XQuery Functions and Accessors for URIs
There are a number of Accessors and Functions for manipulating and outputting URIs as described in XPath and XQuery Data Model :
fn:base-uri | The base URI of a node |
fn:document-uri | The URI of a document |
fn:encode-for-uri | Encodes reserved characters for use in the path of a URI |
fn:escape-html-uri | Escapes all characters except printable ASCII characters |
fn:iri-to-uri | Converts an IRI into a URI |
fn:resolve-uri | Resolves a relative URI to a base URI, returning an absolute URI |
fn:static-base-uri | The base URI from the static context |
Fn:base-uri
Fn:base-uri returns the base URI for a specified node. If the node is part of a document and its base-uri attribute is not explicitly set, fn:base-uri
defaults to the base URI of the document node.
Fn:base-uri – Signature-
fn:base-uri
() as
xs:anyURI?
fn:base-uri
($arg
as
node()?
) as
xs:anyURI?
The zero-argument version of the function returns the base URI of the context node and it is equivalent to calling fn:base-uri(.)
The single-argument version of the function follows the below rules:
- If
$arg
is the empty sequence, the function returns an empty sequence. - Otherwise, the function returns the value of the
dm:base-uri
accessor applied to the node$arg
.
Fn:base-uri -Examples-
Assume that $foo = ‘http://example.org/test/test.xml’
Input: base-uri($foo)
Ouput: ‘http://example.org/test/test.xml’
Fn:document-uri
Fn:document-uri takes a document node and returns the absolute URI associated with it. It is, in fact, the inverse of fn:doc, which returns a document node based on an absolute URI.
Fn:document-uri – Signature –
Fn:document-uri
($arg
as
node()?
) as
xs:anyURI?
If $arg is empty, it returns an empty sequence.
Fn:document-uri -Examples-
Assume that $foo=’doc(http://example.org/test/test.xml)’
Input: document-uri($foo)
Output: ‘http://example.org/test/test.xml’
Fn:encode-for-uri
Fn:encode-for-uri encodes reserved characters for use in the path of a URI. URIs require some characters (ASCII and non-ASCII) to be escaped with their hexadecimal Unicode code point preceded by the percentage sign (%). All characters can be escaped, exception made for the following:
- letters a through z and A through Z
- digits 0 through 9
- hyphen (-), underscore (_), period (.), tilde (~)
Fn:encode-for-uri -Signature-
fn:encode-for-uri
($uri-part
as
xs:string?
) as
xs:string
If $uri-part is an empty sequence, it returns a zero-length string.
Fn:encode-for-uri – Examples-
Input: concat("http://www.mypage.org/", encode-for-uri("~résumé")) Output: "
http://www.mypage.org/
r%E9sum%C3%A9"
Fn:encode-html-uri
Fn:escape-html-uri escapes all characters, except made for printable US-ASCII coded character set. The function enables HTML user agents to handle attribute values that expect URIs, by replacing each character with an escape sequence.
Fn:encode-html-uri -Signature-
The escape sequence takes the form of: %fn:escape-html-uri
($uri
as
xs:string?
) as
xs:string
Fn:encode-html-uri -Examples-
Input: escape-html-uri('
http://www.mypage.org/
résumé.html
'
)
Output: 'http://www.mypage.org/
r%E9sum%C3%A9.html'
Fn:iri-to-uri
Fn:iri-to-uri transforms a xs:string containing an IRI into a URI. This function replaces each special character with an escape sequence in the form %xx
, where xx
is two hexadecimal digits (in uppercase) representing the character in UTF-8.
Fn:iri-to-uri -Signature-
fn:iri-to-uri
($iri
as
xs:string?
) as
xs:string
All characters except the following are escaped:
- Letters a through z and A through Z
- Digits 0 through 9
- Hyphen (-), underscore (_), period (.), exclamation point (!), tilde (~), asterisk (*), apostrophe(‘), parentheses (‘(‘ and ‘)’) and hash mark (#)
- Semicolon (;), forward slash (/), question mark (?), colon (:), at sign (@), ampersand (&), equals sign (=), plus sign (+), dollar sign ($), comma (,), square brackets (‘[‘ and ‘]’), and percent sign (%).
If only a specific part of a UR needs to escapedI (as opposed to an entire URI), it is recommended to use the function fn:encode-for-uri .
Fn:iri-to-uri – Examples-
Input: fn:iri-to-uri ("http://www.example.com/00/Weather/CA/Los%20Angeles#ocean")
Output: “http://www.example.com/00/Weather/CA/Los%20Angeles#ocean”
Fn:resolve-uri
Fn:resolve-uri returns an absolute URI by taking a base URI ($base) and a relative($relative) URI as arguments. In case $base is not provided, then the the base URI of the static context is used. The main difference between $base and $relative is detailed here
Fn:resolve-uri -Signature-
fn:resolve-uri
($relative
as
xs:string?
) as
xs:anyURI?
fn:resolve-uri
($relative
as
xs:string?
, $base
as
xs:string
) as
xs:anyURI?
Fn:resolve-uri -Examples-
Input: fn:resolve-uri('test', 'http://www.example.org/')
Output: ‘http://www.example.org/test'
Fn:static-base-uri
Fn:static-base-uri returns the base URI of the static context. The static context of an expression is the information that is available during static analysis of the expression, prior to its evaluation. If the base URI is undefined, an empty sequence is returned.
References:
- XQuery 1.0 and XPath 2.0 Functions and Operators (Second Edition), W3C Recommendation 14 December 2010. Available at: http://www.w3.org/TR/xpath-functions/
- XQuery, Priscilla Walmsley, O’Reilly Media, 2007
- Michael Kay, XSLT 2.0 and XPath 2.0 Programmer’s Reference (Programmer to Programmer), Wrox; 4 edition, 2008IETF.
- RFC 3987: Internationalized Resource Identifiers (IRIs). Available at: http://www.ietf.org/rfc/rfc3987.txtMozilla Developer Network XPath: https://developer.mozilla.org/en-US/docs/XPath
- XQuery Library: http://www.xqueryfunctions.com/xq/
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