NAME
      Data::Stag - Structured Tags datastructures

SYNOPSIS
      # PROCEDURAL USAGE
      use Data::Stag qw(:all);
      $doc = stag_parse($file);
      @persons = stag_find($doc, "person");
      foreach $p (@persons) {
        printf "%s, %s phone: %s\n",
          stag_sget($p, "family_name"),
          stag_sget($p, "given_name"),
          stag_sget($p, "phone_no"),
        ;
      } 

      # OBJECT-ORIENTED USAGE
      use Data::Stag;
      $doc = Data::Stag->parse($file);
      @persons = $doc->find("person");
      foreach $p (@person) {
        printf "%s, %s phone:%s\n",
          $p->sget("family_name"),
          $p->sget("given_name"),
          $p->sget("phone_no"),
        ;
      }

DESCRIPTION
    This module is for manipulating data as hierarchical tag/value pairs
    (Structured TAGs or Simple Tree AGgreggates). These datastructures can
    be represented as nested arrays, which have the advantage of being
    native to perl. A simple example is shown below:

      [ person=> [  [ family_name => $family_name ],
                    [ given_name  => $given_name  ],
                    [ phone_no    => $phone_no    ] ] ],

    the Data::Stag manpage uses a subset of XML for import and export. This
    means the module can also be used as a general XML parser/writer (with
    certain caveats).

    The above set of structured tags can be represented in XML as

      <person>
        <family_name>...</family_name>
        <given_name>...</given_name>
        <phone_no>...</phone_no>
      </person>

    This datastructure can be examined, manipulated and exported using Stag
    functions or methods:

      $document = Data::Stag->parse($file);
      @persons = $document->find('person');
      foreach my $person (@person) {
        $person->set('full_name',
                     $person->sget('given_name') . ' ' .
                     $person->sget('family_name'));
      }

    Advanced querying is performed by passing functions, for example:

      # get all people in dataset with name starting 'A'
      @persons = 
        $document->where('person',
                         sub {shift->sget('family_name') =~ /^A/});

    One of the things that marks this module out against other XML modules
    is this emphasis on a functional approach as an obect-oriented or
    procedural approach.

  PROCEDURAL VS OBJECT-ORIENTED USAGE

    Depending on your preference, this module can be used a set of
    procedural subroutine calls, or as method calls upon Data::Stag objects,
    or both.

    In procedural mode, all the subroutine calls are prefixed "stag_" to
    avoid namespace clashes. The following three calls are equivalent:

      $person = stag_find($doc, "person");
      $person = $doc->find("person");
      $person = $doc->find_person;

    In object mode, you can treat any tree element as if it is an object
    with automatically defined methods for getting/setting the tag values.

  USE OF XML

    Nested arrays can be imported and exported as XML, as well as other
    formats. XML can be slurped into memory all at once (using less memory
    than an equivalent DOM tree), or a simplified SAX style event handling
    model can be used. Similarly, data can be exported all at once, or as a
    series of events.

    Although this module can be used as a general XML tool, it is intended
    primarily as a tool for manipulating hierarchical data using nested
    tag/value pairs.

    By using a simpler subset of XML equivalent to a basic data tree
    structure, we can write simpler, cleaner code. This simplicity comes at
    a price - this module is not very suitable for XML with attributes or
    mixed content.

    All attributes are turned into elements. This means that it will not
    round-trip a piece of xml with attributes in it. For some applications
    this is acceptable, for others it is not.

    Mixed content cannot be represented in a simple tree format, so this is
    also expanded.

    The following piece of XML

      <paragraph id="1">
        example of <bold>mixed</bold>content
      </paragraph>

    gets parsed as if it were actually:

      <paragraph>
        <paragraph-id>1</paragraph-id>
        <paragraph-text>example of</paragraph-text>
        <bold>mixed</bold>
        <paragraph-text>content</paragraph-text>
      </paragraph>

    This module is more suited to dealing with data-oriented documents than
    text-oriented documents.

    It can also be used as part of a SAX-style event generation / handling
    framework - see the Data::Stag::BaseHandler manpage

    Because nested arrays are native to perl, we can specify an XML
    datastructure directly in perl without going through multiple object
    calls.

