I have (obviously) heard a lot of Hebrew names of the form "Ploiny ben Almoiny," where Almoiny is Ploiny's father. But occasionally I see names written with the Aramaic "bar", for example Simon bar Kokhba, R'Mari bar Rochel, Simeon bar Yochai, and R'Yosef bar Dovid. "Bar" could be meaning בר or ב"ר; I'm not sure which. Some of these guys are old enough that an Aramaic-style name does not seem at all strange, but I have seen the "bar" in contemporary contexts, too. What is the difference, if any, between "ben" and "bar"? What determines which form--"ben" or "bar"--is used?