Chasm Trap: Designing SAP BusinessObjects Universe

While designing SAP BusinessObjects universe with Universe Design Tool, Chasm Trap is one of the major join problems that one can come across.

We are in Chasm Trap when a table joins with two others in one-to-many relationship. Chasm Trap produces more data than expected.

Example

Consider the following ER diagram where DEPARTMENT is having 1-to-many relationships with EMPLOYEE and CONTRACT_STAFF tables.

Let’s assume we have following data in these tables.

image

BusinessObjects universe will produce something similar to the following query to join the above 3 tables:

select depart_name, employee_name, name "contract staff"
from department d
  inner join employee e on d.department_no = e.department_no
  inner join contract_staff c on c.department_no = d.department_no

Result of the query will have more rows than expected.

image

Resolution

Universe Design Tool doesn’t detect chasm traps automatically. They can be identified by visually inspecting the ER diagram.

Using Contexts

The recommended way of resolving Chasm Trap is to use contexts which will separate the two tables into separate contexts (employee and contract_stafff in our case). If both tables are used in the report, separate queries will be generated resulting in two tables in Web Intelligence report.

Using Derived Tables

Another approach which I have found handy in many cases is to use Derived Table functionality. Derived Table in universe designer can merge the two tables into one. Additional column containing record type can be introduced to still be able to tell the records apart (in our case, record type would be employee or contract_staff). This simplifies the design and avoids the Chasm Trap.

More at Official SAP BusinessObjects Universe Design Tool Guide

Git Push error: refusing to update checked out branch (Source Control)

Recently, I cloned a repository on my machine and made some changes to it. As I was pushing my changes back to the original repo, push failed with the error message:

“refusing to update checked out branch: refs/heads/master. By default, updating the current branch in a non-bare repository is denied…”

There are two things to note here in the error message. First the original repo is non-bare, secondly the push is to a branch which is currently checked out. Following are two possible ways to overcome the issue relating to bare repos and currently checked out branch.

Set Repository as ‘Bare’

Bare repositories do not have any working copy. Changes are not done directly to these repositories, rather changes are pushed from clones. Repositories hosted at GitHub are of this type.

One way to resolve the above issue is to make the repository ‘bare’. This can be done by running below command in original repo folder:

git config –bool core.bare true
 

Change the checked out branch

If you don’t want to convert your original repository to bare, another option is change the current branch. This can be done by:

git checkout
 

In case, there is only one branch in the repository, a temporary branch could be created and checked out:

git checkout -b temp
 

Once the push is executed, run the following commands to bring things back to original state:

git checkout master
git branch -d temp
 

Above will delete the temporary branch and checkout the master branch.

More at http://stackoverflow.com/questions/11117823/git-push-error-refusing-to-update-checked-out-branch