If you are here for less than 183 days in your first year calendar year here then you will be taxed at a flat rate of 15%. If you are here more than 183 days then you will be taxed at resident rates (graduated tax rates).
http://www.iras.gov.sg/ESVPortal/iit/ii ... idents.asp
http://www.iras.gov.sg/ESVPortal/iit/ii ... gapore.asp
Or to put it differently If you arrive here after July 1, you will be taxed at 15% the first calendar year.
A foreigner will be regarded as resident in Singapore if he was physically present or exercising an employment in Singapore for 183 days or more during the year preceding the year of assessment in a capacity other than that of a director of a company.
The operative word here is physically present (which may not always mean you were working. - Your passport will show your date of entry & exit here. It does not mean necessarily consecutive days hence the reference to exercising an employment for 183 days (you may only work here but not necessarily reside here.)
Provided which you continue to work here all subsequent years you will be taxed at resident rates complete with resident tax deductions (few that they are) with the exception of CPF which you are not required to contribute. On the off chance that you employer does contribute (some do), because it is not required by law, it will be non-deductible.
Hope this helps to answer your questions.
sms