We should not allow file extensions like xml, rtf, etc for Presentation Slides files. The only allowable file types are ppt, pptx, pps, ppsx and pdf. 

Instructors in the department can create/edit/delete their own courses. 
For example, Assistant Prof. Anderson can create a course post for "Data Structure". 
Prof. Lutts can have a course post like "Programming in Python".
Assistant Prof. Anderson can edit or delete "Data Structure", but not "Programming in Python"
Then, a role of basic member who has permission of creating, editing and 
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