dependent in practice. In general, the hard priority optimization may be appropriate for problems with well-defined goals in order to avoid stagnation with unfeasible goal settings. Soft priority optimization is more suitable for applications where moderate performance among various objective components is desired. Besides soft/hard priority information, there may be additional specifications such as optimization constraints that are required to be satisfied in the optimization. These specifications could be easily incorporated in MO optimization by formulating the constraints as additional objective components to be optimized (Fonseca & Fleming, 1998). This will be discussed in the next section. 

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## 2.3 Optimization With Soft And Hard Constraints

Constraints often exist in practical optimization problems (Luus et al. 1995; Michalewicz & Schoenauer, 1996). These constraints are often incorporated in the MO optimization function as 