Use cases have been applied to describe how a web service will is used. Use cases can be categorized into classes of usage scenarios, which are often then defined as sequences of actions for accomplishing specific tasks. Neither use case nor scenario is not Object-Oriented (OO). For a web service to be implemented with OO programming technique(s), adopting object concept to system specifications from the scenarios can reduce the experience dependency on platforms transition. The paper proposes a model, named Object Oriented Petri Nets with modularity (OOMPNets), which introduces Colored Petri Nets into OO techniques. Based on the scenario, OOMPNets can be allowed to describe objects incrementally. Besides, the analysis techniques based on Colored Petri Nets can be applied for that of OOMPNets to reduce the effects of specification errors.