SE2_Lec 17_ Architectural Design

1َدرِنقْْنصدق اننالما،،، ِنـْقـَدر

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The software architecture of a program or computing

system is the structure (or structures) of the system,

including:

Dividing software into subsystems.

Deciding how these will interact.

Determining their interfaces.

• The architecture is the core of the design, so all software

engineers need to understand it.

• The architecture will often constrain the overall efficiency,

reusability and maintainability of the system

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Why you need to develop an architectural model:

To enable everyone to better understand the system

To allow people to work on individual pieces of the system

in isolation

To prepare for extension of the system

To facilitate reuse and reusability

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An architecture is an abstraction of a system that

suppresses details of components that do not affect how

they:

Use other components

Are used by other components

Relate to other components

Interact with other components

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To ensure the maintainability and reliability of a system,

an architectural model must be designed to be stable.

Being stable means that the new features can be easily

added with only small changes to the architecture.

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aTruck aShip aAirplane theWarehouseCollecti on

theVehicleCollection

UML-A Generated Dependency Class:theRouter Dependency (1.0)

theStorage

aVehicle


availableVehicleCollection

UML-A Generated Association Class:theVehicleCollection Generalization (1.0)UML-A Generated Association Class:theVehicleCollection Generalization (1.0)UML-A Generated Association Class:theVehicleCollection Generalization (1.0)UML-A Genera ted As socia tion C lass: theVehicleC ollec tion Genera lization (1.0)UML-A Generated Association Class:theVehicleCollection Generalization (1.0)UML-A Generated Association Class:theVehicleCollection Generalization (1.0)UML-A Generated Association Class:theVehicleCollection Generalization (1.0)UML-A Generated Association Class:theVehicleCollection Generalization (1.0)UML- A Generated Ass ociati on Cl ass:theVehi cleCo llection Generali zation (1.0 )UML-A Generated Association Class:theVehicleCollection Generalization (1.0)


availableGoods

aPort

aPortC ollec tion

aSurp lus aDifficiency

theTimeNeeded

theGoods

UML-A Generated Association Class:aWarehouse Association (0.5)


UML-A Generated Association Class:availableGoods Association (0.5)

aRouteCollection

UML-A Generated Association Class:aRoute Association (0.25)UML-A Generated Association Class:aRoute Association (0.25)UML-A Generated Association Class:aRoute Association (0.25)UML-A Generated Association Class:aRoute Association (0.25)

UML-A Generated Dependency Class:theRouter Dependency (0.5)UML-A Generated Dependency Class:theRouter Dependency (1.0)


theAWT

aVehiceDialog aWarehouseDialog aPortDialog aRouterDialog

aWarehouse

UML-A Generated Association Class:aDifficiency Association (1.0)UML-A Generated Association Class:aDifficiency Association (1.0)

UML-A Generated Association Class:aDifficiency Association (1.0)UML-A Generated Association Class:aDifficiency Association (1.0)

UML-A Generated Association Class:aDifficiency Association (1.0)U ML-A Generated Association Class:aD ifficiency Associ ation (1.0)UML-A Generated Association Class:aDifficiency Association (1.0)UML-A Generated Association Class:aDifficiency Association (1.0)U ML-A Generated Association Class:aD ifficiency Associ ation (1.0)UML-A Generated Association Class:aDifficiency Association (1.0)

UML-A Genera ted Associ ation C lass:aSurp lus Associ ation (1.0)UML-A Generated Association Class:aSurplus Association (0.5)

UML-A Generated Associ ation Class:aRoute Association (0.5)

aLocation

UML-A Generated Association Class:aNavPoint Association (1.0)



UML-A Generated Association Class:aNavPoint Association (0.5)UML-A Generated Association Class:aNavPoint Association (0.5)

UML-A Generated Association Class:aWarehouse Association (0.5)aNavPoint


UML-A Generated Association Class:aWarehouse Association (0.5)UML-A Generated Association Class:aWarehouse Association (0.5)



UML-A Generated Association Class:aRoute Association (0.5)

aRoute

UML-A Genera ted Dependency C lass :aRouteCol lection Ass ociation (0.25)



