Software Engineering-Unit 4 "Architectural Design" by Adi.pdf

ARCHITECTURAL DESIGN
DR. K. ADISESHA

Software Engineering
Unit-4 Introduction
Architectural Design
Architectural Models
Architectural patterns
OOD using UML
2
ARCHITECTURAL DESIGN
&
IMPLEMENTATION
Dr. K. Adisesha

Introduction
Dr. K. Adisesha
3
Architectural Design:
Architectural design (also called system design), which acts as a preliminary ‘blueprint’
from which software can be developed.
➢ IEEE defines Architectural design as “The process of defining a collection of hardware
and software components and their interfaces to establish the framework for the
development of a computer system.”
➢ This framework is established by examining the software requirements document and
designing a model for providing implementation details.
➢ These details are used to specify the components of the system along with their inputs,
outputs, functions, and the interaction between them.

Introduction
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Architectural Design:
The software that is built for computer-based systems can exhibit one of these many
architectural styles.
➢ Each style will describe a system category that consists of :
❖ A set of components(eg: a database, computational modules) that will perform a
function required by the system.
❖ The set of connectors will help in coordination, communication, and cooperation
between the components.
❖ Conditions that how components can be integrated to form the system.
❖ Semantic models that help the designer to understand the overall properties of the
system.

Introduction
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Architectural design:
Architectural design is a process for identifying the sub-systems making up a system
and the framework for sub-system control and communication.
➢ Software architectures can be designed at two levels of abstraction:
❖ Architecture in the small: is concerned with the architecture of individual
programs. At this level, we are concerned with the way that an individual program
is decomposed into components.
❖ Architecture in the large: is concerned with the architecture of complex enterprise
systems that include other systems, programs, and program components. These
enterprise systems are distributed over different computers, which may be owned
and managed by different companies.

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Architectural Design Representation:
Architectural design can be represented using the following models:
➢ Structural model: Illustrates architecture as an ordered collection of program components
➢ Dynamic model: Specifies the behavioral aspect of the software architecture and indicates
how the structure or system configuration changes as the function changes due to change
in the external environment.
➢ Process model: Focuses on the design of the business or technical process, which must be
implemented in the system.
➢ Functional model: Represents the functional hierarchy of a system.
➢ Framework model: Attempts to identify repeatable architectural design patterns
encountered in similar types of application. This leads to an increase in the level of
abstraction.

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Architectural Design Output:
The architectural design process results in an Architectural Design Document consists
of a number of graphical representations that comprises software models along with
associated descriptive text.
➢ Architectural design document gives the developers a solution to the problem stated in the
Software Requirements Specification (SRS).
➢ In addition to ADD, other outputs of the architectural design are listed below.
❖ Various reports including audit report, progress report, and configuration status accounts
report and various plans for detailed design phase, which include the following:
▪ Software verification and validation plan
▪ Software configuration management plan
▪ Software quality assurance plan
▪ Software project management plan.

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Advantages of Architectural Design:
Three advantages of explicitly designing and documenting software architecture:
➢ Stakeholder communication: Architecture may be used as a focus of discussion by
system stakeholders.
➢ System analysis: Well-documented architecture enables the analysis of whether the
system can meet its non-functional requirements.
➢ Large-scale reuse: The architecture may be reusable across a range of systems or
entire lines of products.
❖ Pros: simple, useful for communication with stakeholders, great for project planning.
❖ Cons: lack of semantics, types of relationships between entities, visible properties of
entities in the architecture.

Architectural design
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Uses of architectural models:
Software architecture is most often represented using simple, informal block diagrams
showing entities and relationships.
➢ As a way of facilitating discussion about the system design
❖ A high-level architectural view of a system is useful for communication with system
stakeholders and project planning because it is not cluttered with detail.
❖ Stakeholders can relate to it and understand an abstract view of the system.
❖ They can then discuss the system as a whole without being confused by detail.
➢ As a way of documenting an architecture that has been designed
❖ The aim here is to produce a complete system model that shows the different
components in a system, their interfaces and their connections.

