Link Building Structures: Hunters and Collectors

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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.

Blog network types - graph theoryIn 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:

  1. Hub – This type has a central hub site, which could cover a general range of topics and send traffic to niche sites.
  2. Collectors – This type has a central site but it might collect traffic from, say, keyword domains (collectors).
  3. 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.

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  • What you call a “clique network” (a term used in academic literature) has been known as a “link farm” since around 2000 in the SEO industry.

    However, link farms are only one type of clique network, but many people will quickly recognize the model. The stigma associated with link farming makes clique networks in general less attractive to the SEO community.

    A bi-directional hub offers SEO value in that it helps ensure an equal, improved chance of crawling for all node sites. A unidirectional hub offers less opportunity for crawling unless it is well-linked from other points on the Web.

    Given a choice between a unidirectional hub with no inbound links and a bi-directional hub with 1 or more node points, the bi-directional hub offers greater SEO value.

    Given a choice between two hubs regardless of whether either is bi-directional or unidirectional, the hub with more value-passing inbound linkage offers the greater SEO value.

  • @Michael: Okay, I wasn’t aware that link farms had fully-connected graphs. I was under the impression that that wasn’t necessarily the case. My terminology is by no means official, but tends towards graph theory in general. I didn’t use pure SEO terms because I’m discussing generalities.

    By “clique” I mean a “network” of fully connected sites. I.e., each hyperlinked to another. That may or may not mean a link farm, especially since a blog network falls under the legitmate use of this graph structure.

    But a topical clique, where every site covers the same topic and is connected to every other site in the group, leans more towards being a link farm. Hence why I didn’t use that terminology

  • SEOs are probably like doctors or scientists in that they disagree with each other at times. I’ve believe I’ve read – though my memory fails – that bi-directional hubs are not of much value, and that’s better to send traffic in a particular direction.

    I supposed it depends on how you plan to use the “hunter and collector” sites and their traffic.

  • What’s wrong with 5 or 6 sites that know each other’s comments that link to each other almost exclusively?

  • @Ken: Because if these sites never link out, then it’s a clique. Google, I believe, wants to promote more connected graphs (the0retical). It helps them to index sites. Linking out is a sort of human filtering for them, and supposedly gives a vote of relevance to a linked to site, other factors considered. Lack of new outbound links doesn’t add to the process. And who knows what algorithm changes are queued for the future 🙂

  • I like things that get me thinking and this page has. Love the graphics and glad I have found your site.

    As to your last comment, I think you have hit the nail on the head.