Università degli Studi dell’Aquila

L06: Design Decisions

Henry Muccini

DISIM Department, University of L’Aquila

henry.muccini@univaq.it

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.

Some of the slides have been originally made by prof.

Patricia Lago.Patricia Lago.

Thanks to Smrithi for the discussion we had on the topic

Henry Muccini

Intro to Software Testing

Structural Testing

Model-based Testing

Architecture-based Testing

Lab

Intro to SA

SA Case study

SA style

ADLs

Design Decisions

Views/Viewpoints

Non Functional S.E.

Performance modeling

Performance analysis

UML

UML Profiling

Lab

Views/Viewpoints

Software Architecture

The 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 →A set of components and connectors communicating through interfaces

“Recent/Future” understanding:

→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

Architecting today

Architecting is the process of creating software

architecture knowledge and artifacts for engineering

software systems

A Software Architecture consists of

→A blueprint for the chosen solution (product)

→A set of design decisions (co-product)

Architecture as a set of Design Architecture as a set of Design

Decisions

Design Rationale and Design Decision

Design is a problem-solving process whose objective is to find and describe a way:

�To implement the functional requirements...�while respecting the non-functional requirements �and yet deliver 'good' quality

The result of software Design:

�A blueprint for the chosen solution (product)

�A set of design decisions (co-product)

A designer is faced with a series of design issues

�These are sub-problems of the overall design problem.

�Each issue normally has several alternative solutions (or

design options)

�The designer makes a design decision to resolve each issue.�The designer makes a design decision to resolve each issue.

This process involves choosing the best option

from among the alternatives.

Taking decisionsDesignproblem

sub-problem(or issue)

sub-problem (or issue)

Problem space

Designoption

Designoption

Designoption

Designoption

Solution space

Alternativesolutions

Alternativesolutions

Decision =best option

Decision =best option

Best, with respect to

some criterion

Design space

The space of possible designs that could be achieved

by choosing different sets of alternatives.

web browserbased

fat-client

architecture

client-server

peer clients

thin-client

rich-client

based

custom clientprogram

clientstyle

layered

peer-to-peer

architecturestyle

structured p2p

unstructured p2p

hybrid p2p

tiered

...

Taking decisions /2

To take each design decision, the software engineer

uses:

→“current” knowledge

─ the requirements

─ the design as created so far

→and “past” knowledge

─ the technology available

─ what has worked well in the past

─ software design principles and “best practices”

�Collection of Requirements and Constraints

�Identification of Design Issues

�Identification of Design Alternatives

�Identification of Design Decisions (DDs)�Identification of Design Decisions (DDs)

�Selection of architectural Components

�Selection of an architectural Solutions that comply to

the DDs

Design Issue 1: how many gateways shall be used to collect sensored data in a building?

Design Issue2: how to propagate the collected data to the fire station?

Design Issue 3: how the sensors are connected?

Design Issue 4: how the sensors should be powered?

Design Issue 5: how to sense how many people are present in the building?

…

DI1: how many

Single

Gateway Cost

Design Issue

Design

alternativesCriteria

DI1: how many

gateways shall be

used to collect

sensored data in a

building?

1 gateway per

floor

1 Gateway per

apartment

Reliability

Availability

DD1: one gateway per floor

DD2: WAN

DD3: Wireless Lan

DD4: batteryDD4: battery

DD5: counting

sensors

…

DD1: only one gateway

DD2: WAN

DD3: LAN

DD4: batteryDD4: battery

DD5: counting

sensors

…

Why DD?

According to Anton Jansen and Jan Bosch [4], defining

Architecture as a set of design decisions helps the

architect to:

a. Guard the conceptual Integrity of the Software architecture

b. Communicate effectively the design space explorationb. Communicate effectively the design space exploration

c. Effectively analyze the software architecture and design

process

d. Trace design decisions and their relationship to the

resulting architecture.

Notations and Tools

Archium: A meta-model and tool developed my Anton Jansen et al

ADDSS: a web based tool developed by Rafael Capilla et al

AREL: a rationale based model developed by Antony Tang et al

DAMSAK: Data Model for Software Architecture Knowledge

developed by Babar et aldeveloped by Babar et al

PAKME : a tool that supports DAMSAK

SEURAT: Software Engineering using Rationale, which integrates tools

for rationale capture, visualization, and use into a standard software

engineering environment

QOC

Questions, Options, Criteria

Questions: key design issues

Options: possible answers

Criteria: assess and compare the optionsCriteria: assess and compare the options

Example

QOC3 Which technology should be used by the user to

communicate locally with the devices which are

located at home?

QOC3 Which technology should be used by the user to

communicate locally with the devices which are

located at home?

QOC Template (Open the Excel File)

ADD: what is interesting to discuss?

1. Granularity of design decisions

2. Dependencies among decisions

3. ADD taken in a collaborative way

4. ADD that uses genetic algorithms in order to find4. ADD that uses genetic algorithms in order to find

the optimal solution

5. Evolving ADD

Granularity…

ADD Question:

� How the FireFighter system components shallcommunicate?

� How is the payment handled?

DI1. How many

gateways can we

place?

Single Gateway

1 Gateway per floor

1 Gateway per

apartment

CostReliability

Availability

DI2. how the

sensors are

connected?Wired

Wireless Wi-Fi

Wireless

ZigBee

Installation

Performance

Availability

Enables decision

DI3.How should

data be broadcasted

Using gateways

Directly through

sensors

Cost

Reliability

Availability

Enables question

Dependencies…

Which device can

the Firefighter Use?

Wearable sensor

Mobile-Wi-Fi

Enables decision

Best way to get a

city map for the

truck manager

Online map

Local offline GPS device

Enables decision

Reliability

Performance

Availability

Dependencies…

Are of various types:

• Excludes

• Requires

• Depends On

• Subsumes

• Enables

• …

Con#1: Which kind of technology is used for node-to-node Con#1: Which kind of technology is used for node-to-node

communication?

� Con#1-Opt#1 : Bluetooth

� Con#1-Opt#2 : Wi-Fi

� Con#1-Opt#3: Zigbee

Con#5: How the WSN infrastructure shall communicate with the trucks and central station?

� Con#5-Opt#1 – 3G

� Con#5-Opt#2 – GPRS

� Con#5-Opt#3 – Wi-Fi

Collaborative Decision Making

http://saw.inf.unisi.ch/drupal/home

Collaborative Decision Making

Optimal Solution to ADD

Tariq Al-Naeem, Ian Gorton, Muhammed Ali Babar, Fethi Rabhi and Boualem Benatallah. “A Quality-Driven

Systematic Approach for Architecting Distributed Software Applications”. In Proc. ICSE 2005.

Evolving ADD

Requirements, Concerns, technology evolves, and so

the associated design decisions.

Con#2: How the nodes should be powered?

• Cr#1 – Cost

• Cr#2 – nodes life duration

• Cr#3 – availability

• Opt#1 : Battery

• Opt#2 : Electrical network