Social Science should be obvious, though I’ve noticed the vast majority of CSS taps the sociology, psychology, economics and political science fields of social science rather than history, archaeology, law, etc. That will probably change over time.
Data Science is less obvious since it is a new field and in such demand that many people use the term to describe much less complex, older forms of computation. One of the largest data science recruiting firms is trying to resist the term being watered down by requiring the manipulation of text, audio, video or some other non-simple data format to be called data science. Others disagree, but the vast majority of commercial data scientists would agree that if you are never using machine learning (and not just linear regression which has been around a century), then you are not a data scientists.
Consequently, in the list of academic programs on the home page, I put an asterisk on the first PhD program that called itself Computational Social Science because George Mason’s program only includes machine learning if you take optional elective in machine learning. It is not required. Kings College London’s Master of Arts Big Data in Culture and Society program isn’t even listed, because it doesn’t appear to be much of a programming degree at all.
From looking at Carnegie Mellon’s PhD program and their faculty the program doesn’t seem to fit into the usual categories of social science used in CSS. But since it does look at policy, their graduates do often pursue work in government, and the computational side at CMU has few rivals in the world, I put aside my doubts to include it in the list.
The Computational Social Scientist 