Which one is the correct concept of Continental Crust and Oceanic Crust? I knew so far that, the classification of crust as SiAl-SiMa, vs. classification of crust as Continental-Oceanic; are completely different, as told in my school geography and university paleobiology class. (However I'm not a geology student)

Like, 



Where Continental crust and oceanic crust placed side-by-side, so, no-part of continental crust can cover-up oceanic crust. Also, in the places of continental crust; both SiAl and SiMa could be found

Now a geology student is telling me, that is wrong. SiAl is Same as Continental crust, and SiMa is same as Oceanic crust. He's Also telling, "SiAl or Continental crust lie upon Sima or Oceanic crust". That implies at the same-place on Earth, continental and oceanic crust occur together, one upon other.
Michael is correct. SIAL and SIMA are very vague and over-simplified summaries of the continental and oceanic crustal compositions. These terms may be OK for school introductions to geology, but you don't have to look far to find many exceptions. There are eroded and fragmented continental remnants, of nominally SIALic composition, in every ocean. Indeed, 100% oceanic crust may include small amounts of highly differentiated plagiogranite (technically SIALic in composition). Then there are bits of oceanic crust, called ophiolites (SIMA) incorporated into continental crust through processes of obduction and terrain accretion, not to mention the many flood basalt terrains (SIMA), which can occur on either continental or oceanic crust. Whether crust is oceanic or continental is a matter of overall rock density, composition and crustal thickness.