XnView Software

It would be very helpful to have this, as a category typically is not only a specification of only one category but of more than one.
Making it possible would reflect "real word relations" much better.

In actual version of MP if I generate a category with the same name as a category somewhere else, they are handled differently.
Which is confusing anyhow.

some people ask for the opposite,
stamps
--------japan
-------spain
travel
------france
------japan
but I agree with you. (but I didn't completely understand your wish)
I think a keyword should be unique

Well, actually the labels ARE unique, if I get it right.

Taking your example from above:
"japan (stamps)" and "japan (travel)" are different.
"japan" sole does not exist.

You can only filter on "japan (stamps)" or "japan (travel)",
but you cannot filter on all items with "japan" (wether travel, stamps or whatever).

What I mean by inheritence is:
To understand a subcategory as specification
(the parent category is the generalization then).
Animal
--- dog
--- cat

There are "dogs", "cats" and "animals".
Sub categorizing has the meaning:
every dog is an animal, every cat is an animal.

Taking your example again:
I would like to label all items concerning Japan
(in any way: travel, stamps, eating, ...) with "japan".
And "japan" is semantically of no inheritence relation to "travel", "stamps" etc.
If you want items with "travel" and "japan" ...
well choose both in filtering.

Multiple inheritence (that's what my proposal is about) means
that a category may be sub category of many parent categories
(while the latter or of no relation to the sub category).

... short addendum:

As wording is important ...

"parent categories":

Actually MP realizes just the simple and weak concept of partitioning.
I suggest the stronger concept of specification, generalization, inheritence.

... no, still not correct somehow ...

I've the feeling I'm not good in explaining what I mean.

A sub category should not be specific to its parent category
(as it is realized in MP now).
It is a specification for its parent category, but it should be possible
to be specification of other categories too.

(Yes, that sounds better )

... and an example does better than thousand words

Take "Paris" as sub category of both "France" and "Capital".