Application architectures - Software Architecture and Design

Chapter 1 – Architectural Design
Mutah University
Faculty of IT
Department of Software Engineering
Dr. Ra’Fat A. AL-Msie’Deen
rafatalmsiedeen@mutah.edu.jo
https://rafat66.github.io/Al-Msie-Deen/
Software Architecture and Design

Reference - Text Book:
 Chapter 6 of Software Engineering book - by Ian
Sommerville. l0th Edition. Addison Wesley, 2015, ISBN-
10: 0137035152.
2

Topics covered
 Architectural design decisions
 Architectural views
 Architectural patterns
 Application architectures
318/03/2020

Application architectures
 Application systems are intended to meet a business or
an organizational need.
 All businesses have much in common—they need to hire
people, issue invoices, keep accounts, and so on.
 Businesses operating in the same sector use common
sector specific applications.
 Therefore, as well as general business functions, all
phone companies need systems to connect and meter
calls, manage their network and issue bills to customers.
 Consequently, the application systems used by these
businesses also have much in common.
5

Application architectures … cont.
 These commonalities have led to the development of
software architectures that describe the structure and
organization of particular types of software systems.
 Application architectures encapsulate the principal
characteristics of a class of systems.
 For example, in real-time systems, there might be
generic architectural models of different system types,
such as data collection systems or monitoring systems.
 Although instances of these systems differ in detail, the
common architectural structure can be reused when
developing new systems of the same type.
6

 The application architecture may be reimplemented when
developing new systems.
 However, for many business systems, application
architecture reuse is implicit when generic application
systems are configured to create a new application.
 We see this in the widespread use of Enterprise Resource
Planning (ERP) systems and off-the-shelf configurable
application systems, such as systems for accounting and
stock control.
 These systems have a standard architecture and
components.
 The components are configured and adapted to create a
specific business application. 7

 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.
 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.
818/03/2020

Use of application architectures
 For example, a system for supply chain management
can be adapted for different types of suppliers, goods,
and contractual arrangements.
 As a software designer, you can use models of
application architectures in a number of ways:
1. As a starting point for the architectural design
process
 If you are unfamiliar with the type of application that
you are developing, you can base your initial design
on a generic application architecture.
 You then specialize this for the specific system that is
being developed. 9

Use of application architectures … cont.
2. As a design checklist
 If you have developed an architectural design for an
application system, you can compare this with the
generic application architecture.
 You can check that your design is consistent with the
generic architecture.
10

3. As a way of organizing the work of the development
team
 The application architectures identify stable structural
features of the system architectures, and in many
cases, it is possible to develop these in parallel.
 You can assign work to group members to implement
different components within the architecture.
11

4. As a means of assessing components for reuse
 If you have components you might be able to reuse,
you can compare these with the generic structures to
see whether there are comparable components in the
application architecture.
12

5. As a vocabulary for talking about applications
 If you are discussing a specific application or trying to
compare applications, then you can use the concepts
identified in the generic architecture to talk about
these applications.
13

1) As a starting point for architectural design.
2) As a design checklist.
3) As a way of organizing the work of the development
team.
4) As a means of assessing components for reuse.
5) As a vocabulary for talking about application types.
14

 There are many types of application system, and, in
some cases, they may seem to be very different.
 However, superficially dissimilar applications may have
much in common and thus share an abstract application
architecture.
 I illustrate this by describing the architectures of two
types of application:
15

Examples of application types
1. Transaction processing applications
 Transaction processing applications are database-
centered applications that process user requests for
information and update the information in a database.
 These are the most common types of interactive
business systems.
 They are organized in such a way that user actions can’t
interfere with each other and the integrity of the
database is maintained.
 This class of system includes interactive banking
systems, e-commerce systems, information systems,
and booking systems. 16

Examples of application types … cont.
2. Language processing systems
 Language processing systems are systems in which the
user’s intentions are expressed in a formal language, such
as a programming language.
 The language processing system processes this language
into an internal format and then interprets this internal
representation.
 The best known language processing systems are
compilers, which translate high-level language programs
into machine code.
 However, language processing systems are also used to
interpret command languages for databases and
information systems, and markup languages such as XML.

 I have chosen these particular types of system because
a large number of web based business systems are
transaction processing systems, and all software
development relies on language processing systems.
18/03/2020 18

 Data processing applications
 Data driven applications that process data in batches
without explicit user intervention during the processing.
 Transaction processing applications
 Data-centered 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. 19

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.
20

Key points
 Models of application systems architectures help us
understand and compare applications, validate
application system designs and assess large-scale
components for reuse.
21

Transaction processing systems

 Transaction processing systems are designed to process
user requests for information from a database, or
requests to update a database (Lewis, Bernstein, and
Kifer 2003).
 Technically, a database transaction is part of a sequence
of operations and is treated as a single unit (an atomic
unit).
 All of the operations in a transaction have to be
completed before the database changes are made
permanent.
 This ensures that failure of operations within a
transaction does not lead to inconsistencies in the
database.
23

