NAME

    RDF::NS - Just use popular RDF namespace prefixes from prefix.cc

SYNOPSIS

      use RDF::NS '20190227';              # check at compile time
      my $ns = RDF::NS->new('20190227');   # check at runtime
    
      $ns->foaf;               # http://xmlns.com/foaf/0.1/
      $ns->foaf_Person;        # http://xmlns.com/foaf/0.1/Person
      $ns->foaf('Person');     # http://xmlns.com/foaf/0.1/Person
      $ns->uri('foaf:Person'); # http://xmlns.com/foaf/0.1/Person
    
      use RDF::NS;             # get rid if typing '$' by defining a constant
      use constant NS => RDF::NS->new('20111208');
      NS->foaf_Person;         # http://xmlns.com/foaf/0.1/Person
    
      $ns->SPAQRL('foaf');     # PREFIX foaf: <http://xmlns.com/foaf/0.1/>
      $ns->TTL('foaf');        # @prefix foaf: <http://xmlns.com/foaf/0.1/> .
      $ns->XMLNS('foaf');      # xmlns:foaf="http://xmlns.com/foaf/0.1/"
    
      # load your own mapping from a file
      $ns = RDF::NS->new("mapping.txt");
    
      # select particular mappings
      %map = $ns->SELECT('rdf,dc,foaf');
      $uri = $ns->SELECT('foo|bar|doz'); # returns first existing namespace
    
      # instances of RDF::NS are just blessed hash references
      $ns->{'foaf'};           # http://xmlns.com/foaf/0.1/
      bless { foaf => 'http://xmlns.com/foaf/0.1/' }, 'RDF::NS';
      print (scalar keys %$ns) . "prefixes\n";
      $ns->COUNT;              # also returns the number of prefixes

DESCRIPTION

    Hardcoding URI namespaces and prefixes for RDF applications is neither
    fun nor maintainable. In the end we all use more or less the same
    prefix definitions, as collected at http://prefix.cc. This module
    includes all these prefixes as defined at specific snapshots in time.
    These snapshots correspond to version numbers of this module. By
    selecting particular versions, you make sure that changes at prefix.cc
    won't affect your programs.

    The command line client rdfns is installed automatically with this
    module:

      $ rdfns rdf,foaf.ttl
      @prefix foaf: <http://xmlns.com/foaf/0.1/> .
      @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .

    This module does not require RDF::Trine, which is recommended
    nevertheless. (at least version 0.140). If you prefer RDF::NS to return
    instances of RDF::Trine::Node::Resource instead of plain strings, use
    RDF::NS::Trine. RDF::NS::URIS is a similar module that returns
    instances of URI.

    The code repository of this module contains an update script
    <https://github.com/nichtich/RDF-NS/blob/master/update.pl> to download
    the current prefix-namespace mappings from http://prefix.cc.

GENERAL METHODS

    In most cases you only need the following lowercase methods.

 new ( [ $file_or_date ] [ %options ] )

    Create a new namespace mapping from a selected file, date, or hash
    reference. The special string "any" or the value 1 can be used to get
    the newest mapping, but you should better select a specific version, as
    mappings can change, violating backwards compatibility. Supported
    options include warn to enable warnings and at to specify a date.

 "prefix"

    Returns the namespace for prefix if namespace prefix is defined. For
    instance $ns->foaf returns http://xmlns.com/foaf/0.1/.

 "prefix_name"

    Returns the namespace plus local name, if namespace prefix is defined.
    For instance $ns->foaf_Person returns http://xmlns.com/foaf/0.1/Person.

 uri ( $short | "<$URI>" )

    Expand a prefixed URI, such as foaf:Person or foaf_Person.
    Alternatively you can expand prefixed URIs with method calls, such as
    $ns->foaf_Person. If you pass an URI wrapped in < and >, it will not be
    expanded but returned as given.

SERIALIZATION METHODS

 TTL ( prefix[es] )

    Returns a Turtle/Notation3 @prefix definition or a list of such
    definitions in list context. Prefixes can be passed as single arguments
    or separated by commas, vertical bars, and spaces.

 SPARQL ( prefix[es] )

    Returns a SPARQL PREFIX definition or a list of such definitions in
    list context. Prefixes can be passed as single arguments or separated
    by commas, vertical bars, and spaces.

 XMLNS ( prefix[es] )

    Returns an XML namespace declaration or a list of such declarations in
    list context. Prefixes can be passed as single arguments or separated
    by commas, vertical bars, and spaces.

 TXT ( prefix[es] )

    Returns a list of tabular-separated prefix-namespace-mappings.

 BEACON ( prefix[es] )

    Returns a list of BEACON format prefix definitions (not including
    prefixes).

LOOKUP METHODS

 PREFIX ( $uri )

    Get a prefix of a namespace URI, if it is defined. This method does a
    reverse lookup which is less performant than the other direction. If
    multiple prefixes are defined, the first in sorted order is returned.
    If you need to call this method frequently and with deterministic
    response, better create a reverse hash (method REVERSE).

 PREFIXES ( $uri )

    Get all known prefixes of a namespace URI in sorted order.

 REVERSE

    Calling $ns->REVERSE is equal to RDF::SN->new($ns). See RDF::SN for
    details.

 SELECT ( prefix[es] )

    In list context, returns a sorted list of prefix-namespace pairs, which
    can be used to assign to a hash. In scalar context, returns the
    namespace of the first prefix that was found. Prefixes can be passed as
    single arguments or separated by commas, vertical bars, and spaces.

INTERNAL METHODS

 SET ( $prefix => $namespaces [, $warn ] )

    Set or add a namespace mapping. Errors are ignored unless enabled as
    warnings with the third argument. Returns true if the mapping was
    successfully added.

 MAP ( $code [, prefix[es] ] )

    Internally used to map particular or all prefixes. Prefixes can be
    selected as single arguments or separated by commas, vertical bars, and
    spaces. In scalar context, $_ is set to the first existing prefix (if
    found) and $code is called. In list context, found prefixes are sorted
    at mapped with $code.

 GET ( $uri )

    This method is used internally to create URIs as return value of the
    URI method and all lowercase shortcut methods, such as foaf_Person. By
    default it just returns $uri unmodified.

SEE ALSO

    There are several other CPAN modules to deal with IRI namespaces, for
    instance RDF::Trine::Namespace, RDF::Trine::NamespaceMap,
    URI::NamespaceMap, RDF::Prefixes, RDF::Simple::NS,
    RDF::RDFa::Parser::Profile::PrefixCC, Class::RDF::NS, XML::Namespace,
    XML::CommonNS etc.

COPYRIGHT AND LICENSE

    This software is copyright (c) 2013- by Jakob Voß.

    This is free software; you can redistribute it and/or modify it under
    the same terms as the Perl 5 programming language system itself.

