[Data-modeling] graph, nodes, relationships - a few questions

[Roland Bouman]

Hi All!

this is the first time I'm posting on the data-modeling list - i hope
this is the right place.

I am trying to understand MQL so I'm reading the MQL Reference Guide.
I have a few questions about a few things I read, and I was hoping to
get some help here.
In particular, I am a tad confused about some of the things I read in
http://mql.freebaseapps.com/ch02.html

In "2.1. Nodes and Relationships"
(http://mql.freebaseapps.com/ch02.html#id2942817) it reads:

"...the Metaweb graph is a set of nodes and a set of links or
relationships between those nodes.
....however, the nodes in the graph hold no information themselves.
....All the interesting data in the database is stored in the form of
relationships between nodes (or between nodes and primitive values).
...Graphs can be represented visually using circles to represent nodes
and arrows between the circles to represent relationships.
"

So far, so good. As I continue reading "2.2. Properties"
(http://mql.freebaseapps.com/ch02.html#id2943383), I am confused by
this:

"...You may have wondered about the fact that these property
identifiers look so much like node identifiers.
....this means, of course, [..] that properties are themselves nodes
in the Metaweb graph.
....Since properties are nodes, they can appear in the From column of
a table of tuples, and can have relationships themselves."

Now, from what I understand, these "properties" are actually
relationships (it's just represented as property in the tabular
representation of the graph).
But to me this sounds like it contradicts 2.1:

One the one hand, nodes hold no information themselves, rather the
relationships between nodes hold the interesting information, yet at
the same time, relationships are themselves actually nodes.
I also have trouble how this would be visualized "using circles to
represent nodes and arrows between the circles to represent
relationships".
I mean, I can see how it is possible to still visualize a graph if you
elect beforehand which nodes to draw as circles, and which ones as
connecting lines,
but my gut feeling says you cannot visually represent the same node
both as a cirle and as a connecting line without duplication.

Just to be clear - I am not interested in actually drawing graphs  - I
am just looking for a way to understand this node/relationship
duality.

I'd greatly appreciate any pointers / explanations.

kind regards,

-- 
Roland Bouman
http://rpbouman.blogspot.com/

Author of "Pentaho Solutions: Business Intelligence and Data
Warehousing with Pentaho and MySQL",
http://www.wiley.com/WileyCDA/WileyTitle/productCd-0470484322.html