Software Engineering - Ch. 5
What is illustrated in a UML sequence diagram?
A sequence of interactions between the actors in a system's environment and the objects in the system itself. The sequence of interactions describes the implementation of a system feature or function.
What are the principal components of a textual use-case description?
A tabular format seems to be the most useful when giving a description of the components in a use-case diagram. This is typically a simple textual description, a structured description in a table, or a sequence diagram. It usually includes actors which can be people or other systems, a description, a response, data, stimulus, and comments as well.
What UML diagram types do you need to represent the essential features of a system?
Activity diagrams, Use case diagrams, Sequence diagrams, Class diagrams, and State diagrams are all essential features of a system. Activity diagrams show the activities involved in a process. Use case show the interactions between a system and its environment. Sequence diagrams show interactions between actors and the system and between system components. Class diagrams show the object classes in the system and the associations between other classes. State diagrams show how the system reacts to internal and external events.
What perspectives should be used for developing models of a software system?
An external perspective should be used where you model the context or environment of the system. You should also have an interaction perspective, where you model the interactions between a system and its environment, or between the components of a system. It is also keen to have a structural perspective, where you model the organization of a system or the structure of the data that is processed by the system. Last but not least, a behavioral perspective, where you model the dynamic behavior of the system and how it responds to events.
What is described in a context model?
Context models are used to illustrate the operational context of a system - they show what lies outside the system boundaries. Social and organizational concerns may affect the decision on where to position system boundaries.
What is the basic assumption that underlies event-driven modelling?
It is based on the assumption that a system has a finite number of states and that events (stimuli) may cause a transition from one state to another. Event-driven modeling shows how a system responds to external and internal events.
How is generalization used to simplify the models of a system with many similar objects?
Often you will see generalization used in modeling systems by examining the classes in a system to see if there is scope for generalization. If changes are proposed, then you do not have to look at all classes in the system to see if they are affected by the change. Inheritance mechanisms are used in object-oriented languages to implement generalization. The attributes and operations with higher-level classes are also associated with the lower-level classes. The lower-level classes are subclasses that inherit the attribute and operations of their superclass. You can then add more specific attributes to the sub classes.
What are the claimed benefits of model-driven engineering?
The pros to model-driven engineering are that it allows systems to be considered at higher levels of abstraction and generating code automatically means that it is cheaper to adapt systems to new platforms.
What are the three types of abstract system model that are recommended by the MDA method?
There is the CIM (Computation Independent Model), PIM (Platform Independent Model), and the PSM (Platform Specific Model). CIMs show the important domain abstractions used in a system. CIMs are sometimes called domain models. PIMs show the operation of the system without reference to its implementation. The PIMs are usually described using UML models that show the static system structure and how it responds to external and internal events. PSMs are transformations of the platform-independent model with a separate PSM for each application platform. In principle, there may be layers of PSM, with each layer adding some platform-specific detail.
How are activity diagrams used in describing the context of use of a system?
They may be used to define business process models. They show activities in a process and the flow of control from one activity to another. The start of a process is indicated by a filled circle, the end by a filled circle inside another circle. Rectangles with round corners represent activities, that is, the specific subprocesses that must be carried out. You may include objects in activity charts. Arrows represent the flow of work from one activity to another, and a solid bar indicates activity coordination. When the flow from more than one activity leads to a solid bar, then all of these activities must be complete before progress is possible.