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SWE102-5-SYSTEM MODELING (Objectives of the chapter (understand why…
SWE102-5-SYSTEM MODELING
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Introduction
Model-driven engineering (MDE) is an approach to software development where models rather than programs are the principal outputs of the development process.
The programs that execute on a hardware/software platform are then generated automatically from the models
Proponents of MDE argue that this raises the level of abstraction in software engineering so that engineers no longer have to be concerned with programming language details or the specifics of execution platforms.
Usage
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Cons
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Savings from generating code may be outweighed by the costs
of developing translators for new platforms.
Model-driven engineering is still at an early stage of development, and it is unclear whether or not it will have a significant effect on software engineering practice.
Model-Driven Achitecture
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Agile Method and MDA
The developers of MDA claim that it is intended to support an iterative approach to development and so can be used within agile methods.
The notion of extensive up-front modeling contradicts the fundamental ideas in the agile manifesto and I suspect that few agile developers feel comfortable with modeldriven engineering.
If transformations can be completely automated and a complete program generated from a PIM, then, in principle, MDA could be used in an agile development process as no separate coding would be required.
Introduction
MDA is a model-focused approach to software design and implementation that uses a subset of UML models to describe a system.
Models at different levels of abstraction are created. From a high-level, platform independent model, it is possible, in principle, to generate a working program without manual intervention.
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Executable UML
Introduction
The fundamental notion behind model-driven engineering is that completely automated transformation of models to code should be possible.
This is possible using a subset of UML 2, called
Executable UML or xUML.
Features
3 keys type
Class models in which classes are defined, along with their
attributes and operations.
State models in which a state diagram is associated with each
class and is used to describe the life cycle of the class.
Domain models that identify the principal concerns in a system. They are defined using UML class diagrams and include objects, attributes and associations.
The dynamic behavior of the system may be specified declaratively using the object constraint language (OCL), or may be expressed using UML’s action language.
Introduction
Structural models of software display the organization of a system in terms of the components that make up that system and their relationships.
Structural models may be static models, which show the structure of the system design, or dynamic models, which show the organization of the system when it is executing.
You create structural models of a system when you are
discussing and designing the system architecture.
Class Diagram
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An association is a link between classes that indicates
that there is some relationship between these classes.
Class diagrams are used when developing an objectoriented system model to show the classes in a system and the associations between these classes.
When you are developing models during the early stages of the software engineering process, objects represent something in the real world, such as a patient, a prescription, doctor, etc.
Generalization
Introduction
Rather than learn the detailed characteristics of every entity that we experience, we place these entities in more general classes (animals, cars, houses, etc.) and learn the characteristics of these classes.
This allows us to infer that different members of these classes have some common characteristics e.g. squirrels and rats are rodents.
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Application
In modeling systems, it is often useful to examine 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.
In object-oriented languages, such as Java, generalization is implemented using the class inheritance mechanisms built into the language.
In a generalization, the attributes and operations associated with higher-level classes are also associated with the lower-level classes.
The lower-level classes are subclasses inherit the attributes and operations from their superclasses. These lower-level classes then add more specific attributes and operations.
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Process perspective
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Context models simply show the other systems in the environment, not how the system being developed is used in that environment.
Introduction
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Context models are used to illustrate the operational context of a system - they show what lies outside the system boundaries.
Introduction
user interaction, which involves user inputs and outputs, interaction between the system being developed and other systems or interaction between the components of the system
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User-Case Diagram
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Use cases were developed originally to support requirements elicitation and now incorporated into the UML.
Represented diagrammatically to provide an overview of
the use case and in a more detailed textual form.
Sequence Diagram
Sequence diagrams are part of the UML and are used to model the interactions between the actors and the objects within a system.
A sequence diagram shows the sequence of interactions that take place during a particular use case or use case instance.
The objects and actors involved are listed along the top of the diagram, with a dotted line drawn vertically from these.
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Introduction
Behavioral models are models of the dynamic behavior of a system as it is executing. They show what happens or what is supposed to happen when a system responds to a stimulus from its environment.
Two types of stimuli
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Event
Some event happens that triggers system processing. Events may have associated data, although this is not always the case.
Data-Driven Model
Data-driven models show the sequence of actions involved in processing input data and generating an associated output.
They are particularly useful during the analysis of requirements as they can be used to show end-to-end processing in a system.
Many business systems are data-processing systems that are primarily driven by data. They are controlled by the data input to the system, with relatively little external event processing.
Event-Driven Model
Introduction
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.
Real-time systems are often event-driven, with minimal data processing. For example, a landline phone switching system responds to events such as ‘receiver off hook’ by generating a dial tone.
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State Machine Model
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State machine models show system states as nodes and events as arcs between these nodes. When an event occurs, the system moves from one state to another
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- Introduction to system modeling
What is system modeling
System modelling helps the analyst to understand the functionality of the system and models are used to communicate with customers.
System modeling is the process of developing abstract models of a system, with each model presenting a different view or perspective of that system.
System modeling has now come to mean representing a system using some kind of graphical notation, which is now almost always based on notations in the Unified Modeling Language (UML).
System Perspectives
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 that is processed by the system.
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