Date formats, slash (/) and dot (.)

Hello,
1) Are slash and dot date format delimiters locale /culture notations or any other notation standard like database, iso?
I read about ISO 8601 date standards, about SQL Server formats, they talk about yyyy-mm-dd. I also read about language-dependent worded date notations such as “24. Dezember 2001” (German) or “February 4, 1995” (US English). In .NET Short, Long, etc. representation of date formats are all with slashes. But most often date formats i meet are MM/dd/yyyy, dd/MM/yyyy and dd.MM.yyyy and i'm not sure where they come from!
2) How decide in what format to represent your dates to website users, i mean with slashes or dot?
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