Cannot open self-created sdlxliff file on SDL Trados 2015

I'm a developer. I have created an .sdlxliff file by myself, based on the XLIFF 1.2 Standard. (Source: en.wikipedia.org/.../XLIFF). It's essentially an .xml file, so I save it as xml with the extension ".sdlxliff". But I can't open it with Trados 2015, even if I created a same file as the example in the forementioned Wikipedia page. Like this:

<xliff version="1.2">
 <file original="Graphic Example.psd"
  source-language="en-US" target-language="ja-JP"
  tool="Rainbow" datatype="photoshop">
  <header>
   <skl>
    <external-file uid="3BB236513BB24732" href="Graphic Example.psd.skl"/>
   </skl>
   <phase-group>
    <phase phase-name="extract" process-name="extraction"
     tool="Rainbow" date="20010926T152258Z"
     company-name="NeverLand Inc." job-id="123"
     contact-name="Peter Pan" contact-email="ppan@example.com">
     <note>Make sure to use the glossary I sent you yesterday.
      Thanks.</note>
    </phase>
   </phase-group>
  </header>
  <body>
   <trans-unit id="1" maxbytes="14">
    <source xml:lang="en-US">Quetzal</source>
    <target xml:lang="ja-JP">Quetzal</target>
   </trans-unit>
   <trans-unit id="3" maxbytes="114">
    <source xml:lang="en-US">An application to manipulate and 
     process XLIFF documents</source>
    <target xml:lang="ja-JP">XLIFF 文書を編集、または処理
     するアプリケーションです。</target>
   </trans-unit>
   <trans-unit id="4" maxbytes="36">
    <source xml:lang="en-US">XLIFF Data Manager</source>
    <target xml:lang="ja-JP">XLIFF データ・マネージャ</target>
   </trans-unit>
  </body>
 </file>
</xliff>

It keeps telling me Trados doesn't support such file type. Can anyone tell me why it doesn't work? Might need technical support on this.