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Yet another tweak to the formal definition. Much better this time.

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http://www.cse.unsw.edu.au/~willu/ 2009-10-08 22:59:34 -04:00 committed by Joey Hess
parent 4299f22ae8
commit 6533bec35a
1 changed files with 9 additions and 7 deletions
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doc/todo/dependency_types.mdwn
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@ -339,17 +339,17 @@ can indirectly influence what pages a pagespec matches.
> Trying to make a formal definition of this: (Note, I'm using the term sets rather than lists, but they're roughly equivalent)
>
> * Let the *matching set* for a pagespec be the set of existing pages that the pagespec matches.
> * Let the *assignment dependent glob matching set* for a particular assignment of True/False to the `match_()` functions of a pagespec, be the set of pages that would match if the `match_()` functions returned those true/false values.
> * Let the *glob matching set* be the intersection of all assignment dependent glob matching sets. i.e. the set of pages that can match this pagespec just based on glob information, regardless of what the `match_()` functions return.
> * Let the *missing document matching set* be the set of pages that would match the spec if they didn't exist. These pages may or may not currently exist. Note that membership of this set depends upon how the `match_()` functions react to non-existant pages.
> * Let the *indirect influence set* for a pagespec be the set of all pages, *p*, whose alteration might:
> * cause the pagespec to include or exclude a page other than *p*, or
> * cause the pagespec to exclude *p* unless *p* is in the glob matching set.
> * cause the pagespec to exclude *p*, unless the alteration is the removal of *p* and *p* is in the missing document matching set.
>
> Justification: The 'base dependency mechanism' is to compare changed pages against each pagespec. If the page matches, then rebuild the spec. For this comparison, creation and removal
> of pages are both considered changes. This base mechanism will catch:
>
> * The addition of any page to the matching set through its own modification/creation
> * The removal of any page *that would still match if it existed* from the matching set through its own removal. (Note: The base mechanism cannot remove a page cannot from the matching set because of that page's own modification. If the page should be removed, then cannot match the spec after the change.) This 'match after the change' criterion is what I tried to capture in the glob matching set above. I think my glob matching set is slightly more restrictive than the set of pages that 'still match after the change', but more restrictive is safer than less restrictive for that set.
> * The removal of any page *that would still match while non-existant* from the matching set through its own removal. (Note: The base mechanism cannot remove a page cannot from the matching set because of that page's own modification (not deletion). If the page should be removed matching set, then it obviously cannot match the spec after the change.)
> * The modification (not deletion) of any page that still matches after the modification.
>
> The base mechanism may therefore not catch:
>
@ -357,7 +357,6 @@ can indirectly influence what pages a pagespec matches.
> * The removal of any page from the matching set through its own modification/removal if it does not still match after the change.
>
> The indirect influence set then should handle anything that the base mechanism will not catch.
>> At the moment the indirect influence set is a little conservative, in that the glob matching set doesn't exactly equal the set of pages that still match after the change. It is quite hard to get this right - thoughts on tuning the glob matching set definition are welcome. I've tried to err on the side of a longer indirect influence set, as that will make sure we do enough updates.
>
> --[[Will]]
@ -398,8 +397,8 @@ can indirectly influence what pages a pagespec matches.
The removal or (re)creation of foo changes what pages match it. Note that
this is true even if the pagespec currently fails to match.
>>> This is an annoying example. I think the indirect influence list must contain 'foo' and all currently matching pages. `created_before(foo)` will not match
>>> a deleted page, and so the base mechanism would not cause a rebuild. The removal problem strikes. Note that the glob matching set is empty in this case. -- [[Will]]
>>> This is an annoying example (hence well worth having :) ). I think the indirect influence list must contain 'foo' and all currently matching pages. `created_before(foo)` will not match
>>> a deleted page, and so the base mechanism would not cause a rebuild. The removal problem strikes. -- [[Will]]
* The pagespec "foo" has an empty influence list. This is because a
modification/creation/removal of foo directly changes what the pagespec
@ -436,6 +435,9 @@ can indirectly influence what pages a pagespec matches.
that contains index (because a change to index changes the backlinks).
Note that this is true even if the backlink currently fails.
>>> This is another interesting example. The missing document matching set contains all links on the page index, and so
>>> the influence list only needs to contain 'index' itself. -- [[Will]]
* The pagespec "link(done)" has an influence list that
contains every page that it matches. A change to any matching page can
remove a link and make it not match any more, and so the list is needed