#1 Many-to-Many collection

[Kent Vogel]

I often have a Map of Sets, used to represent a
Many-to-Many relationship from one side, like:

a->1,2
b->2,3
c->5

Often, I need to 'reverse' this, so I can make lookups
the other way, giving me another Map of Sets which
looks like:

1->a
2->a,b
3->b
5->c

A few lines of code could do the transform, but it
would be nice to put both Maps of Sets into 1
'Relationship' collection, with a simple add method like:

void add(Object a, Object b)

and methods for looking up like:

boolean exists(Object a, Object b)
Object getLeft(Object a)
Object getRight(Object b)

[Not sure what good names for 'left' and 'right' or 'a'
and 'b' could be, maybe this could be generalized more]

It could well be represented internally as 2 Maps of
Sets, although there may be more efficient possibilities.

[Kent Vogel]

M2M Collection feature request in a pattern language

[Kent Vogel]

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Feature request re-stated in patern-like lingo. (See
attached file)

[Kent Vogel]

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Checked in initial revision of Relationship.java. It implements
a normal dependency relationship (1 way). Haven't decided
the best way to implement a 'reflexive' relationship.