Software Engineering:

Architectural Design

Dr. Hassan Eldeeb

Assist. Professor of Computers Engineering
Tanta University, Tanta, Egypt
hassan.eldeeb@f-eng.tanta.edu.eg

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025 1
Topics covered
✧ Architectural design decisions

✧ Architectural views

✧ Architectural patterns

✧ Application architectures

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Architectural design
✧ Architectural design is concerned with understanding how a software system should be
organized and designing the overall structure of that system.

✧ Architectural design is the critical link between design and requirements engineering, as it
identifies the main structural components in a system and the relationships between them.

✧ The output of the architectural design process is an architectural model that describes how
the system is organized as a set of communicating components.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Agility and architecture
✧ It is generally accepted that an early stage of agile processes is to design an overall systems
architecture.

✧ Refactoring the system architecture is usually expensive because it affects so many

components in the system

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
The architecture of a packing robot control system

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Architectural 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.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Advantages of explicit architecture
● Stakeholder communication
○ Architecture may be used as a focus of discussion by system stakeholders.

● System analysis
○ Means that analysis of whether the system can meet its non-functional requirements is possible.

● Large-scale reuse
○ The architecture may be reusable across a range of systems
○ Product-line architectures may be developed.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Architectural representations
✧ Simple, informal block diagrams showing entities and relationships are the most frequently
used method for documenting software architectures.

✧ But these have been criticised because they lack semantics, do not show the types of
relationships between entities nor the visible properties of entities in the architecture.

✧ Depends on the use of architectural models.The requirements for model semantics depends
on how the models are used.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Box and line diagrams
✧ Very abstract - they do not show the nature of component relationships nor the externally
visible properties of the sub-systems.

✧ However, useful for communication with stakeholders and for project planning.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Use of architectural models
✧ 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.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
 Architectural design decisions

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
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.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Architectural design decisions

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Architecture reuse
✧ Systems in the same domain often have similar architectures that reflect domain concepts.

✧ Application product lines are built around a core architecture with variants that satisfy
particular customer requirements.

✧ The architecture of a system may be designed around one of more architectural patterns or
‘styles’.
○ These capture the essence of an architecture and can be instantiated in different ways.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Architecture and system characteristics
● Performance
○ Localise critical operations and minimise communications. Use large rather than fine-grain
components.
● Security
○ Use a layered architecture with critical assets in the inner layers.
● Safety
○ Localise 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.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
 Architectural views

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Architectural views
✧ What views or perspectives are useful when designing and documenting a system’s
architecture?

✧ What notations should be used for describing architectural models?

✧ 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. For both design and documentation, you
usually need to present multiple views of the software architecture.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Architectural views

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
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)

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Representing architectural views
✧ Some people argue that the Unified Modeling Language (UML) is an appropriate notation for
describing and documenting system architectures

✧ I disagree with this as I do not think that the UML includes abstractions appropriate for
high-level system description.

✧ Architectural description languages (ADLs) have been developed but are not widely used

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
 Architectural patterns

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Architectural patterns
✧ Patterns are a means of representing, sharing and reusing knowledge.

✧ An architectural pattern is a stylized description of good design practice, which has been
tried and tested in different environments.

✧ Patterns should include information about when they are and when the are not useful.

✧ Patterns may be represented using tabular and graphical descriptions.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
The Model-View-Controller (MVC) pattern
Name MVC (Model-View-Controller)

Description Separates presentation and interaction from the system data. 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. See Figure
6.3.

Example Figure 6.4 shows the architecture of a web-based application system organized using the MVC
pattern.
When used Used when there are multiple ways to view and interact with data. Also used when the future
requirements for interaction and presentation of data are unknown.

Advantages Allows the data to change independently of its representation and vice versa. Supports
presentation of the same data in different ways with changes made in one representation shown
in all of them.
Disadvantages Can involve additional code and code complexity when the data model and interactions are
simple.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
The organization of the Model-View-Controller

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Web application architecture using the MVC pattern

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Layered architecture
✧ Used to model the interfacing of sub-systems.
✧ Organises 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.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
The Layered architecture pattern
Name Layered architecture
Description 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. See
Figure 6.6.
Example A layered model of a system for sharing copyright documents held in different
libraries, as shown in Figure 6.7.
When used 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.
Disadvantages In practice, providing a clean separation between layers is often difficult and a
high-level layer may have to interact directly with lower-level layers rather than
through the layer immediately below it. Performance can be a problem because
of multiple levels of interpretation of a service request as it is processed at each
layer.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
A generic layered architecture

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
The architecture of the iLearn system

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Repository architecture
● 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 a this is an efficient data sharing mechanism.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
The Repository pattern
Name Repository
Description 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.
Example Figure 6.9 is an example of an IDE where the components use a repository of
system design information. Each software tool generates information which is
then available for use by other tools.
When used You should 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.
Disadvantages The repository is a single point of failure so problems in the repository affect
the whole system. May be inefficiencies in organizing all communication
through the repository. Distributing the repository across several computers
may be difficult.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
A repository architecture for an IDE

