Chapter 5 System modeling.

Use of graphical models.

A way to stimulate and focus discussion about an existing or proposed system. A way of documenting an existing system. As a detailed system description that can be used to generate a system implementation.

Interaction models.

All systems involve interaction of some kind. This can be user interaction, which involves user inputs and outputs. Here we can find use case modeling and sequence diagrams.

Benefits of model-based engineering.

Allows engineers to think about systems at a high level of abstraction, without concern for the details of their implementation. This reduces the likehood of errors, speeds up the design and implementation process, and allows for the creation of reusable, platform-independent application models.

Behavioral models.

Are models of the dynamic behavior of a system as it is executing. They show what happends or what is supposed to happen when a system responds to a stimulus from its environment. These stimuli may be either data or events.

Sequence models.

Are primarily used in the UML to model the interaction between the actors and the objects in a system and the interactions between the objects themselves.

Platform-specific models (PSM).

Are transformations of the platform independent model with a seperate model for each application platform. In principle, there may be layers of the model, with each layer adding some platform-specific detail.

Context model.

At an early stage in the specification of a system, you should decide on the system boundaries, that is, on what is and is not part of the system being developed. In some cases the boundary between a system and its environment is relatively clear. In other cases, there is more flexibility.

Structural models.

Displays the organization of a system in terms of the components that make up that system and their relationships. They may be static or dynamic. You create them when you are discussing and designing the system architecture.

Model-driven architecture.

Is a model-focused approach to software design and implementation that uses a subset of UML models to describe a system.

Model-driven engineering (MDE)

Is an approach to software development whereby models rather than programs are the principal outputs of the development process. The programs that execute on a hardware/software platform are generated automatically from the models.

Generalization.

Is an everyday technique that we use to manage complexity. Rather than learn the detailed characteristics of everything that we experience, we learn about general classes and learn the characteristics of these classes.

System modeling.

Is the process of developing abstract models of a system, with each model presenting a different view or perspective of that system.

A computation independent model (CIM).

Model the importaint domain abstractions used in a system and so are sometimes called domain models. You may develop several different models, reflecting different views of the system.

A platform-independent model (PIM).

Model the operation of the system without reference to its implementation. This model is usually described using UML models that show the static system structure and how it responds to external and internal events.

Aggregation.

Objects in the real world are often made up of different parts. In UML this is a special type of association between classes, which means that one object is composed of other objects.

Event-driven modeling.

Shows how a system responds to external and internal events. 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.

Data-driven modeling.

Shows the sequence of actions involved in processing input data and generating an associated output. They can be used during the analysis of requirements, as they show end-to-end processing in a system.

Models.

These are used during the requirements engineering process to help derive the detailed requirements for a system, during the design process to describe the system to engineers implementing the system, and after implementation to document the system's structure and operation.

Class diagrams.

They are used when developing an object-oriented system model to show the classes in a system and the associations between these classes. Loosely, an object class can be thought of as a general definition of one kind of system object.

Use case

This can be taken as a simple description of what a user expects from a system in that interaction. Diagrams of this give a simple overview of an interaction, and you need to add more detail for complete interaction description.

External perspective.

Where you model the context or environment of the system.

Behavioral perspective.

Where you model the dynamic behaviour of the system and how it responds to events.

Interaction perspective.

Where you model the interactions between a system and its environment, or between the components of a system.

Structural perspective.

Where you model the organization of a system or the structure of the data processed by the system.