Relation Graph Cardinality Question

[LelandLong]

FMP tries to indicate the cardinality of a relationship using a straight line or "crows foot" up to the TO. But there is another that shows up occasionally that I cannot find any references to! I wondered if there was anyone out there that could point me to one or more places to find out what it is meant to represent.

I'll attach a jpeg to illustrate.

[David Jondreau]

Storage.

Specifically, global fields and unstored calcs show with the pipe.

[comment]

IMHO, it means that the relationship only works in one direction.

Maybe a better way to put it: there are no "related records" at the end marked with the "T".

Edited January 28, 2008 by Guest

[David Jondreau]

Not sure about this since I didn't test all possibilities, but...

Straight line: When the field is defined as Auto-Enter or Validate Unique.

T or Pipe: When field is defined as global or unstored.

Crow's feet: Everything else

No connection between the lines and how many related records there actually are.

[comment]

No, I meant the graph says "there will be no 'related records' on this side, no matter what you do". In graphical terms: if you follow this line, you will get to a roadblock.

[Breezer]

I agree with Comment. Another way to look at it is, on that side, the record is a UNIQUE key hence "no other record in that side of the table will have a duplicate of the key field." for instance, if you looked at that column, there will be one and only one occurence of each value. this can either be the primary key field or another field that can be used as a primary key field. A primary key field is a field that can be used to uniquely identify a row and in filemaker terms, a record.

http://en.wikipedia.org/wiki/Candidate_key

http://en.wikipedia.org/wiki/Primary_key

ROW = RECORD

COLUMN = FIELD

Edited January 28, 2008 by Guest

[David Jondreau]

I agree with comment too. And with Leland when he says Filemaker "tries to indicate" the cardinality. In the case of the T, it's likely 100% accurate. In the cases of the crow's feet and the direct line, it's more a strong suggestion of what should be happening.

Frex, a person unwise in the way of keys can force a field FM thinks is a primary key to have duplicates.

[comment]

I believe it indicates how it's going to index the related records (or, in case of "T" - how it's NOT going to index them).

[David Jondreau]

Nope, the Crow's feet/ straight line is directly related to Unique validation and Auto Enter serial.

[comment]

I believe indexing is also related to those. I remember -Queue- once demonstrated how relationships with a straight line were faster than crow's feet - unfortunately, that thread was on a forum that doesn't exist any more.

[normanicus]

It appears to mean that the field at that end of the line cannot be indexed.

[comment]

Really? :jaw:

[David Jondreau]

LOL!

[normanicus]

the record is a UNIQUE key hence "no other record in that side of the table will have a duplicate of the key field

This doesn't actually appear to be correct. If you make a relationship with a calculation field (I call it 'Match All') on each side and set these fields to both contain 1 then the relationship will show with the straight line.

Changing that calculation to 'Unstored' on one of the fields changes the relationship graph symbol to -|. So this does not accord with your statement.