PHP - Extracting Data From Particular Attribute Using Simplexml

good evening dear php-freaks, 

hope you are all right. 

i am currently working on a parser that gets  data via OSM Overpass API with PHP-SimpleXML. I am workin with the pretty new to the work with PHPSimpleXML so do not bear with me for askin newby questions.  I am tryin to get data using Open Street Maps. I want to write a code that works with the endpoint of openstreetmap - and the given data is the starting point for further explorations.

My tactic is as follows:

 
I fetch data from the openstreetmap-endpoint 

1. i run requests to the openstreetmap-endpoint- (see below) and i try three different APIs per request isn't that easy on ressources and 

2. I don't know how to work with the results that i gather from the OpenStreetmap-Endpoint

as of the first point:  - workin on the endpoint of  OSM-Overpass-API.... see my approach: 

<?php
/**
 * OSM Overpass API with PHP SimpleXML / XPath
 *
 * PHP Version: 5.4 - Can be back-ported to 5.3 by using 5.3 Array-Syntax (not PHP 5.4's square brackets)
 */
//
// 1.) Query an OSM Overpass API Endpoint
//

$query = 'node
  ["amenity"~".*"]
  (38.415938460513274,16.06338500976562,39.52205163048525,17.51220703125);
out;';

$context = stream_context_create(['http' => [
    'method'  => 'POST',
    'header' => ['Content-Type: application/x-www-form-urlencoded'],
    'content' => 'data=' . urlencode($query),
]]);

# please do not stress this service, this example is for demonstration purposes only.
$endpoint = 'http://overpass-api.de/api/interpreter';
libxml_set_streams_context($context);
$start = microtime(true);

$result = simplexml_load_file($endpoint);
printf("Query returned %2\$d node(s) and took %1\$.5f seconds.\n\n", microtime(true) - $start, count($result->node));

//
// 2.) Work with the XML Result
//

so far so good:  with this i get a bunch of data..... 

I have data in a file retrieved from a API pull request at the openstreetmap data source that looks something like this:

<?xml version="1.0" encoding="UTF-8"?>
<osm version="0.6" generator="Osmosis SNAPSHOT-r26564" xapi:planetDate="2014-10-07T15:42:02Z" xmlns:xapi="http://jxapi.openstreetmap.org/">
   <node id="251652819" version="6" timestamp="2013-10-19T14:03:10Z" uid="1198089" user="GeorgeKaplan" changeset="18434238" lat="48.8527413" lon="2.3333559">
     <tag k="dispensing" v="yes"/>
     <tag k="website" v="http://www.pharmacie-paris-citypharma.fr/"/>
     <tag k="name" v="Pharmacie Citypharma in downtown paris"/>
     <tag k="amenity" v="pharmacy"/>
  </node>
  <node id="251774849" version="9" timestamp="2014-07-28T21:28:26Z" uid="92075" user="Art Penteur" changeset="24411346" lat="48.8468043" lon="2.3696423">
     <tag k="phone" v="0143430996"/>
     <tag k="dispensing" v="yes"/>
     <tag k="name" v="Pharmacie de la Rapée in downtown paris"/>
     <tag k="amenity" v="pharmacy"/>
     <tag k="opening_hours" v="Mo-Fr 08:30-20:30; Sa 09:00-19:30"/>
 </node>
 <node id="263262912" version="3" timestamp="2014-07-28T21:37:24Z" uid="92075" user="Art Penteur" changeset="24411346" lat="48.8446917" lon="2.3101829">
     <tag k="dispensing" v="yes"/>
     <tag k="amenity" v="pharmacy"/>
 </node>

and so forth and so forth ....etc.

what is aimed: I am trying to filter the records based on the attributes that i find in the dataset,
 basically i am trying to retrieve the records that do not have a

    <tag k="name" v="blahblahblah"/> field.

I have been looking around and the classical way to do it its easy, however because of my poor skills in doing anything 
xml related i do have a couple of questions:

Is it possible to apply xml filtering for tags that look like this

<tag k="dispensing" v="yes"/> 

ones that do not have the

 <tag></tag>

.....format. Also how can i filter the records when each child of the node has different attributes,like v, 
i would knew how to do it if it would look like this

  <tag k="name">Pharmacie in Paris-downtown -  Rapée-metro-station</tag> 

but within this format received at this moment i cannot  not see a way out on how to get the children that i need

i have had a quick look at the PHP-SimpleXML and the XPath-approach: it may help me in achieving what is aimed.

but at the moment - i think i got stuck. 

i greatly appreciated hints and some ideas that may fit her. 

have a great day. -  yours dil_bert