Transaction processing systems … cont.
 From a user perspective, a transaction is any coherent
sequence of operations that satisfies a goal, such as
“find the times of flights from London to Paris.”
 If the user transaction does not require the database to
be changed, then it may not be necessary to package
this as a technical database transaction.
18/03/2020 24

 An example of a database transaction is a customer
request to withdraw money from a bank account using
an ATM.
 This involves checking the customer account balance to
see if sufficient funds are available, modifying the
balance by the amount withdrawn and sending
commands to the ATM to deliver the cash.
 Until all of these steps have been completed, the
transaction is incomplete and the customer accounts
database is not changed.
25

 Transaction processing systems are usually interactive systems
in which users make asynchronous requests for service.
 Figure 1 illustrates the conceptual architectural structure of
transaction processing applications.
 First, a user makes a request to the system through an I/O
processing component.
 The request is processed by some application-specific logic.
 A transaction is created and passed to a transaction manager,
which is usually embedded in the database management
system.
 After the transaction manager has ensured that the transaction
is properly completed, it signals to the application that
processing has finished. 26

 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.
27

The structure of transaction processing applications
28
Figure 1. The structure of transaction processing applications.

 Transaction processing systems may be organized as a “pipe
and filter” architecture, with system components responsible
for input, processing, and output.
 For example, consider a banking system that allows customers
to query their accounts and withdraw cash from an ATM.
 The system is composed of two cooperating software
components — the ATM software and the account processing
software in the bank’s database server.
 The input and output components are implemented as
software in the ATM, and the processing component is part of
the bank’s database server.
 Figure 2 shows the architecture of this system, illustrating the
functions of the input, process, and output components. 29

The software architecture of an ATM system
30
Figure 2. The software architecture of an ATM system.

Key points
 Transaction processing systems are interactive systems
that allow information in a database to be remotely
accessed and modified by a number of users.
31

Information systems

Information systems
 All systems that involve interaction with a shared
database can be considered to be transaction-based
information systems.
 An information system allows controlled access to a
large base of information, such as a library catalog, a
flight timetable, or the records of patients in a hospital.
 Information systems are almost always web-based
systems, where the user interface is implemented in a
web browser.
33

Information systems … cont.
 Figure 1 presents a very general model of an information
system.
 The system is modeled using a layered approach
(discussed in Section 6.3) where the top layer supports
the user interface and the bottom layer is the system
database.
 The user communications layer handles all input and
output from the user interface, and the information
retrieval layer includes application-specific logic for
accessing and updating the database.
 The layers in this model can map directly onto servers in
a distributed Internet-based system.
34

Layered information system architecture
35Figure 1. Layered information system architecture.

Information systems architecture
 Information systems have a generic architecture that can
be organized 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
36

The architecture of the Mentcare system
 As an example of an instantiation of this layered model,
Figure 2 shows the architecture of the Mentcare system.
 Recall that this system maintains and manages details of
patients who are consulting specialist doctors about
mental health problems.
 I have added detail to each layer in the model by
identifying the components that support user
communications and information retrieval and access.
18/03/2020 37

The architecture of the Mentcare system … cont.
38
Figure 2. The architecture of the Mentcare system.

1) The top layer is a browser-based user interface.
2) The second layer provides the user interface
functionality that is delivered through the web browser.
It includes components to allow users to log in to the
system and checking components that ensure that the
operations they use are allowed by their role. This layer
includes form and menu management components that
present information to users, and data validation
components that check information consistency.
39

3) The third layer implements the functionality of the
system and provides components that implement
system security, patient information creation and
updating, import and export of patient data from other
databases, and report generators that create
management reports.
4) Finally, the lowest layer, which is built using a
commercial database management system, provides
transaction management and persistent data storage.
40

Web-based information systems
 Information and resource management systems are
sometimes also transaction processing systems.
 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.
41

Web-based information systems … cont.
 The organization of servers in these systems usually
reflects the four-layer generic model presented in Figure
1.
 These systems are often implemented as distributed
systems with a multitier client server/architecture.
42

Layered information system architecture
43
Figure 1. Layered information system architecture.

1. The web server is responsible for all user
communications, with the user interface implemented
using a web browser;
2. The application server is responsible for implementing
application-specific logic as well as information storage
and retrieval requests;
3. The database server moves information to and from
the database and handles transaction management.
18/03/2020 44

 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.
45

Server implementation
 These systems are often implemented as multi-tier client
server/architectures.
 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.
46

Server implementation … cont.
 Using multiple servers allows high throughput and
makes it possible to handle thousands of transactions
per minute.
 As demand increases, servers can be added at each
level to cope with the extra processing involved.
47

Key points
 All systems that involve interaction with a shared
database can be considered to be transaction-based
information systems.
 An information system allows controlled access to a
large base of information, such as a library catalog.
 Information systems are almost always web-based
systems, where the user interface is implemented in a
web browser.
48

Application architectures - Software Architecture and Design

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