UML-A Generated Dependency Class:aRouteCollection Association (0.5)

UML-A Generated Association Class:aNavPoint Association (1.0)UML-A Generated Association Class:aNavPoint Association (1.0)UML-A Generated Association Class:aNavPoint Association (1.0)UML-A Generated Association Class:aNavPoint Association (1.0)UML-A Generated Association Class:aNavPoint Association (1.0)



UML-A Generated Dependency Class:theRouter Association (0.25)


theCargoRouter

UML-A Generated Association Class:theRouter Association (0.25)

UML-A Genera ted As socia tion C lass: theWarehouseCollection Dependency ( 0.25)



t heRouter

UML-A Generated Association Class:theWarehouseCollection Dependency (0.5)

UML-A Generated Association Class:theWarehouseCollection Dependency (0.5)

UML-A Genera ted Dependency Class :aRouteCollection Ass ociation (0.5)UML-A Generated Association Clas s:theWarehouseCollec tion Dependency (0.5)

UML-A Generated Association Class:theVehicleCollection Dependency (0.5)UML-A Generated Association Class:availableVehicleCollection Dependency (0.5)UML- A Generated Generaliz ation Class :avail ableVehicleCollection Dependenc y (1.0 )


UML-A Generated Dependency Class:theRouter Association (0.5)UML-A Generated Dependency Class:theRouter Association (1.0)


UML-A Generated Dependency Class:theWarehouseCollection Dependency (1.0)

UML-A Generated Dependency Class:theRouter Association (1.0)UML-A Generated Dependency Class:theRouter Association (1.0)

This is a simplesoftware system!

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Independent Components

Communicating

Processes

Event Systems

Client/Server Peer-to-PeerImplicit

Invocation

Explicit

Invocation

Data Flow

Batch Sequential Pipe & Filter

Virtual Machine

Interpreter Rule-Based

System

Data-Centered

Repository Blackboard

Call and Return

Main Program

and Subroutine

Object

OrientedLayered

Remote Procedure Call

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Shared Data

Client A Client B Client C

Client D Client E Client F

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Has goal of achieving the quality of integrability of data.

The term refers to systems in which the access and update

of a widely accessed data store is their primary goal.

Basically, it is nothing more than a centralized data store

that communicates with a number of clients.

Important for this styles are three protocols:

communication, data definition and data manipulation

protocol

A client runs on an independent thread of control.

The means of communication distinguishes the two

subtypes: repository and blackboard

Repository: a client sends a request to the system to performa necessary action (e.g. insert data)

Blackboard: the system sends notification and data tosubscribers when data of interest changes, and is thus active

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Ensures data integrity

Reliable, secure, easy to Backup, testability guaranteed

Clients independent on the system: performance and

usability on the client side is good

Problems with scalability

Solutions: shared repositories, replication but this

increases complexity

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One of the most well-known examples of the data-centered architecture, is a database architecture

E.g. in RDBMS a set of related tables with fields, datatypes, keys, ...

Clients use data manipulation protocol to work with thedata

E.g. SQL for inserting, selecting, deleting data, ...

Depending on where clients are situated communicationprotocol might be

An inner-process communication

Communication between components on the same machine

Communication over network, e.g. LAN, Internet, etc.

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Has the goal of achieving the quality of reuse and

modifiability.

The data-flow style is characterized by viewing the system

as a series of transformations on successive pieces of input

data.

Data enter the system and then flows through the

components one at a time until

Finally, the data is assigned to some final destination

(output or a data store).

The architecture is very flexible.

Almost all the components could be removed.

Components could be replaced.

New components could be inserted.

Certain components could be reordered.

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Validate Sort Update Report

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Batch sequential style

The processing steps are independent components

Each step runs to completion before the next step begins

Pipe-and-filter style

Emphasizes the incremental transformation of data by

successive components

The filters incrementally transform the data (entering and

exiting via streams)

The pipes are stateless and simply exist to move data

between filters

Note That: It is easily made into a parallel or distributedexecution in order to enhance system performance

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Data flows through pipes: communication channels

between filters

Processing units: filters

Filters do not know anything about other filters

Modularity, maintainability is good

Data flows in streams: good for processing of images,

audio, video, ...

