Vakgroep Informatietechnologie – IBCN

Software EngineeringProf.Dr.ir. F. Gielen

Quality Attribute Workshop

Workshop Overview

1. Build the Quality Attribute Tree

2. Elaborate 3 quality attribute scenarios

3. Map to architecture tactics

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Quality Attributes

Quality Attributes are non functional requirements related to the ABC.

They are documented using Quality Attribute Scenarios. (NOT in UML)

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The Utility Tree

Quality Attribute Challenges: Characterizing, Quantification … Selection & Priority

The Utility tree is top-down approach for: characterizing the quality attribute requirements –

make them less abstract. E.g. the system has to be fast …

selecting the most important quality goals to be the high-level nodes (performance, security, availability, modificability, maintanibility)

the leaves of the tree are quality scenarios evaluated by importance (success of the system) and difficulty (architect’s assessment).

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Utility Tree Example

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ROOT LVL 1 LVL 2 LVL 3 Short Scenario:• Stimulus• Context• Response

Importance:• business• technical

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Generating a Quality Attribute Utility Tree

Quality attributes are articulated in detail:Goal: Elicit the most important quality attributes as short

scenarios.

Root: Utility is an expression of the benefit to the user or customer.

Level 1: Quality attributes are the second level. The initial set comes from the business drivers

Level 2: Attribute Refinements. Level 3: Short scenarios (stimulus, context, response)

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Lvl 2 : Attribute Refinement

Make the quality attribute less abstract by characterizing them based on attribute taxonomies and generic QAS.

Info can be found in standards (ISO 25010) Example : Performance

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LvL 3: Short Scenario Prioritisation

1. Describe a number of short scenarios based on attribute refinements.

2. Project decision makers give a relative ranking based on importance (business goal).

3. Architect gives a ranking based on difficulty to satisfy the scenario. (technical goal)

4. Each scenario has a (H,H), (H,M),…(L,M),(L,L) priority assigned.

5. Based on this a selection of scenarios is made for the purpose of elaboration.

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Example : JBOSS Quality Attributes

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Workshop Overview

1. Build the Quality Attribute Tree

2. Elaborate 3 quality attribute scenarios

3. Map to architecture tactics

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Generic QA Scenarios

Every quality attribute has a generic scenario. It contains the characteristics and the common

vocabulary used to describe each of the sections in the specific QA scenario.

Examples: Performance Modifiability Usability Security

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Performance QAS

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Specific Scenarios

A Quality Attribute Scenario describes:

SOURCE: who or what STIMULUS: does something ARTIFACT: to the system or part of it ENVIRONMENT: under certain conditions RESPONES: how the system reacts MEASURE: how you can measure this

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Performance Generic QAS

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Source

External

Internal

events

Environment

Normal mode

Overload mode

Reduced Capacity mode

Measure

Latency

Deadline

Throughput

Capacity

Jitter

Miss rate

Response

Change in system mode

or

service level.

Stimulus

Periodic

Sporadic

Stochastic

Bursty

events

Artifact

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Modifiabililty Generic QAS

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SourceDeveloper

Sys admin

User

Environment- Design

- Build

- Deploy

- Runtime

Measure

# of artifacts

Effort

Time

Cost

Impact

New defects

Response- Change,

- Test

- Deploy

StimulusModify:

- Functions

- Qualities

- Platform

- Technology

- Scale/Scope

ArtifactCode, Data, Interfaces

Components,

Resources, Configs ..

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Example : Public Transport Signage

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Availability QAS :

Q: What is the architectural impact of this requirement ?

SOURCE who or what A random event

STIMULUS does something ... causes a failure

ARTIFACT to the system or part of it ... to the communication system

ENVIRONMENT under certain conditions ...during normal operations

RESPONSE how the system reacts All displays must start showing scheduled arrival times for all buses

MEASURE how you can measure this ... Within 30 seconds of failure detection

Workshop Overview

1. Build the Quality Attribute Tree

2. Elaborate 3 quality attribute scenarios

3. Map to architecture tactics

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Performance Tactics: Summary

Performance

Resource

Demand Resource

Management

Resource

Arbitration

Response

generated

within

Time Constraints

Event

Arrives

•Increase computational efficiency

•Reduce computational overhead

•Manage Event Rate

•Control Frequency of Sampling

•Introduce concurrency

•Maintain multiple copies

•Increase available resources

•Scheduling

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Modifiability Tactics: summary

Change

Request

Arrives

Changes made,

Tested and Deployed

on Time,

within Budget

Modifiability

Reduce

SizeIncrease

Cohesion

Defer

Binding Time

Encapsulation

Wrap

Restrict communication paths

Use an intermediary

Split modules

Increase Semantic Coherence

Abstract Common Services

Reduce

Coupling

QAW: Quality Attribute Workshop

1. Select the quality attributes that provide utility to the user. (lvl1):1. Verify the generic QAS & ISO 25015

2. Refine the attributes of this quality (lvl2):1. Verify attribute taxonomies (ISO25010)

3. Provide short scenario’s (lvl3)

4. Assign priorities to the scenarios.

5. Elaborate the most important scenarios (6 parts) .

6. Map to tactics

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QAW Resources

Quality Attributes Technical Report CMU/SEI-95-TR-021

Summary of generic QA scenario’s

ISO 25010 publication: SQuaRE quality model

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