الإتاحة: http://www.ssoar.info/ssoar/handle/document/11362http://www.ssoar.info/ssoar/bitstream/handle/document/11362/ssoar-2006-ernst-freelancer.pdf?sequence=1http://www.deutsche-digitale-bibliothek.de/item/3TCBXRXTDLF7QZ3SYT5I5MWMR6N3TBBC