This paper proposes a new model that can represent the slot usage and the status of each possible slot groups in a flexible-grid optical network. This model facilitates visualizing the current network state in a graphical form as well as a proper data structure in the memory. It also promotes the design of new approaches for dynamic connection provisioning. The basic concepts of the model is illustrated for a single link first, then the same idea is used to generalize the model to represent the whole network topology. The usage of this model in routing and spectrum assignment is described by the update procedures on the structure after an addition or removal of a connection. This new model can reduce the time-complexity of existing routing and spectrum assignment methods by providing a data structure that captures the current spectrum usage of the network links.