Depending on where the filters reside different

execution architectures

E.g. same process: filters run within threads

E.g. same machine: filters run within own processes

E.g. network: pipes use the networking architecture

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Pipe and Filter Example:

Traditional Compilers: Compilation phases are pipelined,

though the phases are not always incremental. The phases

in the pipeline include

• lexical analysis + parsing + semantic analysis + code

generation

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Main module

Subroutine ASubroutine B

Subroutine A-1 Subroutine A-2

Physical layer

Data layer

Network layer

Transport layer

Application layer Class WClass V

Class X

Class Z

Class Y

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Has the goal of modifiability and scalability

Has been the dominant architecture since the start of

software development

Main program and subroutine style

Decomposes a program hierarchically into small pieces (i.e.,

modules)

Typically has a single thread of control that travels through

various components in the hierarchy

Remote procedure call style

Consists of main program and subroutine style of system that is

decomposed into parts that are resident on computers

connected via a network

Strives to increase performance by distributing the computations

and taking advantage of multiple processors

Incurs a finite communication time between subroutine call and

response.

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Object-oriented or abstract data type system

Emphasizes the bundling of data and how to manipulate and

access data

Keeps the internal data representation hidden and allows access

to the object only through provided operations

Permits inheritance and polymorphism

Layered system

Assigns components to layers in order to control inter-

component interaction

Only allows a layer to communicate with its immediate neighbor

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Layering: the structure of the system is organized into

set of layers

Each layer in on the top of another layer, each layer

communicates only with the layer immediately below it.

The higher layer sees the lower layer as a set of services.

Well-defined interfaces between layers

Reduces complexity,

improves modularity,

reusability,

maintainability

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Typically organized into layers

Successive layers provide more sophisticated services to

the layers above them

Hardware services, kernel services, system services, UI

services

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A virtual machine implements an

instruction set for an imaginary

machine

Often virtual machines are the

underplaying mechanism by which

a programming language is

executed

E.g. Java virtual machine, different

interpreters

• Specifies an interface between

compiler and a real machine

From conceptual point of view very

similar to OS

Improves portability

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A common example of layered architecture is a network

protocol stack

E.g. TCP/IP protocol stack - Four layers

The lowest layer: handles communication between two

computers

The internet layer: handles routing of packets across the

network

The transport layer: guarantees that packets are error-

free and received in the same order as sent

The application layer: supports application-specific

protocols

• E.g. HTTP, SMTP, FTP, ...

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Basic concept:

The client uses a service

The server provides a service

Typically connected via a network

Clients are independent from each other

There is at least one component that has the role of

client, initiating connections in order to obtain some

service.

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Conceptually simple

Clear separation of responsibilities, help testability

Good scalability (if stateless)

Excellent scalability (if server can be scaled out)

Good for security, as data can be held at the server with

restricted access

Risk of bad performance, if the communication between

client and server is slow, or has a high latency

Need to develop/agree on a protocol between client and

server

For stateful, centralized servers scalability is limited

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The server is no longer in the organizations network, but

somewhere in the Internet

Example: cloud services by Salesforce, Google,

Microsoft

Scalability, security, reliability is expected to be

handled by a specialized team

Needs a working Internet connection

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Separation between client and server is removed

Each client is a server at the same time, called peer

The goal is to distribute the processing or data among many

peers

No central administration or coordination

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Example: Skype uses a peer-to-peer protocol, but also

uses super-nodes and a central login servers

Adv.

Good for scalability

Good for reliability, as data can be replicated over peer

No single point of failure

Disadv.

Quality of service is not deterministic, cannot be guaranteed

Very complex, hard to maintain and test

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The N-tier architecture is the modern client-server

architecture

Originated with business applications

Through the popularity of the Web today typically

related with Web applications

Conceptually separate architecture into:

Presentation,

Application, and

Data storage layers.

