They can be, but democratic socialist is a much more vague term than social democrat. A social democrat is basically a liberal who supports the welfare state and wants to reform capitalism, maaaaaybe try to get rid of private control of the means of production through reformism but most likely not. A "democratic socialist" can be anything from anarchism to market socialism to parecon depending on who's using the term. It really just means "not Marxist-Leninist/Maoist/Stalinist/Hoxhaist/state socialist!"