[Zope3-dev] Second ZOPE 3 mini- NEWSLETTER (and kinda large glossary)

[Steve Alexander]

Tres Seaver wrote:

> On Thu, 2002-10-31 at 11:44, Gary Poster wrote:
> 
>> Point taken: I lost accuracy in my pursuit of friendliness.  Would
>> you buy "reside in the traversable Zope tree"?
> 
> 
> Maybe even "are reached by traversing the Zope object tree", or
> "having traversal context"?


I like to think of traversal as being like taking a walk somewhere.

To talk about traversal in Zope 3, by analogy...

I always start my walk in the same place, at home. (The root folder.)

The route my walk will take is given to me as a series of instructions:

   /front_porch/end_of_road/bus_stop_by_newsagent/catch_bus/to_town

I take each instruction in turn, and interpret what it says in the 
context of where I am at the time I read that instruction.

This series of instructions is like a traversal path. The following 
series of actions is like the traversal process.

So, I start at home, and I read "front_porch". Ok, so I go out of my 
front door and into the porch.

Now, I'm standing outside my front door, and I read "end_of_road". So, I 
walk to the end of the road and read the next instruction.

The next instruction says "bus_stop_by_newsagent".So, I look around, see 
the newsagent and walk up to it. Ah, there's a bus-stop here. Great.

The next instruction is "catch_bus". Previously, the instructions had 
been places to go that I can see from where I am. However, in the 
context of a bus-stop, taxi rank or train station, I know that I can 
interpret the instruction as either a place to go, or a thing to do. 
There's nowhere around that could be called "catch_bus", so I'll 
interpret it as a thing to do. I wait for a bus to arrive, and get on it.

The next instruction is "to_town". In the context of being on a bus, the 
instruction is always interpreted as the destination to buy a ticket 
for. So, I buy a ticket to town.

I get off the bus in town. My journey is complete.


Let's say that just after I arrive in town, I have this overwhelming 
urge to read a newspaper. Well, I remember that I caught the bus from 
outside a newsagent, so I can just retrace my steps to that newsagent, 
buy a paper, and return to town again.

The newsagent is a bit like a placeful service -- I can use its 
facilities because I know how to get to it. I know how to get to it 
because I passed it on my way to my destination.

If I wanted to see a film instead, well, I couldn't do that as I didn't 
pass a cinema on the way. (For users of American English, s/film/movie/ 
and s/cinema/theater/.)

A global service would be something like the air, which I might like to 
breathe from time to time, or like gravity, which I might like to use to 
help me sit down on a seat in the bus.

--
Steve Alexander