BOBJ - Chasm Traps (converging many to one joins)

About

Chasm Traps is see as

(convergence type ) which returns more data than expected by returning a cartesian product.

A chasm trap is a type of join path between three tables when two many-to-one joins converge on a single table, and there is no context in place that separates the converging join paths.

_

A chasm trap inflates results without warning

Example

The chasm trap causes a query to return every possible combination of rows for one measure with every possible combination of rows for the other measure.

Measure only on the first fact table _
Measure only on the second fact table _
Measures on the two fact tables return incorrect result (cartesian product) :
The query returns every possible combination of Number of Guests rows with every possible combination of Number of Future Guests rows: the Number of Guests transactions each appears twice, and the Number of Future Guests transactions each appears three times.
_

Detected by

  • Visual analysis of table schema.

Unlike BOBJ - Loops, chasm traps are not detected automatically by Business Object - Universe Designer, however, you can use Detect BOBJ - Context (Tools > Detect Contexts) to automatically detect and propose candidate contexts in your schema.

Solved by

  • Creating a BOBJ - Context.
  • Using the feature Multiple SQL statements for each measure. (File > Parameters > SQL tab )

_


Powered by ComboStrap