Online marketing doesn’t exist.
Marketing is about creating and executing strategies. One of the key marketing strategies is the communication one, which consists of two parts: the Copy strategy and the Media strategy. The former defines the pivotal elements of brand communication: Benefit, Support, and Tone. The latter refers, among other things, to the channels and media used to bring the copy to the target group.
Online is just one of the channels useful to communicate about your brand. It is NOT a particular kind of marketing and it does NOT require any specific strategy. At most, the online channel may require some sort of unique execution activities, but only if it stays coherent with the copy and media strategies.
Read the whole article about where digital fits in marketing.