Dealing with constrained values during your data migration and, to a lesser extent, your data integration activity, is a common headache that you will have to deal with. The Talend Framework aims to make this easy for you, with the library Job LibLoadCVMap.
In simple terms, you have a constrained list of values in your source system (unfortunately, this constrained list is often free-text) and you need to map these to the constrained values in your target system. The value lists will often contain different codes that actually mean the same thing.
The library Job LibLoadCVMap takes responsibility for loading and pre-processing your constrained value mapping tables, presenting sanitised look-ups that you may use in your Job.
If there are inconsistencies in your constrained value mapping input, these will be reported and may allow processing to be stopped.