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Architectural design decisions:
Architectural design is a creative process so the process differs depending on the type
of system being developed.
➢ However, a number of common decisions span all design processes and these decisions
affect the non-functional characteristics of the system:
❖ Is there a generic application architecture that can be used?
❖ How will the system be distributed?
❖ What architectural styles are appropriate?
❖ What approach will be used to structure the system?
❖ How will the system be decomposed into modules?
❖ What control strategy should be used?
❖ How will the architectural design be evaluated?
❖ How should the architecture be documented?

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Architectural design decisions:
The architecture of a system may be designed around one of more architectural
patterns/styles, which capture the essence of an architecture and can be instantiated in
different ways.
➢ The particular architectural style should depend on the non-functional system
requirements:
❖ Performance: localize critical operations and minimize communications. Use large rather
than fine-grain components.
❖ Security: use a layered architecture with critical assets in the inner layers.
❖ Safety: localize safety-critical features in a small number of sub-systems.
❖ Availability: include redundant components and mechanisms for fault tolerance.
❖ Maintainability: use fine-grain, replaceable components.

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Architectural views:
Each architectural model only shows one view or perspective of the system. It might
show how a system is decomposed into modules, how the run-time processes interact or
the different ways in which system components are distributed across a network.
➢ 4+1 view model of software architecture:
❖ A logical view: which shows the key abstractions in the system as objects or object classes.
❖ A process view: which shows how, at run-time, the system is composed of interacting
processes.
❖ A development view: which shows how the software is decomposed for development.
❖ A physical view: which shows the system hardware and how software components are
distributed across the processors in the system.
❖ Related using use cases or scenarios (+1).

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Architectural Patterns:
An architectural pattern is a stylized description of a good design practice, which has
been tried and tested in different environments.
➢ Patterns are a means of representing, sharing and reusing knowledge.
➢ Patterns should include information about when they are and when the are not useful.
Patterns may be represented using tabular and graphical descriptions.
➢ Various Architectural patterns are listed below:
❖ Model-View-Controller
❖ Layered Architecture
❖ Repository Architecture
❖ Client-server Architecture
❖ Pipe and filter Architecture

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Model-View-Controller (MVC):
Serves as a basis of interaction management in many web-based systems. The display
presented to the user frequently changes over time in response to input or computation.
➢ Supported by most language frameworks.
➢ Decouples three major interconnected components:
❖ The Model is the central component of the pattern that directly manages the data,
logic and rules of the application. It is the application's dynamic data structure,
independent of the user interface.
❖ A View can be any output representation of information, such as a chart or a
diagram. Multiple views of the same information are possible.
❖ The Controller accepts input and converts it to commands for the model or view.

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The display presented to the user frequently changes over time in response to input or
computation. Different users have different needs for how they want to view the
program
➢ The system is structured into three logical components that interact with each other.
❖ The Model component manages the system data and
associated operations on that data.
❖ The View component defines and manages how the
data is presented to the user.
❖ The Controller component manages user interaction
(e.g., key presses, mouse clicks, etc.) and passes these
interactions to the View and the Model.

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Separates presentation and interaction from the system data. The system is structured
into three logical components that interact with each other.
➢ Advantages:
❖ Views and Controllers can be easily be added, removed, or changed during
execution. User interface components can be changed, even at runtime.
➢ Disadvantages:
❖ Views and Controller are often hard to separate; frequent updates may slow data
display and degrade user interface performance.
❖ The MVC style makes user interface components (views, controllers) highly
dependent on model components.

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Layered Architecture:
Organizes the system into layers with related functionality associated with each layer. A
layer provides services to the layer above it so the lowest-level layers represent core
services that are likely to be used throughout the system.
➢ Used to model the interfacing of sub-systems.
➢ Organizes the system into a set of layers (or abstract machines) each of which provide
a set of services.
➢ Supports the incremental development of sub-systems in different layers. When a layer
interface changes, only the adjacent layer is affected.
➢ However, often artificial to structure systems in this way.

