BusinessObjects Board

fan trap question

building semantic layer
#1

in the designer manual (6.5), page 264 it identifies fan traps in the beach universe. Does anyone know why it highlights variety <product < salesline and it doesnt mention variety <product <loanline or variety< product< prdcolor as beig fan traps, yet they look to me to be. am i misunderstanding what is a fan trap?

thanks

johnwxyz (BOB member since 2008-01-26)

#2

Hi,
Pleas go through this link.
PDF .
Click on the first link. It’s PDF which will give you the exact idea of traps.

Omkar Paranjpe :us: (BOB member since 2006-02-13)

#3

Hi omkar

thanks for your response, i have read the documentation on fan traps, but still cannot see why they list only the one fan trap in the example

do you have any idea?

johnwxyz (BOB member since 2008-01-26)

#4

Your copy of the “beach” universe must be different from mine. :slight_smile:

To officially be a fan trap the series of tables should have measures on at least two levels. If you don’t have measures, then it doesn’t matter if the tables share a one-many relationship or not.

Dave Rathbun :us: (BOB member since 2002-06-06)

#5

ok not beach , but a car database bo are using as an example

dont have the car database that the manual is referring to, i’ll watchout for measure count on fantraps in future

thanks

johnwxyz (BOB member since 2008-01-26)

#6

Ah, the famous Motors 2000 database. Yes, that one I know.

I posted a summarized fan trap description here.

Dave Rathbun :us: (BOB member since 2002-06-06)

#7

This is page 228-229 on the Latest Designer’s Guide with is available at the http://support.businessobjects.com/documentation/product_guides/default.asp as of today 03-03-2008.

To answer your question:

variety< product< prdcolor is not a potential fan trap because prdcolor has no measure objects. Is all ID’s linking ColorID to ProductID.

variety <product <loanline may be a potential fan trap because of measures PRODUCT.PRODPRCE and LOANLINE.LLQUANT and any query with VARIETY NAME, PRODUCT NAME, PRODUCT PRICE & LOAN QUANTITY may result in overinflating aggregates on PRODUCT PRICE.

The manual does not considers it as fan trap. Probable because it may be on a different context or other reasons beyond my understanding !

deepak115 :us: (BOB member since 2007-12-01)

#8

Normally price is an attribute (dimension or detail) rather than a measure. Price by itself should not be aggregated.

Dave Rathbun :us: (BOB member since 2002-06-06)

#9

and I would assume that until the Designer’s Guide mentioned the same object/column (PRODUCT.PRODPRCE) for considering VARIETY < PRODUCT < SALELINE as a potential fantrap .

deepak115 :us: (BOB member since 2007-12-01)