    For example, instead of the lengthy

      $obj->startTag("record");
      $obj->startTag("field1");
      $obj->characters("foo");
      $obj->endTag("field1");
      $obj->startTag("field2");
      $obj->characters("bar");
      $obj->endTag("field2");
      $obj->end("record");

    We can instead write

      $struct = [ record => [
                  [ field1 => 'foo'],
                  [ field2 => 'bar']]];

   PARSING

    The following example is for parsing out subsections of a tree and
    changing sub-elements

      use Data::Stag qw(:all);
      my $tree = stag_parse($xmlfile);
      my ($subtree) = stag_findnode($tree, $element);
      stag_set($element, $sub_element, $new_val);
      print stag_xml($subtree);

   OBJECT ORIENTED

    The same can be done in a more OO fashion

      use Data::Stag qw(:all);
      my $tree = Data::Stag->parse($xmlfile);
      my ($subtree) = $tree->findnode($element);
      $element->set($sub_element, $new_val);
      print $subtree->xml;

   IN A STREAM

    Rather than parsing in a whole file into memory all at once (which may
    not be suitable for very large files), you can take an event handling
    approach. The easiest way to do this to register which nodes in the file
    you are interested in using the makehandler method. The parser will
    sweep through the file, building objects as it goes, and handing the
    object to a subroutine that you specify.

    For example:

      use Data::Stag;
      # catch the end of 'person' elements
      my $h = Data::Stag->makehandler( person=> sub {
                                                   my ($self, $person) = @_;
                                                   printf "name:%s phone:%s\n",
                                                     $person->get_name,
                                                     $person->get_phone;
                                                   return;   # clear node
                                                    });
      Data::Stag->parse(-handler=>$h,
                        -file=>$f);

    see the Data::Stag::BaseHandler manpage for writing handlers

    See the Stag website at http://stag.sourceforge.net for more examples.

  STRUCTURED TAGS TREE DATA STRUCTURE

    A tree of structured tags is represented as a recursively nested array,
    the elements of the array represent nodes in the tree.

    A node is a name/data pair, that can represent tags and values. A node
    is represented using a reference to an array, where the first element of
    the array is the tagname, or element, and the second element is the data

    This can be visualised as a box:

      +-----------+
      |Name | Data|
      +-----------+

    In perl, we represent this pair as a reference to an array

      [ Name => $Data ]

    The Data can either be a list of child nodes (subtrees), or a data
    value.

    The terminal nodes (leafs of the tree) contain data values; this is
    represented in perl using primitive scalars.

    For example:

      [ Name => 'Fred' ]

    For non-terminal nodes, the Data is a reference to an array, where each
    element of the the array is a new node.

      +-----------+
      |Name | Data|
      +-----------+
              |||   +-----------+
              ||+-->|Name | Data|
              ||    +-----------+
              ||    
              ||    +-----------+
              |+--->|Name | Data|
              |     +-----------+
              |     
              |     +-----------+
              +---->|Name | Data|
                    +-----------+

    In perl this would be:

      [ Name => [
                  [Name1 => $Data1],
                  [Name2 => $Data2],
                  [Name3 => $Data3],
                ]
      ];

    The extra level of nesting is required to be able to store any node in
    the tree using a single variable. This representation has lots of
    advantages over others, eg hashes and mixed hash/array structures.

  MANIPULATION AND QUERYING

    The following example is taken from biology; we have a list of species
    (mouse, human, fly) and a list of genes found in that species. These are
    cross-referenced by an identifier called tax_id. We can do a
    relational-style inner join on this identifier, as follows -

      use Data::Stag qw(:all);
      my $tree =
      Data::Stag->new(
        'db' => [
        [ 'species_set' => [
          [ 'species' => [
            [ 'common_name' => 'house mouse' ],
            [ 'binomial' => 'Mus musculus' ],
            [ 'tax_id' => '10090' ]]],
          [ 'species' => [
            [ 'common_name' => 'fruit fly' ],
            [ 'binomial' => 'Drosophila melanogaster' ],
            [ 'tax_id' => '7227' ]]],
          [ 'species' => [
            [ 'common_name' => 'human' ],
            [ 'binomial' => 'Homo sapiens' ],
            [ 'tax_id' => '9606' ]]]]],
        [ 'gene_set' => [
          [ 'gene' => [
            [ 'symbol' => 'HGNC' ],
            [ 'tax_id' => '9606' ],
            [ 'phenotype' => 'Hemochromatosis' ],
            [ 'phenotype' => 'Porphyria variegata' ],
            [ 'GO_term' => 'iron homeostasis' ],
            [ 'map' => '6p21.3' ]]],
          [ 'gene' => [
            [ 'symbol' => 'Hfe' ],
            [ 'synonym' => 'MR2' ],
            [ 'tax_id' => '10090' ],
            [ 'GO_term' => 'integral membrane protein' ],
            [ 'map' => '13 A2-A4' ]]]]]]
       );

      # inner join of species and gene parts of tree,
      # based on 'tax_id' element
      my $gene_set = $tree->find("gene_set");       # get <gene_set> element
      my $species_set = $tree->find("species_set"); # get <species_set> element
      $gene_set->ijoin("gene", "tax_id", $species_set);   # INNER JOIN

      print "Reorganised data:\n";
      print $gene_set->xml;

      # find all genes starting with letter 'H' in where species/common_name=human
      my @genes =
        $gene_set->where('gene',
                         sub { my $g = shift;
                               $g->get_symbol =~ /^H/ &&
                               $g->findval("common_name") eq ('human')});

      print "Human genes beginning 'H'\n";
      print $_->xml foreach @genes;

  S-Expression (Lisp) representation

    The data represented using this module can be represented as Lisp-style
    S-Expressions.

