Work contract vs erection,commissioning & installation service

1. Works contract service is a composite contract of (sale + service ) i.e it involves transfer of property in goods and service in relation to te same . 2. Erectioning is a service provided by the service provider to service recipient for Erectioning of the plant or machinery or any other fixed asset. 3. Installation service is a service provided by the service provider to service recipient for installation of the fixed asset. By installation we mean putting the fixed asset into a condition ready for its use. 4. Commissioning is a testing service provided by the service provider to service recipient for checking and testing whether the fixed asset is in working condition or not ....post installation or Erection 5. Works contract is a material transfer + labour service whereas Erectioning , commissioning , installation is basically a service only .....

Thank u Harshal. U made concept so clear to me. I now just want to know that if contractor comes to me for filing his ST return . How should I determine that whether it is Erection, Commissioning & Installation Service or Work Contract Service ? What documents or evidences should I consider ?