This is a brief introduction to graph theory as it applies to both internal and external link building. The concepts here will be re-used in future posts, and I’ll refer back regularly.
It’s my guess that Google has hired numerous employees with PhDs in Mathematics for a variety of reasons, one being that their PR (PageRank) algorithm requires a graph theoretic approach to analyzing links, to determine whether or not they are “natural” and “organically grown”. Before getting too deep into analysis, which I’m leaving for later posts, let’s have a look at a few types of simple link structures for any collection of sites. For convenience, I’m referring to each collection here as a “network”, thought that does not mean the same person owns all the sites.
In graph theory, the term “connectivity” has to do with inbound (in-degree) and outbound (out-degree) behavior of each node in the graph. So if a node has 3 links coming in and 2 going out, then it has an indegree of 3 and an outdegree of 2, which can be written out(3)/ in(2). PageRank, of course, is only partially determined by in/out degree of a website and its pages.
Each node in out network graphs can represent either a single web page or an entire website, though in this case, let’s focus on the latter. (In any particular graph, it’ll be exclusively one or the other.)
Here are the connectivity graphs of a few simple types of blog networks:
- Hub – This type has a central hub site, which could cover a general range of topics and send traffic to niche sites.
- Collectors – This type has a central site but it might collect traffic from, say, keyword domains (collectors).
- Fully connected – This is the clique network I discussed previously, which is either a topical clique or likely a blog network. Every site in the network is linked to every other site. That is, the graph representation is “fully connected.”
One other common/ simple graph type that is not shown here is the bi-directional hub. This one is a combination of the first two types. That is, the hub site is hyperlinked bi-directionally to each satellite site. I have yet to determine any SEO value in such a site. In my opinion, this structure dilutes traffic. The other structures, however, have a great deal of value, and I’ll discuss them and hybrid graphs shortly. Herein lies methods for alternative linkbuilding.