You're only going to need a diploma for calling yourself stuff like engineer (although that varies by country).
Software engineer = Has diploma
Software developer = Can be anyone
Software guru = Is usually someone who think they're good
<Something> specialist = Usually knows his shit about the subject. (ie. database specialist)
<Something> scientist = These people are hardcore within their subject, and almost everyone has diploma (but afaik not required for the title). It's more of a way you see yourself. (ie. Data scientist).
