<foo a="1" xmlns:pref="urn:test"
>This is a sample document</foo>
<!-- comment -->
</doc>
An XML diff document:
<?xml version="1.0" encoding="UTF-8"?>
<diff>
<remove sel="doc/foo/namespace::pref"/>
</diff>
A result XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<foo a="1">This is a sample document</foo>
<!-- comment -->
</doc>
A.15. Removing a Comment Node
An example target XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<foo a="1">This is a sample document</foo>
<!-- comment -->
</doc>
An XML diff document:
<?xml version="1.0" encoding="UTF-8"?>
<diff>
<remove sel="doc/comment()[1]" ws="after"/>
</diff>
A result XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<foo a="1">This is a sample document</foo>
</doc>
A.16. Removing a Processing Instruction Node
An example target XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<foo a="1">This is a sample document</foo>
<?test?>
</doc>
An XML diff document:
<?xml version="1.0" encoding="UTF-8"?>
<diff>
<remove sel='doc/processing-instruction("test")'/>
</diff>
A result XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<foo a="1">This is a sample document</foo>
</doc>
A.17. Removing a Text Node
An example target XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<foo a="1">This is a sample document</foo>
</doc>
An XML diff document:
<?xml version="1.0" encoding="UTF-8"?>
<diff>
<remove sel="doc/foo/text()[1]"/>
</diff>
A result XML document:
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<foo a="1"/>
</doc>
A.18. Several Patches With Namespace Mangling
An example target 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:
<?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> and removed <child> element prefixes within the XML diff
document are different than what are the "identical" namespace
declarations in the target XML document. If the target 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.
Author's Address
Jari Urpalainen
Nokia
Itamerenkatu 11-13
Helsinki 00180
Finland
Phone: +358 7180 37686
EMail: jari.urpalainen@nokia.com
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