    See the Data::Stag::SxprParser manpage and the Data::Stag::SxprWriter
    manpage

    If we execute this code on the XML from the example above

      $stag = Data::Stag->parse($xmlfile);
      print $stag->sxpr;

    The following S-Expression will be printed:

      '(db
        (species_set
          (species
            (common_name "house mouse")
            (binomial "Mus musculus")
            (tax_id "10090"))
          (species
            (common_name "fruit fly")
            (binomial "Drosophila melanogaster")
            (tax_id "7227"))
          (species
            (common_name "human")
            (binomial "Homo sapiens")
            (tax_id "9606")))
        (gene_set
          (gene
            (symbol "HGNC")
            (tax_id "9606")
            (phenotype "Hemochromatosis")
            (phenotype "Porphyria variegata")
            (GO_term "iron homeostasis")
            (map
              (cytological
                (chromosome "6")
                (band "p21.3"))))
          (gene
            (symbol "Hfe")
            (synonym "MR2")
            (tax_id "10090")
            (GO_term "integral membrane protein")))
        (similarity_set
          (pair
            (symbol "HGNC")
            (symbol "Hfe"))
          (pair
            (symbol "WNT3A")
            (symbol "Wnt3a"))))

   TIPS FOR EMACS USERS AND LISP PROGRAMMERS

    If you use emacs, you can save this as a file with the ".el" suffix and
    get syntax highlighting for editing this file. Quotes around the
    terminal node data items are optional.

    If you know emacs lisp or any other lisp, this also turns out to be a
    very nice language for manipulating these datastructures. Try copying
    and pasting the above s-expression to the emacs scratch buffer and
    playing with it in lisp.

  INDENTED TEXT REPRESENTATION

    Data::Stag has its own text format for writing data trees. Again, this
    is only possible because we are working with a subset of XML (no
    attributes, no mixed elements). The data structure above can be written
    as follows -

      db:
        species_set:
          species:
            common_name: house mouse
            binomial: Mus musculus
            tax_id: 10090
          species:
            common_name: fruit fly
            binomial: Drosophila melanogaster
            tax_id: 7227
          species:
            common_name: human
            binomial: Homo sapiens
            tax_id: 9606
        gene_set:
          gene:
            symbol: HGNC
            tax_id: 9606
            phenotype: Hemochromatosis
            phenotype: Porphyria variegata
            GO_term: iron homeostasis
            map: 6p21.3
          gene:
            symbol: Hfe
            synonym: MR2
            tax_id: 10090
            GO_term: integral membrane protein
            map: 13 A2-A4
        similarity_set:
          pair:
            symbol: HGNC
            symbol: Hfe
          pair:
            symbol: WNT3A
            symbol: Wnt3a

    See the Data::Stag::ITextParser manpage and the Data::Stag::ITextWriter
    manpage

  NESTED ARRAY SPECIFICATION II

    To avoid excessive square bracket usage, you can specify a structure
    like this:

      use Data::Stag qw(:all);
  
      *N = \&stag_new;
      my $tree =
        N(top=>[
                N('personset'=>[
                                N('person'=>[
                                             N('name'=>'davey'),
                                             N('address'=>'here'),
                                             N('description'=>[
                                                               N('hair'=>'green'),
                                                               N('eyes'=>'two'),
                                                               N('teeth'=>5),
                                                              ]
                                              ),
                                             N('pets'=>[
                                                        N('petname'=>'igor'),
                                                        N('petname'=>'ginger'),
                                                       ]
                                              ),
                                                                          
                                            ],
                                 ),
                                N('person'=>[
                                             N('name'=>'shuggy'),
                                             N('address'=>'there'),
                                             N('description'=>[
                                                               N('hair'=>'red'),
                                                               N('eyes'=>'three'),
                                                               N('teeth'=>1),
                                                              ]
                                              ),
                                             N('pets'=>[
                                                        N('petname'=>'thud'),
                                                        N('petname'=>'spud'),
                                                       ]
                                              ),
                                            ]
                                 ),
                               ]
                 ),
                N('animalset'=>[
                                N('animal'=>[
                                             N('name'=>'igor'),
                                             N('class'=>'rat'),
                                             N('description'=>[
                                                               N('fur'=>'white'),
                                                               N('eyes'=>'red'),
                                                               N('teeth'=>50),
                                                              ],
                                              ),
                                            ],
                                 ),
                               ]
                 ),

