Chris Withers wrote: > > Steve Alexander said he was going to have a think, but I haven't heard > anything since he mentioned it... I'll have to start running a Kibo-bot soon :-) I've got as far as defining the difference between the two acquisition behaviours. Warning: The following goes into some detail about acquisition algebras. There are lots of nested parentheses with letters in them. Let's say we have the following object tree. The upper-case letters represent names, not identity. The lower-case letters represent identity. / |-A a | |-B b | |-X x | |-P p1 | |-Y y | |-P p0 Let's consider the path X.Y.A.B.P in both types of acquisition. Containment first: Start at the root. Look for X. Find X at x. Look for Y in x. Find Y at y. Look for A in y. Not found, so look for A in x. Not found, so look for A in /. Found as a. Look for B in a. Found as b. Look for P in b. Not found, so look for P in a. Not found, so look for P in /. Found as p0. Context first Start at the root. Look for X. Find X at x. Look for Y in x. Find Y at y. Look for A in y. Not found, so look for A in x. Not found, so look for A in /. Found as a. Look for B in a. Found as b. Look for P in b. Not found, so look for P in a. Not found, so look for P in y. Not found, so look for P in x. Found as p1. The acquisition algebra is based on the "of" operator: (object of context). The difference in algebra is that with containment-first, as you build up the expression, you add to it using the last object you searched as the context part of the expression. With conext-first, you need to add the whole expression so far as the context part of the expression. Containment first: Start at the root. (X of /) Look for X. Find X at x. (Y of X) of (X of /) Look for Y in x. Find Y at y. (A of /) of ((Y of X) of (X of /)) Look for A in y. Not found, so look for A in x. Not found, so look for A in /. Found as a. (B of A) of ((A of /) of ((Y of X) of (X of /))) Look for B in a. Found as b. (P of /) of ((B of A) of ((A of /) of ((Y of X) of (X of /)))) Look for P in b. Not found, so look for P in a. Not found, so look for P in /. Found as p0. Context first Start at the root. (X of /) Look for X. Find X at x. (Y of (X of /)) of (X of /) Look for Y in x. Find Y at y. (A of (Y of (X of /))) of ((Y of (X of /)) of (X of /)) Look for A in y. Not found, so look for A in x. Not found, so look for A in /. Found as a. (B of (A of (Y of (X of /))) of ((Y of (X of /)) of (X of /))) of ((A of (Y of (X of /))) of ((Y of (X of /)) of (X of /))) Look for B in a. Found as b. (P of (B of (A of (Y of (X of /))) of ((Y of (X of /)) of (X of /))) of ((A of (Y of (X of /))) of ((Y of (X of /)) of (X of /)))) of (B of (A of (Y of (X of /))) of ((Y of (X of /)) of (X of /))) of ((A of (Y of (X of /))) of ((Y of (X of /)) of (X of /))) Look for P in b. Not found, so look for P in a. Not found, so look for P in y. Not found, so look for P in x. Found as p1. I just put that in to give Chris a fright :-) You can see from this that the algorithm is more complex. Acrually, it can be rather simplified, because what I've written out in full above contains many internal repetitions. In C terms, these become pointers to the same acquisition wrapper. So the following... (P of (B of (A of (Y of (X of /))) of ((Y of (X of /)) of (X of /))) of ((A of (Y of (X of /))) of ((Y of (X of /)) of (X of /)))) of (B of (A of (Y of (X of /))) of ((Y of (X of /)) of (X of /))) of ((A of (Y of (X of /))) of ((Y of (X of /)) of (X of /))) ...is really this: ((P of q) of q) where q is ((B of r) of r) where r is ((A of s) of s) where s is ((Y of t) of t) where t is (X of /) I also wonder whether we need the second part of all the context-first expansions above. That is, whether (P of q) will do, instead of ((P of q) of q). To see if the simplification works, let's take the example of acquiring X.Y in the tree: / |-X |-Y Containment first: (X of /) (Y of X) of (X of /) Simplified Context first: (X of /) (Y of (X of /)) Applying this simplification to my larger example above, we get for the following: Simplified Context first Start at the root. (X of /) Look for X. Find X at x. (Y of (X of /)) Look for Y in x. Find Y at y. (A of (Y of (X of /))) Look for A in y. Not found, so look for A in x. Not found, so look for A in /. Found as a. (B of (A of (Y of (X of /))) Look for B in a. Found as b. (P of (B of (A of (Y of (X of /))) Look for P in b. Not found, so look for P in a. Not found, so look for P in y. Not found, so look for P in x. Found as p1. The search just proceeds as you read from left to right. There are no repeated searches, unless you specify a repeated search (such as A.B.A.A.B.C). Therefore, there is little need to simplify expressions in the simplified context-first algebra. -- Steve Alexander Software Engineer Cat-Box limited http://www.cat-box.net _______________________________________________ Zope-Dev maillist - [EMAIL PROTECTED] http://lists.zope.org/mailman/listinfo/zope-dev ** No cross posts or HTML encoding! ** (Related lists - http://lists.zope.org/mailman/listinfo/zope-announce http://lists.zope.org/mailman/listinfo/zope )

- [Zope-dev] Acquisition Confusion :S Chris Withers
- Re: [Zope-dev] Acquisition Confusion :S Evan Simpson
- Re: [Zope-dev] Acquisition Confusion :S Chris Withers
- Re: [Zope-dev] Acquisition Confusion :S Evan Simpson
- Re: [Zope-dev] Acquisition Confusion :S Chris Withers
- Re: [Zope-dev] Acquisition Confusio... Evan Simpson
- Re: [Zope-dev] Acquisition Conf... Chris Withers
- Re: [Zope-dev] Acquisition ... Steve Alexander
- Re: [Zope-dev] Acquisition ... Chris Withers
- Re: [Zope-dev] Acquisition ... Steve Alexander
- Re: [Zope-dev] Acquisition ... Chris Withers
- Re: [Zope-dev] Acquisition ... Steve Alexander
- Re: [Zope-dev] Acquisition ... Michel Pelletier
- Re: [Zope-dev] Acquisition ... Chris Withers
- Re: [Zope-dev] Acquisition ... Evan Simpson
- Re: [Zope-dev] Acquisition ... Chris Withers
- Re: [Zope-dev] Acquisition ... Evan Simpson
- [Zope-dev] Acquisition ( sl... Chris Withers