XML : Read long xml with php

i have a problem with reading my xml. By code down i read xml, bud how i say at the end of this post, i need read subelements. But i don't know how.

     $reader = new XMLReader();  $reader->open("data/sns.xml");  while($reader->read()){       if ($reader->nodeType == XMLReader::ELEMENT && $reader->name == "item" && $reader->getAttribute('sensor') == "th0" && $reader->getAttribute('cat') == "temp" && $reader->getAttribute('unit') == "c") {                          echo "Venkovní teplota: ".$reader->readString()." °C";                          echo "<br />";                      }                      if($reader->nodeType == XMLReader::ELEMENT && $reader->name == "item" && $reader->getAttribute("sensor") == "th0" && $reader->getAttribute("cat") == "hum" && $reader->getAttribute("unit") == "rel"){                          echo "venkovní vlhkost: ".$reader->readString();                          echo "<br />";                      }}    

I can read this, but my xml looks like:

   <data timeframe="actual">  <item sensor="system" cat="version" unit="text">4.9u</item>  <item sensor="system" cat="version" unit="num">49</item>  <item sensor="system" cat="build" unit="num">1261</item>  <item sensor="system" cat="platform" unit="text">SilverStone_DC01</item>  <item sensor="system" cat="language" unit="text">Czech</item>  <item sensor="system" cat="temp" unit="unit">c</item>  <item sensor="system" cat="hum" unit="unit">rel</item>  <item sensor="system" cat="press" unit="unit">hpa</item>  <item sensor="system" cat="wind" unit="unit">ms</item>  <item sensor="system" cat="rain" unit="unit">mm</item>  <item sensor="date0" cat="date" unit="utc">20160111090606</item>  <item sensor="date0" cat="date2" unit="utc">11.01.2016 09:06:06</item>  <item sensor="date0" cat="puredate" unit="utc">11.01.2016</item>  <item sensor="date0" cat="time" unit="utc">09:06:06</item>  <item sensor="date0" cat="year" unit="utc">2016</item>  <item sensor="date0" cat="month" unit="utc">01</item>  <item sensor="date0" cat="day" unit="utc">11</item>  <item sensor="date0" cat="dayofweek" unit="utc">1</item>  <item sensor="date0" cat="hour" unit="utc">09</item>  <item sensor="date0" cat="min" unit="utc">06</item>  <item sensor="date0" cat="sec" unit="utc">06</item>  <item sensor="date0" cat="date" unit="local">20160111100606</item>  <item sensor="date0" cat="date2" unit="local">11.01.2016 10:06:06</item>  <item sensor="date0" cat="puredate" unit="local">11.01.2016</item>  <item sensor="date0" cat="time" unit="local">10:06:06</item>  <item sensor="date0" cat="year" unit="local">2016</item>  <item sensor="date0" cat="month" unit="local">01</item>  <item sensor="date0" cat="day" unit="local">11</item>  </data>    

and i need read for example. sensor: date0 and cat: date2 and unit: utc and now show me a string.

When you are looking for this code u say it is easy, but in my xml i have next tag

  <data timeframe="lastday"></data>    

and the same items, bud i need to read only actual.

Please help.

Thank You