               ]
         );

      # find all people
      my @persons = stag_find($tree, 'person');

      # write xml for all red haired people
      foreach my $p (@persons) {
        print stag_xml($p)
          if stag_tmatch($p, "hair", "red");
      } ;

      # find all people that have name == shuggy
      my @p =
        stag_qmatch($tree, 
                    "person",
                    "name",
                    "shuggy");

NODES AS DATA OBJECTS
    As well as the methods listed below, a node can be treated as if it is a
    data object of a class determined by the element.

    For example, the following are equivalent.

      $node->get_name;
      $node->get('name');

      $node->set_name('fred');
      $node->set('name', 'fred');

    This is really just syntactic sugar. The autoloaded methods are not
    checked against any schema, although this may be added in future.

STAG METHODS
    All method calls are also available as procedural subroutine calls;
    unless otherwise noted, the subroutine call is the same as the method
    call, but with the string stag_ prefixed to the method name. The first
    argument should be a Data::Stag datastructure.

    To import all subroutines into the current namespace, use this idiom:

      use Data::Stag qw(:all);
      $doc = stag_parse($file);
      @persons = stag_find($doc, 'person');

    If you wish to use this module procedurally, and you are too lazy to
    prefix all calls with stag_, use this idiom:

      use Data::Stag qw(:lazy);
      $doc = parse($file);
      @persons = find($doc, 'person');

    But beware of clashes!

    Most method calls also have a handy short mnemonic. Use of these is
    optional. Software engineering types prefer longer names, in the belief
    that this leads to clearer code. Hacker types prefer shorter names, as
    this requires less keystrokes, and leads to a more compact
    representation of the code. It is expected that if you do use this
    module, then its usage will be fairly ubiquitous within your code, and
    the mnemonics will become familiar, much like the qw and s/ operators in
    perl. As always with perl, the decision is yours.

    Some methods take a single parameter or list of parameters; some have
    large lists of parameters that can be passed in any order. If the
    documentation states:

      Args: [x str], [y int], [z ANY]

    Then the method can be called like this:

      $stag->foo("this is x", 55, $ref);

    or like this:

      $stag->foo(-z=>$ref, -x=>"this is x", -y=>55);

  INITIALIZATION METHODS

   new

           Title: new

            Args: element str, data STAG-DATA
         Returns: Data::Stag node
         Example: $node = stag_new();
         Example: $node = Data::Stag->new;
         Example: $node = Data::Stag->new(person => [[name=>$n], [phone=>$p]]);

    creates a new instance of a Data::Stag node

   stagify (nodify)

           Title: stagify
         Synonym: nodify
            Args: data ARRAY-REF
         Returns: Data::Stag node
         Example: $node = stag_stagify([person => [[name=>$n], [phone=>$p]]]);

    turns a perl array reference into a Data::Stag node.

    similar to new

   parse

           Title: parse

            Args: [file str], [format str], [handler obj], [fh FileHandle]
         Returns: Data::Stag node
         Example: $node = stag_parse($fn);
         Example: $node = stag_parse(-fh=>$fh, -handler=>$h, -errhandler=>$eh);
         Example: $node = Data::Stag->parse(-file=>$fn, -handler=>$myhandler);

    slurps a file or string into a Data::Stag node structure. Will guess the
    format (xml, sxpr, itext) from the suffix if it is not given.

    The format can also be the name of a parsing module, or an actual parser
    object;

    The handler is any object that can take nested Stag events (start_event,
    end_event, evbody) which are generated from the parse. If the handler is
    omitted, all events will be cached and the resulting tree will be
    returned.

    See the Data::Stag::BaseHandler manpage for writing your own handlers

    See the Data::Stag::BaseGenerator manpage for details on parser classes,
    and error handling

   parsestr

           Title: parsestr

            Args: [str str], [format str], [handler obj]
         Returns: Data::Stag node
         Example: $node = stag_parsestr('(a (b (c "1")))');
         Example: $node = Data::Stag->parsestr(-str=>$str, -handler=>$myhandler);

    Similar to parse(), except the first argument is a string

   from

           Title: from

            Args: format str, source str
         Returns: Data::Stag node
         Example: $node = stag_from('xml', $fn);
         Example: $node = stag_from('xmlstr', q[<top><x>1</x></top>]);
         Example: $node = Data::Stag->from($parser, $fn);

    Similar to parse

    slurps a file or string into a Data::Stag node structure.