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Clients are typically rich

(ui + app-logic + communication)

Servers store data

Each client runs a complete application

Drawbacks: each client has to know how to

communicate with all data servers

Scalability is compromised because client are tightly

coupled with servers

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Evolved from 2-tier architectures to solve

their drawbacks

A third tier is inserted between clients

and data servers

Application or business logic tier: middle

tier.

Typically middle tier is on the server side

(but recently might be split between the

server and the client)

Scalability improved because clients are

thinner.

Thin clients have no knowledge on

application

A rich client contains full knowledge of

application

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Suitable for applications in which a central issue is

identifying and protecting related bodies of data.

Data representations and their associated operations are

encapsulated in an abstract data type.

Components: are objects.

Connectors: are function and procedure invocations

(methods).

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Object-Oriented Invariants

The data representation is hidden from other objects.

Advantages

it is possible to change the implementation without

affecting those clients.

Can design systems as collections of autonomous

interacting agents.

Disadvantages

In order for one object to interact with another object (via

a method invocation) the first object must know the

identity of the second object

Objects cause side effect problems:

• E.g., A and B both use object C, then B’s effects on C look

like unexpected side effects to A.

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Suitable for applications that involve loosely-coupled

collection of components, each of which carries out

some operation and may in the process enable other

operations.

Instead of invoking a procedure directly ...

A component can announce (or broadcast) one or more

events.

Other components in the system can register an interest in

an event by associating a procedure with the event.

When an event is announced, the broadcasting system

(connector) itself invokes all of the procedures that have

been registered for the event.

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Advantages:

Provides strong support for reuse.

Eases system evolution

Disadvantages:

When a component announces an event:

• it has no idea what other components will respond to it,

• it cannot rely on the order in which the responses are

invoked

• it cannot know when responses are finished

Twitter, Google+

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Remote invocation architectures involve distributed

processing components

Typically, a client component invokes a method

(function) on a remote component

E.g. Web services

Advantages:

increased performance through distributed computation

Disadvantages:

tightly coupling of components

increases communication overhead

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Transparently distribute

aspects of the software

system to different nodes

An object can call

methods of another

object without knowing

that this object is

remotely located.

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Systems are seldom built from a single architectural

style

Three kinds of heterogeneity:

Locationally heterogeneous

• The drawing of the architecture reveals different styles in

different areas (e.g., a branch of a call-and-return system

may have a shared repository)

Hierarchically heterogeneous

• A component of one style, when decomposed, is structured

according to the rules of a different style

Simultaneously heterogeneous

• Two or more architectural styles may both be appropriate

descriptions for the style used by a computer-based system

42َدرِنقْْنصدق اننالما،،، ِنـْقـَدر

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Are concerned with the control flow between sub-

systems.

Centralized control

One sub-system has overall responsibility for control and

starts and stops other sub-systems

Event-based control

Each sub-system can respond to externally generated

events from other sub-systems or the system’s

environment

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A control sub-system takes responsibility for managing

the execution of other sub-systems

Call-return model

Top-down subroutine model

Control starts at the top of a subroutine hierarchy and

moves downwards.

Applicable to sequential systems

Manager model

One system component controls the stopping, starting

and coordination of other system processes.

Applicable to concurrent systems.

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Routine 1.2Routine 1.1 Routine 3.2Routine 3.1

Routine 2 Routine 3Routine 1

Mainprogram

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Systemcontroller

Userinterface

Faulthandler

Computationprocesses

Actuatorprocesses

Sensorprocesses

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Driven by externally generated events where the

timing of the event is outside the control of the sub-

systems which process the event

Two principal event-driven models:

Broadcast models. An event is broadcast to all sub-

systems. Any sub-system which can handle the event

may do so

Interrupt-driven models. Used in real-time systems

where interrupts are detected by an interrupt handler

and passed to some other component for processing

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Sub-system1

Event and message handler

Sub-system2

Sub-system3

Sub-system4

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Handler1

Handler2

Handler3

Handler4

Process1

Process2

Process3

Process4

Interrupts

Interruptvector

SE2_Lec 17_ Architectural Design

Software

Transcript of SE2_Lec 17_ Architectural Design