Topics
 Evaluating Software Architectures

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What an evaluation should tell
What can be examined, What Can’t
 ATAM
Next Time: Case Study: the Nightingale System
Ref: The “Evaluating Architectures” book and Chap 11
October 22, 2003

Last Time
 Analysis of Architectures
 Why, When, Cost/Benefits
 Techniques
 Properties of Successful Evaluations
New: Analysis of Architectures
 Why, When, Cost/Benefits
 Techniques
 Properties of Successful Evaluations
Next time:
References:
– 2 – CSCE 742 Fall 03

Why evaluate architectures?
When do we Evaluate?
Cost / Benefits of Evaluation of SA
Non-Financial Benefits
EvaluationTechniques
 Active Design Review,” SAAM (SA Analysis Method), ATAM
(Architecture Tradeoff Analysis Method), CBAM (2001/SEI) –
Cost Benefit Analysis Method
Planned or Unplanned Evaluations
Properties of Successful Evaluations
Results of an Evaluation
Principles behind the Agile Manifesto
Architecture Tradeoff Analysis Method (ATAM)
Conceptual Flow ATAM
– 3 – CSCE 742 Fall 03

ATAM is based upon a set of attribute-specific measures of the system
 Analytic measures, based upon formal models
 Performance
 Availability
 Qualitative measures, based upon formal inspections
 Modifiability
 Safety
 security
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 clarified quality attribute requirements
 improved architecture documentation
 documented basis for architectural decisions
 identified risks early in the life-cycle
 increased communication among stakeholders
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– 6 –

From the architecture we can’t tell if the resulting system will meet all of its quality goals
Why?
Usability  largely determined by user interface
User interface is typically at lower level than SA
 UMLi http://www.ksl.stanford.edu/people/pp/papers/PinheirodaSilva_ksl_02_04.pdf
ATAM concentrates on evaluating a SA based on certain quality attributes
– 7 – CSCE 742 Fall 03

Performance
Reliability
Availability
Security
Modifiability
Portability
Functionality
Variability – how well the architecture can be expanded to produce new SAs in preplanned ways ( important for product lines)
Subsetability
Conceptual integrity
– 8 – CSCE 742 Fall 03

There are some quality attributes that are just to vague to be used as the basis for an evaluation.
Examples
 “The system must be robust.”
 “The system shall be highly modifiable.”
Quality attributes are evaluated in some context
 A system is modifiable wrt a specific kind of change.
 A system is secure wrt a specific kind of threat.
– 9 – CSCE 742 Fall 03

1.
Prioritized statement of quality attribute requirements

“You've got to be very careful if you don't know where you're going, because you might not get there.” Yogi Berra
 Yogi also said "I didn't really say everything I said."
2.
Mapping of approaches to quality attributes
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How the architectural approaches will achieve or fail to achieve quality attributes
Provides some “rationale” for the architecture
3.
Risks and non-risks
 Risks are potentially problematic architectural decisions
There are more for each specific analysis technique. We will consider ATAM soon.
– 10 – CSCE 742 Fall 03

Documenting risks and non-risks consists of:
 An architectural decision (that has not been made)
 A specific quality attribute response being addressed by that decision
 A rationale for the positive or negative effect that the decision has on satisfying the quality attribute
– 11 – CSCE 742 Fall 03

The rules for writing business logic modules in the second tier of your three tier client-server system are not clearly articulated. (decision to be made)
This could result in replication of functionality thereby compromising modifiability of the third tier (a quality attribute response and its consequences)
Unarticulated rules for writing business logic can result in unintended and undesired coupling of components (rationale for the negative effect)
*Example from: Evaluating Software Architectures: Methods and Case
– 12 –
Studies by Clements, Kazman and Klein
CSCE 742 Fall 03

Assuming message arrival rates of once per second, a processing time of less than 30 milliseconds and the existence of one higher priority process (the architectural decisions)
A one-second soft deadline seems appropriate (the quality attribute response and its consequence)
Since the arrival rate is bounded and the preemptive effects of higher priority processes and known and can be accommodated (the rationale)
*Example from: Evaluating Software Architectures: Methods and Case
– 13 –
Studies by Clements, Kazman and Klein
CSCE 742 Fall 03

 The evaluation team
 Team leader –
 Evaluation leader
 Scenario scribe
 Proceedings scribe
 Timekeeper
 Process observer
 Process enforcer
 Questioner
 Project Decision makers – people empowered to speak for the development project
 Architecture stakeholders –
 including developers, testers, …,
 users,
– 14 –
 builders of systems interacting with this one CSCE 742 Fall 03

Team leader
 Sets up evaluation (set evaluation contract)
 forms team
 interfaces with client
 Oversees the writing of the evaluation report
Evaluation leader
 Runs the evaluation
 Facilitates elicitation of scenarios
 Administers selection and prioritization of scenarios process
 Facilitates evaluation of scenarios against architecture
Scenario scribe
 Records scenarios on a flip chart
 Captures (and insists on) agreed wording
Proceedings scribe
– 15 – CSCE 742 Fall 03

Proceedings scribe
 Captures proceedings in electronic form
 Raw scenarios with motivating issues
 Resolution of each scenario when applied to the architecture
 Generates a list of adopted scenaios
Timekeeper
 Helps evaluation leader stay on schedule
 Controls the time devoted to each scenario
Process observer
 Keeps notes on how the evaluation process could be improved
Process enforcer – helps the evaluation leader stay “on process”
Questioner raises issues of architectural interest stakeholders may not have thought of
– 16 – CSCE 742 Fall 03