    The format can also be the name of a parsing module, or an actual parser
    object

   unflatten

           Title: unflatten

            Args: data array
         Returns: Data::Stag node
         Example: $node = stag_unflatten(person=>[name=>$n, phone=>$p, address=>[street=>$s, city=>$c]]);

    Creates a node structure from a semi-flattened representation, in which
    children of a node are represented as a flat list of data rather than a
    list of array references.

    This means a structure can be specified as:

      person=>[name=>$n,
               phone=>$p, 
               address=>[street=>$s, 
                         city=>$c]]

    Instead of:

      [person=>[ [name=>$n],
                 [phone=>$p], 
                 [address=>[ [street=>$s], 
                             [city=>$c] ] ]
               ]
      ]

    The former gets converted into the latter for the internal
    representation

   makehandler

           Title: makehandler

            Args: hash of CODEREFs keyed by element name
                  OR a string containing the name of a module
         Returns: L<Data::Stag::BaseHandler>
         Example: $h = Data::Stag->makehandler(%subs);
         Example: $h = Data::Stag->makehandler("My::FooHandler");

    This creates a Stag event handler. The argument is a hash of subroutines
    keyed by element/node name. After each node is fired by the
    parser/generator, the subroutine is called, passing the handler object
    and the stag node as arguments. whatever the subroutine returns is
    placed back into the tree

    For example, for a a parser/generator that fires events with the
    following tree form

      <person>
        <name>foo</name>
        ...
      </person>

    we can create a handler that writes person/name like this:

      $h = Data::Stag->makehandler(
                                   person => sub { my ($self,$stag) = @_;
                                                   print $stag->name;
                                                   return $stag; # dont change tree
                                                 });
      $stag = Data::Stag->parse(-str=>"(...)", -handler=>$h)

    See the Data::Stag::BaseHandler manpage for details on handlers

   getformathandler

           Title: getformathandler

            Args: format str OR L<Data::Stag::BaseHandler>
         Returns: L<Data::Stag::BaseHandler>
         Example: $h = Data::Stag->getformathandler('xml');
                  $h->file("my.xml");
                  Data::Stag->parse(-fn=>$fn, -handler=>$h);

    Creates a Stag event handler - this handler can be passed to an event
    generator / parser. Built in handlers include:

    xml Generates xml tags from events

    sxpr
        Generates S-Expressions from events

    itext
        Generates indented text from events

    All the above are kinds of the Data::Stag::Writer manpage

   chainhandler

           Title: chainhandler

            Args: blocked events - str or str[]
                  initial handler - handler object
                  final handler - handler object
         Returns: 
         Example: $h = Data::Stag->chainhandler('foo', $processor, 'xml')

    chains handlers together - for example, you may want to make transforms
    on an event stream, and then pass the event stream to another handler -
    for example, and xml handler

      $processor = Data::Stag->makehandler(
                                           a => sub { my ($self,$stag) = @_;
                                                      $stag->set_foo("bar");
                                                      return $stag
                                                    },
                                           b => sub { my ($self,$stag) = @_;
                                                      $stag->set_blah("eek");
                                                      return $stag
                                                    },
                                           );
      $chainh = Data::Stag->chainhandler(['a', 'b'], $processor, 'xml');
      $stag = Data::Stag->parse(-str=>"(...)", -handler=>$chainh)

    chains together two handlers (see also the script stag-handle.pl)

  RECURSIVE SEARCHING

   find (f)

           Title: find
         Synonym: f

            Args: element str
         Returns: node[] or ANY
         Example: @persons = stag_find($struct, 'person');
         Example: @persons = $struct->find('person');

    recursively searches tree for all elements of the given type, and
    returns all nodes or data elements found.

    if the element found is a non-terminal node, will return the node if the
    element found is a terminal (leaf) node, will return the data value

    the element argument can be a path

      @names = $struct->find('department/person/name');

    will find name in the nested structure below:

      (department
       (person
        (name "foo")))

   findnode (fn)

           Title: findnode
         Synonym: fn

            Args: element str
         Returns: node[]
         Example: @persons = stag_findnode($struct, 'person');
         Example: @persons = $struct->findnode('person');

    recursively searches tree for all elements of the given type, and
    returns all nodes found.

    paths can also be used (see find)

   findval (fv)

           Title: findval
         Synonym: fv

            Args: element str
         Returns: ANY[] or ANY
         Example: @names = stag_findval($struct, 'name');
         Example: @names = $struct->findval('name');
         Example: $firstname = $struct->findval('name');

    recursively searches tree for all elements of the given type, and
    returns all data values found. the data values could be primitive
    scalars or nodes.

    paths can also be used (see find)

   sfindval (sfv)

