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Advanced Software EngineeringURL: http://lore.com/Advanced-Software-Engineering-Univaq/

DISIMDep.nt of Information Engineering, Computer Science and MathematicsUniversity of L’Aquila, Italy

Software Architecture

Henry Muccini henry.muccini@univaq.it, @muccinihenry, henrymuccini.com

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Copyright Notice

The material in these slides may be freely reproduced and distributed, partially or totally, as far as an explicit reference or acknowledge to the material author is preserved.

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Software ArchitectureThe Software Architecture is the earliest model of the whole software system created along the software lifecycle

“Traditional” definition:→A set of components and connectors communicating through interfaces

“More Recent” understanding“Other facets”

→A set of architecture design decisions taken to generate the architecture artifact

→Focus on set of Views and Viewpoints, looking at stakeholders and their concern

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«Traditional» definitions

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Software Architecture definitionsPerry and Wolf, ’92 (aspects):

→“Architecture is concerned with the selection of architectural elements, their interactions, and the constraints on those elements and their interactions necessary to provide a framework in which to satisfy the requirements and serve as a basis for the design.”

→Elements are divided into processing elements, data elements and connection elements

Garlan and Shaw, ’93 (elements):→ Architecture for a specific system may be captured as “a collection of computational components - or simply components - together with a description of the interactions between these components - the connectors -”

Sommerville, 7th edition, ’04 (process):→ The design process for identifying the sub-systems making up a system and the framework for sub-system control and communication is architectural design. The output of this design process is a description of the SA.

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In general terms…SA describes (in a more or less “formal” notation) how a system is structured into components and connectors…

→Components→Connectors→Channels and Ports

… and how these components interact→ Scenarios→State Diagrams→…

SA Structure (topology)

SA Dynamics (behavior)

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Process (1)

Software SystemSoftware Architecture

Architecturalcomponents

CompositionRules

Constraints

RequirementsIdeal World Real World

Software SystemSoftware Architecture

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Process (2)

Architectural constraints and requirements

Ideas

Constraints

Req1:..Req2:..Req3:..………

Architectural requirements

C2

C3C1

C4

Software Architecture

Software Architecture

synthesis

C2

C3C1

C4Software Architecture

prototypeEvaluation and Decisions making

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STATIC DESCRIPTION

ComponentsConnectorsInterfaces

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Components

A component is a building block that is …→A unit of computation or a data store, with an interface specifying the services it provides and requires→A unit of deployment→A unit of reuse

─ e.g., client, server, database, filters, ...

C1

S1S2S3

S’x

S’Y

provided services

required services

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Component: ExampleSupply manager:

This module task is to automatically satisfy the request of supplies by the TLs,

it forwards the request of supplies to the military warehouse in order to automatically set up the shipping of supplies for whose that requested it.

It will not always send all the supplies requested since it depends on the warehouse resources availability and, more important, on the rules that has been set by the HQ user.

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Components vs Objects

The level of abstraction is usually different

Size→Objects tend to be small→Components can be small (one object) or large (a library of objects or a complete application)

An architectural component may be implemented by several objects

Lifecycle →Objects are created and destroyed constantly→Components are created and destroyed infrequently

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ConnectorsA connector is a building block that enables interaction among components

→Events→Client/server middleware→Messages and message buses→Shared variables→Procedure calls (local or remote)→Pipes

Connectors may be implicit or explicit→Connectors sometimes are just channels→Connectors sometimes have their own logic and complexity

Connectors may be endogenous or exogenous

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Components and ConnectorsA component is (or should be) independent of the context in which it is used to provide services

A connector is (or should be) dependent on the context in which it is used to connect components

Connectors sometimes are modeled as special kinds of components

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InterfacesAn interface is the external connection of a

component (or connector) that describes how to interact with it

Provided and required interfaces are importantSpectrum of interface specification

→ Loosely specified (events go in, events go out)→ API style (list of functions)→ Very highly specified (event protocols across the interface

in CSP)

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Architecting: example

GUI

FeedServiceFeedServiceCommon

Action

NewsFeederAction

AdminAction

Factory

FeedDelegatePOJOs

NewsFeederDAO

FeedDAO

NewsFeederDAO

FeedDAO

FeedDelegate

TransferObject

ValidatorService

NewsFeederDelegatePOJOs

NewsFeederDelegate

Browser(html

javascript)

