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Subject: Re: [xdi] More example graph notation reflecting comments

• From: Drummond Reed <drummond.reed@xdi.org>
• To: Joseph Boyle <planetwork@josephboyle.net>
• Date: Wed, 11 Sep 2013 10:15:20 -0700

On Wed, Sep 11, 2013 at 10:09 AM, Joseph Boyle wrote:
What would you think of squares for the value context nodes? A rectangle is reminiscent of a UI text field that contains a value.

I personally like the symmetry of using only two shapes - circle and diamond. Secondly, I think the open shapes help reinforce that these are "end" nodes -- the open circle is a root (starting point in the graph) and the open diamond is a value (ending point in the graph). Thirdly, the diamond shape mimics the syntax for all attributes.

On Sep 11, 2013, at 9:50 AM, Drummond Reed <drummond.reed@xdi.org> wrote:

Per the previous thread, I've created two more versions of a simple example graph reflecting Markus's and Joseph's suggestions.

The first one eliminates the multiplicity characters in the shapes. I must agree with Markus, this makes the graph look much simpler visually. OTOH, I disagree with Markus that it's not worth using different shapes for entity nodes and attribute nodes. Especially in this simplified form (without the multiplicity characters inside the shapes), I think it is very valuable to be able to see in a glance which nodes are entities and which are attributes and which are values.

<image.png>
The second example below is even simpler. It reflect Joseph's suggestion of removing the literal arcs and just putting the value (if there is one) next to the value node. I must admit, I really like this just because of how simple and intuitive it is. If a value node has a value, it is shown, otherwise no value is shown and it is undefined.

<image.png>

I appreciate Markus's point about showing the three kinds of arcs in the XDI graph model, because I do think this is a very important part of the model. However in terms of teaching the XDI graph model, it seems to make it much simpler if we leave out the detail of needing a literal arc and & predicate every time you have a value. Rather, my suggestion is that  we explain that once (and show it once) up front when we are introducing the notation, and then leave it out after that.

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