R: Look up an element via the XML catalog mechanism
catalogResolve
R Documentation
Look up an element via the XML catalog mechanism
Description
XML parsers use a catalog to map generic system and public addresses
to actual local files or potentially different remote files.
We can use a catalog to map a reference such as
http://www.omegahat.net/XSL/ to a particular
directory on our local machine and then not have to
modify any of the documents if we move the local files to another
directory, e.g. install a new version in an alternate directory.
This function provides a mechanism to query the catalog to
resolve a URI, PUBLIC or SYSTEM identifier.
This is now vectorized, so accepts a character vector of
URIs and recycles type to have the same length.
If an entry is not resolved via the catalog system,
a NA is returned for that element.
To leave the value unaltered in this case, use asIs = TRUE .
Usage
catalogResolve(id, type = "uri", asIs = FALSE, debug = FALSE)
Arguments
id
the name of the (generic) element to be resolved
type
a string, specifying whether the lookup is for a uri,
system or public element
asIs
a logical. If TRUE any element of id which
is not resolved by the catalog system will be left as given in the
call. If FALSE, such unresolved elements are identified
by NA.
debug
logical value indicating whether to turn on debugging
output written to the console (TRUE) or not (FALSE).
Value
A character vector. If the element was resolved,
the single element is the resolved value.
Otherwise, the character vector will contain no elements.
if(!exists("Sys.setenv")) Sys.setenv = Sys.putenv
Sys.setenv("XML_CATALOG_FILES" = system.file("exampleData", "catalog.xml", package = "XML"))
catalogResolve("-//OASIS//DTD DocBook XML V4.4//EN", "public")
catalogResolve("http://www.omegahat.net/XSL/foo.xsl")
catalogResolve("http://www.omegahat.net/XSL/article.xsl", "uri")
catalogResolve("http://www.omegahat.net/XSL/math.xsl", "uri")
# This one does not resolve anything, returning an empty value.
catalogResolve("http://www.oasis-open.org/docbook/xml/4.1.2/foo.xsl", "uri")
# Vectorized and returns NA for the first and /tmp/html.xsl
# for the second.
catalogAdd("http://made.up.domain", "/tmp")
catalogResolve(c("ddas", "http://made.up.domain/html.xsl"), asIs = TRUE)