APP DEV: System Modeling

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

representing a

system using some kind of graphical notation, which is

now almost always based on notations in the Unified

Modeling Language (UML).

System modelling

helps the analyst to understand the

functionality of the system and models are used to

communicate with customers.

Models of the existing system

are used during requirements

engineering. They help clarify what the existing system does

and can be used as a basis for discussing its strengths and

weaknesses. These then lead to requirements for the new

system.

An external perspective

where you model the context or

environment of the system.

An interaction perspective

where you model the

interactions between a system and its environment, or

between the components of a system.

A structural perspective

where you model the

organization of a system or the structure of the data that

is processed by the system.

A behavioral perspective

where you model the dynamic

behavior of the system and how it responds to events.

Activity diagrams

which show the activities involved in a

process or in data processing .

Use case diagrams

which show the interactions

between a system and its environment.

Sequence diagrams

which show interactions between

actors and the system and between system components.

Class diagrams

which show the object classes in the

system and the associations between these classes.

State diagrams

which show how the system reacts to

internal and external events.

True

Incomplete and incorrect models are OK as their role is to

support discussion.

T/F

False

Models should be an accurate representation of the system but

needs to be complete.

T/F

True

Models have to be both correct and complete.

T/F

Context models

are used to illustrate the operational

context of a system - they show what lies outside the

system boundaries.

System boundaries

are established to define what is

inside and what is outside the system.

True

Context models simply show the other systems in the

environment, not how the system being developed is

used in that environment.

T/F

Process models

reveal how the system being developed

is used in broader business processes.

TRUE

Modeling user interaction is important as it helps to

identify user requirements.

T/F

False

Modeling system-to-system interaction can not highlights the

communication problems that may arise.

Modeling component interaction

helps us understand if a

proposed system structure is likely to deliver the required

system performance and dependability.

Use case diagrams and sequence diagrams

_____ and _____ may be

used for interaction modeling.

use case

represents a discrete task that involves

external interaction with a system.

Use Case Modeling

Represented diagramatically to provide an overview of

the use case and in a more detailed textual form.

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.

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.

Class diagrams

are used when developing an

object-oriented system model to show the classes in a

system and the associations between these classes.

An association

is a link between classes that indicates

that there is some relationship between these classes.

Generalization

is an everyday technique that we use to

manage complexity.

Generalization

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.

generalization

In object-oriented languages, such as Java, ____ 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.

An aggregation model

shows how classes that are

collections are composed of other classes.

Aggregation models

are similar to the part-of relationship

in semantic data models.

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.

Data Driven Modeling

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

Data-driven models

show the sequence of actions

involved in processing input data and generating an

associated output.

Data-driven models

They are particularly useful during the analysis of

requirements as they can be used to show end-to-end

processing in a system.

Event Driven Modeling

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.

Event-driven modeling

shows how a system responds to

external and internal events.

Event Driven Modeling

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.

State machine models

These model the behaviour of the system in response to

external and internal events.

State machine models

They show the system’s responses to stimuli so are

often used for modelling real-time systems.

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.

Model-driven engineering (MDE)

is an approach to

software development where models rather than

programs are the principal outputs of the development

process.

Model-driven engineering (MDE)

The programs that execute on a hardware/software

platform are then generated automatically from the

models.

model-driven engineering

Pros

Allows systems to be considered at higher levels of abstraction

Generating code automatically means that it is cheaper to adapt

systems to new platforms.

model-driven engineering

Cons

Models for abstraction and not necessarily right for

implementation.

Savings from generating code may be outweighed by the costs

of developing translators for new platforms.

Model-driven architecture (MDA)

was the precursor of

more general model-driven engineering

Model-driven architecture MDA

is a model-focused approach to software design

and implementation that uses a subset of UML models to

describe a system.

Model-driven architecture MDA

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.

A computation independent model (CIM)

These model the important domain abstractions used in a

system. CIMs are sometimes called domain models.

A platform independent model (PIM)

These model the operation of the system without reference to its

implementation. The ___ is usually described using UML models

that show the static system structure and how it responds to

external and internal events.

Platform specific models (PSM)

These 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.

Agile methods 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.

Executable UML or xUML.

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

_____