Use of '@' '.' and 'public operator/keywords in Oracle database? I got into a weird SQL query-patch which looks for @ . and public keywords.  I was wondering what is the purpose of these operators/keywords? 

I suspect that it might be looking for SQL injection or some weird buffer overflow 
but I can't seem to understand why it looks for those characters, etc, and I can't find much information about those keywords.

If anyone could enlighten my eyes, it will be very helpful.
This diagram is from the Oracle Docs Syntax for Schema Objects and Parts in SQL Statements page:  



It shows the general use of the period character (.) for qualification and the @ symbol for referencing dblinks.

The @ symbol is also used when creating dblinks.

Given that the public keyword is also used for creating them, I think it is likely that your external function is doing something with dblinks!