           Title: sfindval
         Synonym: sfv

            Args: element str
         Returns: ANY
         Example: $name = stag_sfindval($struct, 'name');
         Example: $name = $struct->sfindval('name');

    as findval, but returns the first value found

    paths can also be used (see find)

   findvallist (fvl)

           Title: findvallist
         Synonym: fvl

            Args: element str[]
         Returns: ANY[]
         Example: ($name, $phone) = stag_findvallist($personstruct, 'name', 'phone');
         Example: ($name, $phone) = $personstruct->findvallist('name', 'phone');

    recursively searches tree for all elements in the list

    DEPRECATED

  DATA ACCESSOR METHODS

    these allow getting and setting of elements directly underneath the
    current one

   get (g)

           Title: get
         Synonym: g

            Args: element str
          Return: node[] or ANY
         Example: $name = $person->get('name');
         Example: @phone_nos = $person->get('phone_no');

    gets the value of the named sub-element

    if the sub-element is a non-terminal, will return a node(s) if the
    sub-element is a terminal (leaf) it will return the data value(s)

    the examples above would work on a data structure like this:

      [person => [ [name => 'fred'],
                   [phone_no => '1-800-111-2222'],
                   [phone_no => '1-415-555-5555']]]

    will return an array or single value depending on the context

    [equivalent to findval(), except that only direct children (as opposed
    to all descendents) are checked]

    paths can also be used, like this:

     @phones_nos = $struct->get('person/phone_no')

   sget (sg)

           Title: sget
         Synonym: sg

            Args: element str
          Return: ANY
         Example: $name = $person->sget('name');
         Example: $phone = $person->sget('phone_no');
         Example: $phone = $person->sget('department/person/name');

    as get but always returns a single value

    [equivalent to sfindval(), except that only direct children (as opposed
    to all descendents) are checked]

   getl (gl getlist)

           Title: gl
         Synonym: getl
         Synonym: getlist

            Args: element str[]
          Return: node[] or ANY[]
         Example: ($name, @phone) = $person->getl('name', 'phone_no');

    returns the data values for a list of sub-elements of a node

    [equivalent to findvallist(), except that only direct children (as
    opposed to all descendents) are checked]

   getn (gn getnode)

           Title: getn
         Synonym: gn
         Synonym: getnode

            Args: element str
          Return: node[]
         Example: $namestruct = $person->getn('name');
         Example: @pstructs = $person->getn('phone_no');

    as get but returns the whole node rather than just the data value

    [equivalent to findnode(), except that only direct children (as opposed
    to all descendents) are checked]

   sgetmap (sgm)

           Title: sgetmap
         Synonym: sgm

            Args: hash
          Return: hash
         Example: %h = $person->sgetmap('social-security-no'=>'id', 
                                        'name'              =>'label',
                                        'job'               =>0,
                                        'address'           =>'location');

    returns a hash of key/val pairs based on the values of the data values
    of the subnodes in the current element; keys are mapped according to the
    hash passed (a value of '' or 0 will map an identical key/val).

    no multivalued data elements are allowed

   set (s)

           Title: set
         Synonym: s

            Args: element str, datavalue ANY (list)
          Return: ANY
         Example: $person->set('name', 'fred');    # single val
         Example: $person->set('phone_no', $cellphone, $homephone);

    sets the data value of an element for any node. if the element is
    multivalued, all the old values will be replaced with the new ones
    specified.

    ordering will be preserved, unless the element specified does not exist,
    in which case, the new tag/value pair will be placed at the end.

    for example, if we have a stag node $person

      person:
        name: shuggy
        job:  bus driver

    if we do this

      $person->set('name', ());

    we will end up with

      person:
        job:  bus driver

    then if we do this

      $person->set('name', 'shuggy');

    the 'name' node will be placed as the last attribute

      person:
        job:  bus driver
        name: shuggy

    You can also use magic methods, for example

      $person->set_name('shuggy');
      $person->set_job('bus driver', 'poet');
      print $person->itext;

    will print

      person:
        name: shuggy
        job:  bus driver
        job:  poet

    note that if the datavalue is a non-terminal node as opposed to a
    primitive value, then you have to do it like this:

      $people  = Data::Stag->new(people=>[
                                          [person=>[[name=>'Sherlock Holmes']]],
                                          [person=>[[name=>'Moriarty']]],
                                         ]);
      $address = Data::Stag->new(address=>[
                                           [address_line=>"221B Baker Street"],
                                           [city=>"London"],
                                           [country=>"Great Britain"]]);
      ($person) = $people->qmatch('person', (name => "Sherlock Holmes"));
      $person->set("address", $address->data);

   unset (u)

