Secondly: graphs storage is something which is very tempting in theory but very hard to get right in practice. I'm not going to say it is never appropriate (that is clearly untrue), but for most production applications it isn't the right choice.
I'd note for example that most social applications use a RDMS to store a single layer of friends (and then perhaps have a second graph DB for batch/stream processing of graph functions).
Firstly: RDF is an inadequate expression of most graphs, and SPARQL is a bad way to query graphs. See my comment here on this: https://news.ycombinator.com/item?id=14603090
Secondly: graphs storage is something which is very tempting in theory but very hard to get right in practice. I'm not going to say it is never appropriate (that is clearly untrue), but for most production applications it isn't the right choice.
I'd note for example that most social applications use a RDMS to store a single layer of friends (and then perhaps have a second graph DB for batch/stream processing of graph functions).