WebServices

DATABASE

TrasformationValidation

BusinessFactory

ValidationService

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Architecting: example

GUI

FeedServiceFeedService

CommonAction

NewsFeederAction

AdminAction

Factory

FeedDelegatePOJOs

NewsFeederDAO

FeedDAO

NewsFeederDAO FeedDAO

FeedDelegate

Transfer Object

ValidatorService

NewsFeederDelegatePOJOs

NewsFeederDelegate

Browser(html

javascript)

Web Services

DATABASE

TrasformationValidation

BusinessFactory

ValidationService

BusinessExtensionIn

BusinessExtensionOut

PresentationExtensionOut

PresentationExtensionIn

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Architectural Elements vs Design Elements

“Architecture is concerned with the selection of architectural elements, their interactions, and the constraints on those elements and their interactions necessary to provide a framework in which to satisfy the requirements and serve as a basis for the design.”

“Design is concerned with the modularization and detailed interfaces of the design elements, their algorithms and procedures, and the data types needed to support the architecture and to satisfy the requirements.”

(Perry & Wolf 92)

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Architectural Elements vs Design Elements“The architecture of a software system defines that

system in terms of computational components and interactions among those components. … In addition to specifying the structure and topology of the system, the architecture shows the correspondence between the requirements and elements of the constructed system, thereby providing some rationale for the design decisions.”

(Shaw & Garlan 96)

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DYNAMIC DESCRIPTION

Behavioral models

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SA dynamics

The SA dynamics is expressed in terms of component interactions via connectors

• Labeled Transition Systems • Automata• UML StateCharts, Sequence Diagrams, Activity Diagrams• State Diagrams• Message Sequence Charts• …

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Customer Interface

Customer Process

Web Server

Customer Server

Order Server

Cart Server

Catalog ServerDelivery Order

Process

SA Static Description

AN EXAMPLE : E-COMMERCE SYSTEM

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SA Dynamic Description : Browse Catalogue Sequence Diagram

CustomerInterface

Registered Customer

CustomerProcess CatalogServer

Catalog DBInvolved

BrowseCatalog

BrowseCatalog

ReadStatus

Catalog Page

Output Page

Catalog Info

AN EXAMPLE : E-COMMERCE SYSTEM

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CustomerInterface

Registered Customer

CustomerProcess CartServer

PlaceOrderReq

PlaceOrder

ReadStatus

Cart DBInvolved

pageOrderOutputPage

Order DBInvolved

OrderServer

EmptyCart

Cart DBInvolved

CustomerServer

ReadInfo

CustomerDB Involved

DeliveryOrderProcess

createNewOrder

OrderInfo

newOrder

CartInfo

CustomerInfo

OrderInfo

SA Dynamic Description : Place Order Sequence Diagram (success)

AN EXAMPLE : E-COMMERCE SYSTEM

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SA Dynamic Description : Place Order Sequence Diagram (empty cart)

CustomerInterface

Registered Customer

CustomerProcess CartServer

PlaceOrderReq

PlaceOrder

ReadStatus

Cart DBInvolved

errorPageOutputPage

emptyCart

AN EXAMPLE : E-COMMERCE SYSTEM

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MORE RECENT UNDERSTANDING

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Architecture Is a Set of Software Structures

“The software architecture of a system is the set of structures needed to reason about the system, which comprise software elements, relations among them, and properties of both.” [SAinPractice_book]

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Architecture Is a Set of Software Structures

Three categories of structures:

1. Structure = implementation units = modules

2. Dynamic structures

3. mapping from software structures to the system’s organizational, developmental, installation, and execution environments.

implications

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EXAMPLE (FOR DISCUSSION)

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Application Example: Voting System

“We want to build a software system that allows people to vote electronically.

→ The citizen goes to the electoral place, and she votes using a hw/sw device.

→ The vote is stored locally and automatically sent to other computers.

→ The citizen identity must be validated by the system→ …”

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Basic Requirement Example

The voting system must satisfy the following requirements:

→ One voter – one vote (no more than one vote for voter)→ The voter can vote in only one previous designated voting

place→ The voter must be identified by the election officials at the

voting place─ The citizen identity must be validated by the system

→ It is not possible to trace the votes back to the voters→ The election officials can’t read the results, guarantying that

the results are unknown until the end of the voting process

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Example

Terminal

Activate