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Layered Architecture:
Used when building new facilities on top of existing systems; when the development is
spread across several teams with each team responsibility for a layer of functionality;
when there is a requirement for multi-level security.
➢ Advantages:
❖ Allows replacement of entire layers so long
as the interface is maintained.
❖ Redundant facilities (e.g., authentication)
can be provided in each layer to increase
the dependability of the system.

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Repository Architecture:
All data in a system is managed in a central repository that is accessible to all system
components. Components do not interact directly, only through the repository.
➢ Sub-systems must exchange data. This may be done in two ways:
❖ Shared data is held in a central database or repository and may be accessed by all
sub-systems;
❖ Each sub-system maintains its own database and passes data explicitly to other
sub-systems.
➢ When large amounts of data are to be shared, the repository model of sharing is most
commonly used, this is an efficient data sharing mechanism.

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Repository Architecture:
Use this pattern when you have a system in which large volumes of information are
generated that has to be stored for a long time. You may also use it in data-driven
systems where the inclusion of data in the repository triggers an action or tool.
➢ Advantages:
❖ Components can be independent-they do not need
to know of the existence of other components.
Changes made by one component can be
propagated to all components.
❖ All data can be managed consistently (e.g.,
backups done at the same time) as it is all in one
place.

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Client-Server Architecture:
In a client-server architecture, the functionality of the system is organized into services,
with each service delivered from a separate server. Clients are users of these services
and access servers to make use of them.
➢ Distributed system model which shows how data and processing is distributed across a
range of components, but can also be implemented on a single computer.
➢ Set of stand-alone servers which provide specific services such as printing, data
management, etc.,
➢ Set of clients which call on these services.
➢ Network which allows clients to access servers.

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Client-server Architecture:
Used when data in a shared database has to be accessed from a range of locations.
Because servers can be replicated, may also be used when the load on a system is
variable.
➢ Advantages:
❖ The principal advantage of this model is that
servers can be distributed across a network.
❖ General functionality (e.g., a printing service)
can be available to all clients and does not
need to be implemented by all services.

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Pipe and filter Architecture:
The processing of the data in a system is organized so that each processing component
(filter) is discrete and carries out one type of data transformation.
➢ The data flows (as in a pipe) from one component to another for processing.
➢ Functional transformations process their inputs to produce outputs.
➢ May be referred to as a pipe and filter model (as in UNIX shell).
➢ Variants of this approach are very common. When transformations are sequential, this
is a batch sequential model which is extensively used in data processing systems.
➢ Not really suitable for interactive systems.

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Pipe and filter Architecture:
Commonly used in data processing applications (both batch- and transaction-based)
where inputs are processed in separate stages to generate related outputs.
➢ Advantages:
❖ Easy to understand and supports
transformation reuse.
❖ Workflow style matches the structure of many
business processes.
❖ Evolution by adding transformations is
straightforward.
❖ Can be implemented as either a sequential or
concurrent system.

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Application Architectures:
A generic application architecture is an architecture for a type of software system that
may be configured and adapted to create a system that meets specific requirements.
➢ Application systems are designed to meet an organizational need.
➢ As businesses have much in common, their application systems also tend to have a
common architecture that reflects the application requirements.
➢ Application architectures can be used as a:
❖ Starting point for architectural design.
❖ Design checklist.
❖ Way of organizing the work of the development team.
❖ Means of assessing components for reuse.
❖ Vocabulary for talking about application types.

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Application Architectures:
As businesses have much in common, their application systems also tend to have a
common architecture that reflects the application requirements.
➢ Examples of application types:
❖ Data processing applications: Data driven applications that process data in batches
without explicit user intervention during the processing.
❖ Transaction processing applications: Data-centred applications that process user
requests and update information in a system database.
❖ Event processing systems: Applications where system actions depend on interpreting
events from the system's environment.
❖ Language processing systems: Applications where the users' intentions are specified in
a formal language that is processed and interpreted by the system.

