Reverse Concatenation

Webi Variable Question:

Have a field that is a concatenation of values separated by comma. The field values are variable in length. Values are returned from a BI Universe to Webi.

field1, field12, field3, field1234, f5, f67

Using the POS function I can determine the first position for the first comma. How can I determine the field locations of variable length? I want a variable for each data point.

var1= Field1

var2= Field12

var3= Field3 and so on.

Assume use of SUBSTR, POS, LEN, RIGHT, LEFT although in what context?