           Title: unset
         Synonym: u

            Args: element str, datavalue ANY
          Return: ANY
         Example: $person->unset('name');
         Example: $person->unset('phone_no');

    prunes all nodes of the specified element from the current node

    You can use magic methods, like this

      $person->unset_name;
      $person->unset_phone_no;

   free

           Title: free
         Synonym: u

            Args: 
          Return: 
         Example: $person->free;

    removes all data from a node. If that node is a subnode of another node,
    it is removed altogether

    for instance, if we had the data below:

      <person>
        <name>fred</name>
        <address>
        ..
        </address>
      </person>

    and called

      $person->get_address->free

    then the person node would look like this:

      <person>
        <name>fred</name>
      </person>

   add (a)

           Title: add
         Synonym: a

            Args: element str, datavalues ANY[]
                  OR
                  Data::Stag
          Return: ANY
         Example: $person->add('phone_no', $cellphone, $homephone);
         Example: $person->add_phone_no('1-555-555-5555');
         Example: $dataset->add($person)

    adds a datavalue or list of datavalues. appends if already existing,
    creates new element value pairs if not already existing.

    if the argument is a stag node, it will add this node under the current
    one

   element (e name)

           Title: element
         Synonym: e
         Synonym: name

            Args:
          Return: element str
         Example: $element = $struct->element

    returns the element name of the current node.

    This is illustrated in the different representation formats below

    sxpr
          (element "data")

        or

          (element
           (sub_element "..."))

    xml
          <element>data</element>

        or

          <element>
            <sub_element>...</sub_element>
          </element>

    perl
          [element => $data ]

        or

          [element => [
                        [sub_element => "..." ]]]

    itext
          element: data

        or

          element:
            sub_element: ...

   kids (k children)

           Title: kids
         Synonym: k
         Synonym: children

            Args:
          Return: ANY or ANY[]
         Example: @nodes = $person->kids
         Example: $name = $namestruct->kids

    returns the data value(s) of the current node; if it is a terminal node,
    returns a single value which is the data. if it is non-terminal, returns
    an array of nodes

   addkid (ak addchild)

           Title: addkid
         Synonym: ak
         Synonym: addchild

            Args: kid node
          Return: ANY
         Example: $person->addkid('job', $job);

    adds a new child node to a non-terminal node, after all the existing
    child nodes

   subnodes

           Title: subnodes

            Args: 
          Return: ANY[]
         Example: @nodes = $person->subnodes

    returns the non-terminal data value(s) of the current node;

  QUERYING AND ADVANCED DATA MANIPULATION

   ijoin (j)

           Title: ijoin
         Synonym: j
         Synonym: ij

            Args: element str, key str, data Node
          Return: undef

    does a relational style inner join - see previous example in this doc

    key can either be a single node name that must be shared (analagous to
    SQL INNER JOIN .. USING), or a key1=key2 equivalence relation (analagous
    to SQL INNER JOIN ... ON)

   qmatch (qm)

           Title: qmatch
         Synonym: qm

            Args: return-element str, match-element str, match-value str
          Return: node[]
         Example: @persons = $s->qmatch('person', 'name', 'fred');
         Example: @persons = $s->qmatch('person', (job=>'bus driver'));

    queries the node tree for all elements that satisfy the specified
    key=val match - see previous example in this doc

    for those inclined to thinking relationally, this can be thought of as a
    query that returns a stag object:

      SELECT <return-element> FROM <stag-node> WHERE <match-element> = <match-value>

    this always returns an array; this means that calling in a scalar
    context will return the number of elements; for example

      $n = $s->qmatch('person', (name=>'fred'));

    the value of $n will be equal to the number of persons called fred

   tmatch (tm)

           Title: tmatch
         Synonym: tm

            Args: element str, value str
          Return: bool
         Example: @persons = grep {$_->tmatch('name', 'fred')} @persons

    returns true if the the value of the specified element matches - see
    previous example in this doc

   tmatchhash (tmh)

           Title: tmatchhash
         Synonym: tmh

            Args: match hashref
          Return: bool
         Example: @persons = grep {$_->tmatchhash({name=>'fred', hair_colour=>'green'})} @persons

    returns true if the node matches a set of constraints, specified as
    hash.

   tmatchnode (tmn)

           Title: tmatchnode
         Synonym: tmn

            Args: match node
          Return: bool
         Example: @persons = grep {$_->tmatchnode([person=>[[name=>'fred'], [hair_colour=>'green']]])} @persons

    returns true if the node matches a set of constraints, specified as node

   cmatch (cm)

           Title: cmatch
         Synonym: cm

            Args: element str, value str
          Return: bool
         Example: $n_freds = $personset->cmatch('name', 'fred');

    counts the number of matches

   where (w)

