yeah im no mathematician but i dont think you can use just part of
a theory thats designed for flow diagrams with some totally
different kind of diagram.
well, relational algebra, or graph theory is just that, and can be
used for wbatever one finds applicable. diff Application aspects may
noting that, i have
spent almost no time at all on supporting concrete patterns at
this point (also, nobody has really complained).
no worries, i've doing now a cut over proper graph, built in
similar way as the one unitofwork's topology is using,
scratch that, instead i propagated a
i am asking this, because so far i am considering both
table/foregn-key graph and mapper/relation graph same, thus applying
the mincut for the table/foregnkey (which sets fkey.use_alter=True)
also to the other (which sets respective relation.post_update=True).
And in 99% of cases, this works.
a circular relationship between two mappers means that a dependency
sort revealed that the mapper-level dependency graph contains cycles.
that portion of the sort is then thrown away and replaced with a
dependency sort where the nodes are individual object instances.
so sort #1 is mappers as
A mincut algorithm finds the minimal number of edges to cut in a
cycled graph so it becomes without cycles.
http://en.wikipedia.org/wiki/Max-flow_min-cut_theorem
i.e. applying such algorithm over the graph of table dependencies
(foregnkey), one gets some minimal number of foreign keys to make
On Feb 2, 2007, at 10:33 AM, svilen wrote:
A mincut algorithm finds the minimal number of edges to cut in a
cycled graph so it becomes without cycles.
http://en.wikipedia.org/wiki/Max-flow_min-cut_theorem
i.e. applying such algorithm over the graph of table dependencies
(foregnkey), one
i think you are looking for a feedback arc set, which describes
exactly the problem that applying post_update to a mapping
solves:
http://en.wikipedia.org/wiki/Feedback_arc_set
and we actually generate a set like this in the _find_cycles()
method, except it doesnt find just one edge of
On Feb 2, 2007, at 2:14 PM, svilen wrote:
of course, topological sort is a sort, but in order of it to work, the
graph should not have cycles. Which are cut by use_alter's and
post_updates, on foreign keys and relations.
well, in our case all edges have cost of 1, except
