RE: What is XPath? Is this a W3C standard or product name?

Subject: RE: What is XPath? Is this a W3C standard or product name?
From: "Fenton, Brigitte (ThomasTech)" <BFenton@xxxxxxxxxxxxxxxxxxxxxxx>
Date: Mon, 13 Nov 2000 11:59:18 -0500

I just went through a similar ordeal of looking at anything with an X-prefix
and finding out all about it (i.e. its definition, whether it is a
specification, etc.)

So, the answer is that XPath is a W3C Recommendation and you can read all
about it at:

Here is a definition right from the above-listed document:

XPath is the result of an effort to provide a common syntax and semantics
for functionality shared between XSL Transformations [XSLT] and XPointer
[XPointer]. The primary purpose of XPath is to address parts of an XML [XML]
document. In support of this primary purpose, it also provides basic
facilities for manipulation of strings, numbers and booleans. XPath uses a
compact, non-XML syntax to facilitate use of XPath within URIs and XML
attribute values. XPath operates on the abstract, logical structure of an
XML document, rather than its surface syntax. XPath gets its name from its
use of a path notation as in URLs for navigating through the hierarchical
structure of an XML document.

In addition to its use for addressing, XPath is also designed so that it has
a natural subset that can be used for matching (testing whether or not a
node matches a pattern); this use of XPath is described in XSLT.

XPath models an XML document as a tree of nodes. There are different types
of nodes, including element nodes, attribute nodes and text nodes. XPath
defines a way to compute a string-value for each type of node. Some types of
nodes also have names. XPath fully supports XML Namespaces [XML Names].
Thus, the name of a node is modeled as a pair consisting of a local part and
a possibly null namespace URI; this is called an expanded-name. The data
model is described in detail in [5 Data Model].

The primary syntactic construct in XPath is the expression. An expression
matches the production Expr. An expression is evaluated to yield an object,
which has one of the following four basic types:

node-set (an unordered collection of nodes without duplicates) 
boolean (true or false) 
number (a floating-point number) 
string (a sequence of UCS characters) 
Expression evaluation occurs with respect to a context. XSLT and XPointer
specify how the context is determined for XPath expressions used in XSLT and
XPointer respectively. The context consists of:

a node (the context node) 
a pair of non-zero positive integers (the context position and the context
a set of variable bindings 
a function library 
the set of namespace declarations in scope for the expression 
The context position is always less than or equal to the context size.

The variable bindings consist of a mapping from variable names to variable
values. The value of a variable is an object, which can be of any of the
types that are possible for the value of an expression, and may also be of
additional types not specified here.

The function library consists of a mapping from function names to functions.
Each function takes zero or more arguments and returns a single result. This
document defines a core function library that all XPath implementations must
support (see [4 Core Function Library]). For a function in the core function
library, arguments and result are of the four basic types. Both XSLT and
XPointer extend XPath by defining additional functions; some of these
functions operate on the four basic types; others operate on additional data
types defined by XSLT and XPointer.

The namespace declarations consist of a mapping from prefixes to namespace

The variable bindings, function library and namespace declarations used to
evaluate a subexpression are always the same as those used to evaluate the
containing expression. The context node, context position, and context size
used to evaluate a subexpression are sometimes different from those used to
evaluate the containing expression. Several kinds of expressions change the
context node; only predicates change the context position and context size
(see [2.4 Predicates]). When the evaluation of a kind of expression is
described, it will always be explicitly stated if the context node, context
position, and context size change for the evaluation of subexpressions; if
nothing is said about the context node, context position, and context size,
they remain unchanged for the evaluation of subexpressions of that kind of

XPath expressions often occur in XML attributes. The grammar specified in
this section applies to the attribute value after XML 1.0 normalization. So,
for example, if the grammar uses the character <, this must not appear in
the XML source as < but must be quoted according to XML 1.0 rules by, for
example, entering it as &lt;. Within expressions, literal strings are
delimited by single or double quotation marks, which are also used to
delimit XML attributes. To avoid a quotation mark in an expression being
interpreted by the XML processor as terminating the attribute value the
quotation mark can be entered as a character reference (&quot; or &apos;).
Alternatively, the expression can use single quotation marks if the XML
attribute is delimited with double quotation marks or vice-versa.

One important kind of expression is a location path. A location path selects
a set of nodes relative to the context node. The result of evaluating an
expression that is a location path is the node-set containing the nodes
selected by the location path. Location paths can recursively contain
expressions that are used to filter sets of nodes. A location path matches
the production LocationPath.

In the following grammar, the non-terminals QName and NCName are defined in
[XML Names], and S is defined in [XML]. The grammar uses the same EBNF
notation as [XML] (except that grammar symbols always have initial capital

Expressions are parsed by first dividing the character string to be parsed
into tokens and then parsing the resulting sequence of tokens. Whitespace
can be freely used between tokens. The tokenization process is described in
[3.7 Lexical Structure].

> -----Original Message-----
> From: Reich, Eric [mailto:ereich@xxxxxxxxxxxxxx]
> Sent: Monday, November 13, 2000 10:39 AM
> To: 'xsl-list@xxxxxxxxxxxxxxxx'
> Subject: What is XPath? Is this a W3C standard or product name?
> Hi, All...
> I have been asked, "What is XPath? Is this a W3C standard or  product
> name?". I did not
> have a concrete reply on the tip of my tongue. Can anyone, 
> here, help me out
> with 
> this?
> Thank you,
> Eric
>  XSL-List info and archive:

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