How do associations, @NS and @NV work in UniData Dictionaries?

Question

Does anyone have a quick example of how Associations, @NS and @NV work in UniData?

I’m trying to work out associations in dictionary items but cannot get them to do anything.

For example, in a record

<1,1> = A
<1,2> = B
<2,1> = Apple
<2,2> = Banana

I created 3 dictionary items. LETTER and FRUIT, COMBO as follows

LETTER:

<1> = D
<2> = 1
<3> = 
<3> = Letter
<4> = 6L
<5> = M
<6> = COMBO

FRUIT:

<1> = D
<2> = 1
<3> = 
<3> = Letter
<4> = 6L
<5> = M
<6> = COMBO

COMBO:

<1> = PH
<2> = LETTER FRUIT

Doing a LIST LETTER FRUIT or LIST COMBO has no difference to when LETTER and FRUIT do not have an association declared in 6.

At this point I thought it might group multivalues together when SELECTing so I created another record as such:

<1,1> = A
<1,2> = B
<2,1> = Banana
<2,2> = Apple

Doing SELECT MyFile WITH LETTER = “A” and FRUIT = “Apple” selects both records, so that cannot be it either.

I then tried changing LETTER to be:

<1> = I
<2> = EXTRACT(@RECORD,1,@NV,1);EXTRACT(FRUIT,1,@NV,1);@1:" (":@2:")" : @NS
<3> = 
<3> = Letter
<4> = 6L
<5> = M
<6> = COMBO

Hoping it that a LIST MyFile LETTER would bring back all the different letters with their associated fruit in parentheses. That didn’t work either as now LETTER only ever displayed the first Multivalue instead of all of them. For Eg:

LIST MyFile LETTER 14:05:22 26 FEB 2010 1
MyFile.... LETTER..............

RECORD2    A (Banana)1
RECORD     A (Apple)1
2 records listed

The manuals don’t go any further than saying the word “association”. Is anyone able to clarify this for me?

Answer 1

To answer part of my own question:

Only 'WHEN' is affected by the association, not with. If you turn on UDT.OPTIONS 94 and do

LIST MyFile WHEN LETTER = "A" AND FRUIT="Apple" COMBO

when using my D-Type definition of LETTER, I get

LIST MyFile WHEN  LETTER = "A" AND FRUIT="Apple" LETTER FRUIT 16:06:42 26 FEB 2010 1
MyFile.... LETTER.............. FRUIT...............

RECORD     A                    Apple
1 record listed

Which is what one would expect.

To use the WHEN clause you need to be in ECLTYPE U, not P. IT would be helpful if this was clearer, but oh well...

Answer 2

Many times NV and NS only work when using BY-EXP in your LIST or SELECT statements. You need to use modifiers that specifically look at MultiValue and SubValues.

WHEN is one, and BY-EXP is another. There are other, but not sure what they are off the top of my head. I primarly use BY-EXP and BY-EXP-DSND.

LIST MyFile BY-EXP LETTER = "A" BY-EXP FRUIT ="Apple" LETTER FRUIT LETTER.COMBO

To bring back all the combinations, you use need to do the following:

LIST MyFile BY-EXP LETTER LETTER FRUIT LETTER.COMBO

Change the following virtual field from 'LETTER' to say 'LETTER.COMBO' or something along those lines:

<1> = I    
<2> = EXTRACT(@RECORD,1,@NV,1);EXTRACT(FRUIT,1,@NV,1);@1:" (":@2:")" : @NS    
<3> =     
<3> = Letter    
<4> = 6L    
<5> = M    
<6> = COMBO  

Hope that helps.

-Nathan