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Client-server architecture
● Distributed system model which shows how data and processing is distributed across a
range of components.
○ Can 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.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
The Client–server pattern
Name Client-server
Description 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.
Example Figure 6.11 is an example of a film and video/DVD library organized as a client–server
system.
When used 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.
Disadvantages Each service is a single point of failure so susceptible to denial of service attacks or
server failure. Performance may be unpredictable because it depends on the network
as well as the system. May be management problems if servers are owned by
different organizations.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
A client–server architecture for a film library

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Pipe and filter architecture
● 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.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
The pipe and filter pattern
Name Pipe and filter
Description 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.
Example Figure 6.13 is an example of a pipe and filter system used for processing invoices.
When used 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.
Disadvantages The format for data transfer has to be agreed upon between communicating
transformations. Each transformation must parse its input and unparse its output to the
agreed form. This increases system overhead and may mean that it is impossible to
reuse functional transformations that use incompatible data structures.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
An example of the pipe and filter architecture used in a payments
system

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
 Application architectures

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Application architectures
✧ Application systems are designed to meet an organisational need.

✧ As businesses have much in common, their application systems also tend to have a common
architecture that reflects the application requirements.

✧ 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.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Use of application architectures
● As a starting point for architectural design.

● As a design checklist.

● As a way of organising the work of the development team.

● As a means of assessing components for reuse.

● As a vocabulary for talking about application types.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
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.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Application type examples
● Two very widely used generic application architectures are transaction
processing systems and language processing systems.
● Transaction processing systems
○ E-commerce systems;
○ Reservation systems.
● Language processing systems
○ Compilers;
○ Command interpreters.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Transaction processing systems
● Process user requests for information from a database or requests to update the database.

● From a user perspective a transaction is:

○ Any coherent sequence of operations that satisfies a goal;
○ For example - find the times of flights from London to Paris.

● Users make asynchronous requests for service which are then processed by a transaction
manager.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
The structure of transaction processing applications

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
The software architecture of an ATM system

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Information systems architecture
✧ Information systems have a generic architecture that can be organised as a layered architecture.

✧ These are transaction-based systems as interaction with these systems generally involves database
transactions.

✧ Layers include:

○ The user interface

○ User communications

○ Information retrieval

○ System database

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Layered information system architecture

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
The architecture of the Mentcare system

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Web-based information systems
✧ Information and resource management systems are now usually web-based systems where
the user interfaces are implemented using a web browser.

✧ For example, e-commerce systems are Internet-based resource management systems that
accept electronic orders for goods or services and then arrange delivery of these goods or
services to the customer.

✧ In an e-commerce system, the application-specific layer includes additional functionality

supporting a ‘shopping cart’ in which users can place a number of items in separate
transactions, then pay for them all together in a single transaction.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Server implementation
✧ These systems are often implemented as multi-tier client server/architectures (discussed in
Chapter 17)
○ The web server is responsible for all user communications, with the user interface implemented using a web
browser;

○ The application server is responsible for implementing application-specific logic as well as information storage
and retrieval requests;

○ The database server moves information to and from the database and handles transaction management.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Language processing systems
✧ Accept a natural or artificial language as input and generate some other
representation of that language.
✧ May include an interpreter to act on the instructions in the language that
is being processed.
✧ Used in situations where the easiest way to solve a problem is to
describe an algorithm or describe the system data
○ Meta-case tools process tool descriptions, method rules, etc and generate
tools.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
The architecture of a language processing system

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Compiler components
✧ A lexical analyzer, which takes input language tokens and converts them to an internal form.

✧ A symbol table, which holds information about the names of entities (variables, class names,
object names, etc.) used in the text that is being translated.

✧ A syntax analyzer, which checks the syntax of the language being translated.

✧ A syntax tree, which is an internal structure representing the program being compiled.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Compiler components
✧ A semantic analyzer that uses information from the syntax tree and the symbol table to
check the semantic correctness of the input language text.

✧ A code generator that ‘walks’ the syntax tree and generates abstract machine code.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
A repository architecture for a language processing system

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
A pipe and filter compiler architecture

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Key points
✧ A software architecture is a description of how a software system is organized.

✧ Architectural design decisions include decisions on the type of application, the distribution
of the system, the architectural styles to be used.

✧ Architectures may be documented from several different perspectives or views such as a

conceptual view, a logical view, a process view, and a development view.

✧ Architectural patterns are a means of reusing knowledge about generic system architectures.
They describe the architecture, explain when it may be used and describe its advantages and
disadvantages.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Key points
✧ Models of application systems architectures help us understand and compare applications,
validate application system designs and assess large-scale components for reuse.

✧ Transaction processing systems are interactive systems that allow information in a database
to be remotely accessed and modified by a number of users.

✧ Language processing systems are used to translate texts from one language into another and
to carry out the instructions specified in the input language. They include a translator and an
abstract machine that executes the generated language.

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025
Questions?!

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025 60
 Stay in touch!

ha.eldeeb@gmail.com
@hassaneldeeb
@_HassanEldeeb_

Dr. Hassan Eldeeb Software Engineering: Architectural Design Software Engineering- Mar, 2025 61