Yield on an investment property is a factor of the annual rental value of the rental property (usually quoted in € / m2 per annum) divided by its current capital market value. In short, Yield = R / P X 100. Thus, the lower the yield the better rate of return on a property. Yield can also be used to calculate a property's current market value where you know rental levels, you can use this formula by substitution.
Unsurprisingly, lower yields are generally achieved in more central, desirable loactions (for example, a modern office in central Dublin will have a lower yield than say Blanchardstown). Prime retail in Dublin would be likely to be around 3%, with prime offices attracting maybe 4 - 4.5%. Industrial yield might be around the 5% mark.