           Title: where
         Synonym: w

            Args: element str, test CODE
          Return: Node[]
         Example: @rich_persons = $data->where('person', sub {shift->get_salary > 100000});

    the tree is queried for all elements of the specified type that satisfy
    the coderef (must return a boolean)

      my @rich_dog_or_cat_owners =
        $data->where('person',
                     sub {my $p = shift;
                          $p->get_salary > 100000 &&
                          $p->where('pet',
                                    sub {shift->get_type =~ /(dog|cat)/})});

   iterate (i)

           Title: iterate
         Synonym: i

            Args: CODE
          Return: Node[]
         Example: $data->iterate(sub {
                                     my $stag = shift;
                                     my $parent = shift;
                                     if ($stag->element eq 'pet') {
                                         $parent->set_pet_name($stag->get_name);
                                     }
                                 });

    iterates through whole tree calling the specified subroutine.

    the first arg passed to the subroutine is the stag node representing the
    tree at that point; the second arg is for the parent.

    for instance, the example code above would turn this

      (person
       (name "jim")
       (pet
        (name "fluffy")))

    into this

      (person
       (name "jim")
       (pet_name "fluffy")
       (pet
        (name "fluffy")))

  MISCELLANEOUS METHODS

   duplicate (d)

           Title: duplicate
         Synonym: d

            Args:
          Return: Node
         Example: $node2 = $node->duplicate;

    does a deep copy of a stag structure

   isanode

           Title: isanode

            Args:
          Return: bool
         Example: if (stag_isanode($node)) { ... }

   hash

           Title: hash

            Args:
          Return: hash
         Example: $h = $node->hash;

    turns a tree into a hash. all data values will be arrayrefs

   pairs

           Title: pairs

    turns a tree into a hash. all data values will be scalar (IMPORTANT:
    this means duplicate values will be lost)

   write

           Title: write

            Args: filename str, format str[optional]
          Return:
         Example: $node->write("myfile.xml");
         Example: $node->write("myfile", "itext");

    will try and guess the format from the extension if not specified

   xml

           Title: xml

            Args: filename str, format str[optional]
          Return:
         Example: $node->write("myfile.xml");
         Example: $node->write("myfile", "itext");

            Args:
          Return: xml str
         Example: print $node->xml;

  XML METHODS

   sax

           Title: sax

            Args: saxhandler SAX-CLASS
          Return:
         Example: $node->sax($mysaxhandler);

    turns a tree into a series of SAX events

   xpath (xp tree2xpath)

           Title: xpath
         Synonym: xp
         Synonym: tree2xpath

            Args:
          Return: xpath object
         Example: $xp = $node->xpath; $q = $xp->find($xpathquerystr);

   xpquery (xpq xpathquery)

           Title: xpquery
         Synonym: xpq
         Synonym: xpathquery

            Args: xpathquery str
          Return: Node[]
         Example: @nodes = $node->xqp($xpathquerystr);

STAG SCRIPTS
    The following scripts come with the stag module

    stag-autoschema.pl
        writes the implicit stag-schema for a stag file

    stag-db.pl
        persistent storage and retrieval for stag data (xml, sxpr, itext)

    stag-diff.pl
        finds the difference between two stag files

    stag-drawtree.pl
        draws a stag file (xml, itext, sxpr) as a PNG diagram

    stag-filter.pl
        filters a stag file (xml, itext, sxpr) for nodes of interest

    stag-findsubtree.pl
        finds nodes in a stag file

    stag-flatten.pl
        turns stag data into a flat table

    stag-grep.pl
        filters a stag file (xml, itext, sxpr) for nodes of interest

    stag-handle.pl
        streams a stag file through a handler into a writer

    stag-join.pl
        joins two stag files together based around common key

    stag-mogrify.pl
        mangle stag files

    stag-parse.pl
        parses a file and fires events (e.g. sxpr to xml)

    stag-query.pl
        aggregare queries

    stag-split.pl
        splits a stag file (xml, itext, sxpr) into multiple files

    stag-splitter.pl
        splits a stag file into multiple files

    stag-view.pl
        draws an expandable Tk tree diagram showing stag data

    To get more documentation, type

      stag_<script> -h

BUGS
    none known so far, possibly quite a few undocumented features!

    Not a bug, but the underlying default datastructure of nested arrays is
    more heavyweight than it needs to be. More lightweight implementations
    are possible. Some time I will write a C implementation.

WEBSITE
    http://stag.sourceforge.net

WEBSITE
    http://stag.sourceforge.net

AUTHOR
    Chris Mungall <cjm AT fruitfly DOT org>

COPYRIGHT
    Copyright (c) 2004 Chris Mungall

    This module is free software. You may distribute this module under the
    same terms as perl itself