OOD using UML
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Object-Oriented Design using UML:
Structured object-oriented design processes involve developing a number of different
system models.
➢ They require a lot of effort for development and maintenance and, for small systems,
this may not be cost-effective.
➢ Common activities in these processes include:
❖ Define the context and modes of use of the system
❖ Design the system architecture
❖ Identify the principal system objects
❖ Develop design models
❖ Specify object interfaces

OOD using UML
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Object-Oriented Design using UML:
Object-Oriented Design is a software development approach to design and implement
software system as a collection of interacting stateful objects with specified structure
and behavior.
➢ We will take a look at some of OOD concepts that seem relevant to the UML:
❖ Classes, Object
❖ Interface
❖ Collaboration
❖ Use case
❖ Active classes
❖ Components
❖ Nodes

OOD using UML
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Structural Things using UML:
Graphical notations used in structural things are most widely used in UML. These are
considered as the nouns of UML models.
Interface Notation Use Case Notation
Class & Object Notation
Actor Notation
Initial State Notation Final State Notation
Active Class Notation
Component Notation

OOD using UML
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Structural Things using UML:
Graphical notations used in structural things are most widely used in UML. These are
considered as the nouns of UML models.
➢ Class & Object Notation: UML Classes are used to represent objects. Objects can be anything
having properties and responsibility. The diagram is divided into four parts.
➢ Interface Notation: Interface is used to describe the functionality without implementation.
Interface is represented by a circle.
➢ Use Case Notation: Use case is used to capture high level functionalities of a system. Use case
is represented as an eclipse with a name inside it.
➢ Actor Notation: An actor can be defined as some internal or external entity that interacts with
the system.
➢ Initial State Notation: Initial state is defined to show the start of a process.
➢ Final State Notation: Final state is used to show the end of a process.

OOD using UML
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System context and interactions:
Understanding the relationships between the software that is being designed and its
external environment is essential for deciding how to provide the required system
functionality and how to structure the system to communicate with its environment.
➢ Understanding of the context also lets you establish the boundaries of the system.
➢ Setting the system boundaries helps you decide what features are implemented in the
system being designed and what features are in other associated systems.
❖ A system context is a structural model (e.g., a class diagram) that demonstrates the
other systems in the environment of the system being developed.
❖ An interaction model is a dynamic model (e.g., a use case diagram + structured
natural language description) that shows how the system interacts with its
environment as it is used.

OOD using UML
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Weather station:
The weather information system establishes a satellite communication link with the
weather station and requests transmission of the data.
➢ Understanding of the context also lets you establish the boundaries of the system
➢ Use case: Report weather Actors:Weather information system, Weather station

OOD using UML
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Weather station:
The weather information system establishes a satellite communication link with the
weather station and requests transmission of the data.
System Weather station
Use case Report weather
Actors Weather information system, Weather station
Description
The weather station sends a summary of the weather data that has been collected from the instruments in the
collection period to the weather information system. The data sent are the maximum, minimum, and average
ground and air temperatures; the maximum, minimum, and average air pressures; the maximum, minimum,
and average wind speeds; the total rainfall; and the wind direction as sampled at five-minute intervals.
Stimulus
The weather information system establishes a satellite communication link with the weather station and
requests transmission of the data.
Response The summarized data is sent to the weather information system.
Comments
Weather stations are usually asked to report once per hour but this frequency may differ from one station to
another and may be modified in the future.

OOD using UML
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Once interactions between the system and its environment have been understood, you
use this information for designing the system architecture.
➢ You identify the major components that make up the system and their interactions, and
then may organize the components using an architectural pattern (e.g. a layered or client-
server model).

OOD using UML
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Identifying object classes is often a difficult part of object oriented design. There is no
'magic formula' for object identification.
➢ It relies on the skill, experience and domain knowledge of system designers.
➢ Object identification is an iterative process. You are unlikely to get it right first time.
➢ Approaches to object identification include:
❖ Use a grammatical approach based on a natural language description of the system.
❖ Base the identification on tangible things in the application domain.
❖ Use a behavioral approach and identify objects based on what participates in what
behavior.
❖ Use a scenario-based analysis. The objects, attributes and methods in each scenario
are identified.

Discussion
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Queries ?
Prof. K. Adisesha
9449081542
Reference: Sommerville, Software Engineering, 10 ed.,

Software Engineering-Unit 4 "Architectural Design" by Adi.pdf

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