There are no parameters as such.
However, you can consider this there are some employees whom company employees on a regular basis and pays salaries. They are issued appointment letters etc. you can call them on roll employees.
Some employees are hired for day to day work for a day or a week, these are daily wage or casual workers.
Some employees are hirec through a contractor you pay the contractor a fixed amount and he disburses their salaries. These are Contract workers.
Hope the same is clear.
6th January 2011 From India, Pune