# Social network representation: graphs or sets?

for social network representation, what is better, sets or graphs ? What kind of feature the first gives that the second doesn't and viceversa?

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A graph is a set that has additional structure -- specifically, it has structure representing the connections between its elements (and possible other information, such as the strength of the connection if it's a weighted graph). If you need to represent connections between elements you should use a graph representation of the problem. If you're doing computations, the fact of how to implement your graph on the computer is another question - there are at least three possible representations which offer different benefits and drawbacks. –  Chris Taylor Aug 30 '11 at 9:25
Not every question about graphs is graph theory, and not every question about sets is set theory. In this case, this question is neither. –  Asaf Karagila Aug 30 '11 at 9:32
Hmm... from the title, I kind of expected the question to be about deep foundational issues and to involve things like Aczel's axiom. I guess I was wrong. –  Ilmari Karonen Aug 30 '11 at 10:48
The more I think about it, the more I'm starting to doubt that the question is mathematical in its nature. –  Asaf Karagila Aug 30 '11 at 11:10
@Niel: If this were on SO, I'd be inclined to tag it as data-structures (and probably also social-networking‌​). Perhaps we could use such a tag here, or perhaps the problem is that the question really belongs elsewhere. –  Ilmari Karonen Aug 30 '11 at 11:10

For instance, as a potential foundation for mathematics, sets can be used to do essentially anything if you put your mind to it. For instance, sets can be used to represent a graph. You can represent a graph as a set of labelled nodes, and the edges $u\text{-}v$ are represented by unordered pairs $\{u,v\}$ (which will be singleton sets in the case of self-loops). Or you can represent a graph as a set of labelled edges, where the nodes are given as collections of edges $\{e_1, e_2, \ldots, e_k\}$ which meet one another (and where each edge can belong to at most two such sets).