A Concise presentation of the architecture
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Frequently there is “too much”
ATAM will force a “one hour” presentation of the architecture forcing it to be concise and clear
Articulation of Business Goals
Quality requirements in terms of collections of scenarios
Mapping of architectural decisions to quality attribute requirements
A set sensitivity and tradeoff points
 Eg. A backup database positively affects reliability
(sensitivity point with respect to reliability)
 However it negatively affects performance (tradeoff)
– 17 – CSCE 742 Fall 03

A set of risks and non-risks
 A risk is an architectural decision that may lead to undesirable consequences with respect to a stated quality attribute requirement
 A non-risk is an architectural decision that, after analysis, is deemed to be safe

Identified risks can form the basis of a “architectural risk mitigation” plan
A set of risk themes
 Examine the collection of risks produced looking for themes that are the result of systematic weaknesses in the architecture
Other outputs – more documentation, rationale, sense of community between stakeholders, architect, …
– 18 – CSCE 742 Fall 03

Phase Activity
0 Preparation
Participants
Team leadership/key project decision makers
Duration
Over a few weeks
1 Evaluation
3 Follow-up
Evaluation team and project decision makers
2 Evaluation with Ditto + stakeholders
Stakeholders
1 day + hiatus of 2 to 3 weeks
2 days
Evaluation team and client 1 week
– 19 – CSCE 742 Fall 03

1.
Present the ATAM
2.
Present Business drivers
3.
Present Architecture
4.
Identify architectural approaches
5.
Generate quality attribute utility tree
6.
Analyze architectural approaches
 Hiatus and start of phase 2
7.
Brainstorm and prioritize scenarios
8.
Analyze architectural approaches
9.
Present results
– 20 – CSCE 742 Fall 03

Client – someone who can exercise control of the project whose architecture is being evaluated
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
Perhaps a manger
Perhaps someone in an organization considering a purchase
Issues that must be resolved in Phase 0:
1.
The client must understand the evaluation method and process (give them a book, make them a video)
2.
The client should describe the system and architecture. A “go/no-go” decision is made here by the evaluation team leader.
3.
Statement of work is negotiated
4.
Issues of proprietary information resolved
– 21 – CSCE 742 Fall 03

Forming the evaluation team
Holding an evaluation kickoff meeting
Assignment of roles
 Good idea to not get into ruts; try varying assignments
 Roles not necessarily one-to-one
 The minimum size evaluation team is 4
 One person can be process observer, timekeeper and questioner

Team leader’s responsibilities are mostly “outside” the evaluation. He can double up. (Often the evaluation leader.)
 Questioners should be chosen to represent the spectrum of expertise in performance, modifiability, …
– 22 – CSCE 742 Fall 03

Organizational meeting of evaluation team and key project personnel
 Form schedule
 The right people attend the meetings
 They are prepared (know what is expected of them)
 They have the right attitude
 Besides carrying out the steps the team needs to gather as much information as possible to determine
 Whether the remainder of the evaluation is feasible
 Whether more architectural documentation is required
 Which stakeholders should be present for phase 2
– 23 – CSCE 742 Fall 03

Evaluation leader presents the ATAM to all participants
 To explain the process
 To answer questions
 To set the context and expectations for the process
 Using standard presentation discuss ATAM steps in brief and outputs of the evaluation
– 24 – CSCE 742 Fall 03

Figure 3.9 from “Evaluating Software Architectures:
Methods and Case Studies,” by Clements, Kazman and Klein
– 25 – CSCE 742 Fall 03

Everyone needs to understand the primary business drivers motivating/guiding the development of the system
A project decision maker presents a system overview from the business perspective
 The system’s functionality
 Relevant constraints: technical, managerial, economic, or political
 Business goals
 Major stakeholders
 The architectural drivers – the quality attributes that shape the architecture
– 26 – CSCE 742 Fall 03

The lead architect makes the presentation at the appropriate level of detail
Architecture Presentation (~20 slides; 60 minutes)
 Architectural drivers and existing standrards/models/approaches for meeting (2-3 slides)
 Important Architectural Information (4-8 slides)
 Context diagram
 Module or layer view
 Component and connector view
 Deployment view
 Architectural approaches, patterns, or tactics employed
– 27 – CSCE 742 Fall 03

 Architectural approaches, patterns, or tactics employed
 Use of COTS (commercial off the shelf) products
 Trace of 1-3 most important use cases scenarios
 Trace of 1-3 most important change scenarios
 Architectural issues/risks with respect to meeting the driving architectural requirements
 Glossary
Should have a high signal to noise ratio, don’t get bogged down too deeply in details
Should cover technical constraints such as operating system, hardware and middleware
– 28 – CSCE 742 Fall 03

The ATAM analyzes an architecture by focusing on its architectural approaches
Captured by not analyzed (here) by the evaluation team
The evaluation team should explicitly asked the architect to name these
– 29 – CSCE 742 Fall 03

– 30 – CSCE 742 Fall 03

Types of Scenarios:
 Use case scenarios
 The user wants to examine budgetary data
 Growth scenarios
 Change the maximum number of tracks from 150 to 200 and keep the latency of disk to screen at 200ms or less
 Exploratory scenarios
 Switch the OS from Unix to Windows
 Improve availability from 98% to 99.99%
– 31 – CSCE 742 Fall 03

The evaluation team examines the highest priority scenarios one at a time and the architect is asked how the architecture supports each one.
– 32 – CSCE 742 Fall 03

– 33 – CSCE 742 Fall 03

The Hiatus
 Evaluation team distills what has been learned and informally contacts architecture for more information where needed
After
– 34 – CSCE 742 Fall 03

“Evaluating Software Architectures: Methods and Case
Studies
by Clements, Kazman and Klein, published by Addison-Wesley, 2002. Part of the SEI Series in
Software Engineering.
SEI Software Architecture publications
 http://www.sei.cmu.edu/ata/pub_by_topic.html
– 35 – CSCE 742 Fall 03