- An object diagram is an instance of a class diagram , where objects are replaced with classes. Object diagrams can be used to test class diagrams and its multiplicity.
- An Actor represents anything outside the system to which the system must conform to. An actor can be a person(he or she) a device , other machine etc.
- There can be many actors for one role as long as each actor has the same role. There can be many roles for one actor if the actor has many roles to olay in the system.
- Include relationships are used to model the relationships between use cases in which a base use case instance will always include the behaviour specified by a common use case. They are used to share common behaviour between use cases. They are denoted by arrows with the word include written. <<include>>
- Extend Relationships - Used to model the relationship between use cases in which a base use case instance may include the behaviour specified by an extending use case , subject to conditions. They are used to capture exceptional events .i.e. Some event may not take place but has the potential to. e.g. A booking systems for trains , customers may wish to book a sleeper if they are on the train for a long journey , not everyone will . This is an exceptional event . <<extend>>
- Generalisation - Sometimes there may be different versions of the same use case. There is a general case , then specialisations of this case. Generalistaion is often referred to as inheritance. Inheritance is intended to help reuse existing code with little or no modification. They are denoted with dashed lines and an arrowhead unfilled. E.g. You might have a general case - Person - and a specialist case of this - Student.