Syntax to Map Virtual-Server's Character with Data-Group which Contains Pool Name

Consider first that the [virtual] command will return the name of the virtual server that is processing this iRule. It's a completely internal process, so there's no chance of a case mismatch. For example, if the virtual server name is literally:

mY_bIg-Ip_ViP    

then the [virtual] command will be guaranteed to return:

mY_bIg-Ip_ViP 

Given this fact, you shouldn't need to do a [string tolower ] evaluation. The following is more appropriate:

[class match [virtual] equals dg_parveez_dynamic_pools]

Where the [string tolower ] function would be important is anywhere the client could affect the value. So for example, let's say 5 different clients open their browsers and enter the following URI value (respectively):

/this-is-a-test-uri    
/This-is-a-test-uri    
/This-is-a-test-URI    
/This-Is-A-Test-Uri    
/ThIs-Is-A-tEsT-uRi    

In this case you have five different versions of the same URI. The backend server may not care about this, but iRule/TCL evaluations are case-sensitive. So to successfully match all 5 of these URIs, you must "normalize" the input.

if { [string tolower [HTTP::uri]] starts_with "/this-is-a-test-uri" }    

Notice that because you're normalizing the input to an all lowercase value, your match string must also be lowercase. The same applies to data group lookups.