CurrentMonth can be calculated by a sql statement.
Note:
REPOSITORY VARIABLE(DYNAMIC)
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Initialized when BI server is started
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Assigned value dynamically based on the result of a query
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Value is dependent of the sql provided in Initialization Block
Create a dynamic variable and provide a Name and Default Initializer.Create a new initialization block by clicking on the New button in the above screen.

http://www.adivaconsulting.com/images/blog/OBIEE_Variable_files/image003.jpg Provide Intialization Block variable Name

http://www.adivaconsulting.com/images/blog/OBIEE_Variable_files/image004.jpg
Click on "Edit Data Source" button and provide the sql to be used for the variable, e.g.
select lower(sys_context('USERENV','SESSION_USER'))|| '@'|| lower(sys_context('USERENV','DB_NAME'))
from dual;

Open up the Administration tool, go to Manage then variables.
See screenshot below.

Then follow this picture to create a new Initialization Block.

Name your Initialization block init_block_test.

Explanation
Denormalized data in the transactional system could be divided into different tables to increase performance.

Explanation/Reference:
Steps to Create a Dimension Hierarchy - >
Create a dimension object.
Add a parent-level object.
Add child-level objects.
Determine number of elements.
Specify level columns.
Create level keys.
Create a level-based measure.
Create additional level-based measures.
Create share measures.
Create rank measures.
Add measures to Presentation layer.
Test share and rank measures.