The Object model should be represented as a combination of Collaboration and Sequence Diagrams as specified in IRR Use Cases P.28. You may also wish to use Object Interaction and Class Diagrams as described in RR P.1.32 and IRR Packages and Clasees P.13. Also object State Transition diagrams as needed and described in IRR Object Behavior P.2. See IRR Relationships P.2, SOM 16.4 P.302, SOM Fig. 14.16 P.265 for further details on relationships and object interaction diagrams.
Operations are specific tasks that define how a behavior is carried out within the system.
That is, behaviors are broken down into sets of operations. This may require the addition of purely design operations that do not have direct counterparts in the domain. This differentiates operations from behaviors. Leaf behaviors are called operations when they directly act upon some form of data. Operations are either events or policies that have fundamentally different implementation strategies but both which eventually end up as operations.