BOBJ - Chasm Traps (converging many to one joins)
1 - About
Chasm Traps is see as
- a Join Path problem or
(convergence type ) which returns more data than expected by returning a cartesian product.
A chasm trap inflates results without warning
2 - Articles Related
3 - 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.
4 - Detected by
- Visual analysis of table schema.
5 - Solved by
- Creating a BOBJ - Context.
- Using the feature Multiple SQL statements for each measure. (File > Parameters > SQL tab )