© 1998 by Carnegie Mellon University Intro - page 1 Version 1.1 1 The Architecture Business Cycle...

© 1998 by Carnegie Mellon University

Intro - page 1Version 1.1 1

The Architecture Business The Architecture Business CycleCyclePaul C. Clements

Software Engineering InstituteCarnegie Mellon UniversityPittsburgh, PA 15213-3890

Sponsored by the U.S. Department of Defense© 1998 by Carnegie Mellon University

Carnegie Mellon University

Software Engineering Institute

© 1998 by Carnegie Mellon University Intro - page 2Version 1.1

The Importance of Architecture

To a project• vehicle for stakeholder communication• key to achieving system qualities• basis for development project structure

To an organization• can be reused from project to project• forms a basis for product lines• is a foundation for new market entry

To a community• standard models emerge for mature domains• is a basis for component markets


Definition of Software Architecture

The software architecture of a program or computing system is the structure or structures of the system, which comprise software components, the externally visible properties of those components, and the relationships among them.


Communication Vehicle

Architecture provides a common frame of reference in which competing interests may be exposed and negotiated. • negotiating requirements with users• keeping the customer informed of progress and

cost• implementing management decisions and

allocations


Result of Early Design Decisions -1An architecture defines constraints on an implementation.• implementations must conform to architecture• (global) resource allocation decisions constrain

implementations of individual components• system trade-offs are in the architectural realm


Result of Early Design Decisions -2The architecture dictates organizational structure for development/maintenance efforts. Examples include• division into teams• units for budgeting, planning• basis of work breakdown structure• organization for documentation• organization for CM libraries• basis of integration• basis of test plans, testing• basis of maintenance

Once decided, architecture is extremely hard to change!


Result of Early Design Decisions -3Architecture permits/precludes achievement of a system’s desired quality attributes. For example:

If you desire Examineperformance inter-component communicationmodifiability component responsibilitiessecurity inter-component communication,

specialized components (e. g., kernels)scalability localization of resourcesability to subset inter-component usagereusability inter-component coupling

The architecture influences qualities, but does not guarantee them.


Result of Early Design Decisions -4An architecture helps users reason about and manage change (about 80% of effort in systems occurs after deployment).

Architecture divides all changes into three classes.• local: modifying a single component• non-local: modifying several components• architectural: modifying the gross system topology,

communication, and coordination mechanisms

A good architecture is one in which the most likely changes are also the easiest to make.


Reusable Model

Less is more: It pays to restrict the vocabulary of design alternatives.

Architectural styles serve as that restricted vocabulary of design alternatives.

Working with known styles• reduces learning time• enhances communication• takes advantage of known style properties (e.g.,

performance, security, reliability)


Where do architectures come from?

Architectures are influenced by

• stakeholders of the system(s) being built

• technical and organizational factors

• architect’s background


Stakeholders

Customer: wants low cost, quick delivery, …

End user: wants functionality, usability, ...

Maintainer: wants modifiability, ...

Developer: wants understandability, simple interfaces, ...

Developing organization: amortizing infrastructure, employing personnel, low cost, ...

...


Stakeholders of a System

Marketingstakeholder

Behavior,performance,

security,reliability!

Low cost,keeping people

employed, leveraging existing corporate

assets!

Low cost, timelydelivery, not changed

very often!

Modifiability!Neat features,short time to market,low cost, parity withcompeting products!

Ohhhhh...Architect

Developmentorganization’smanagementstakeholder

End userstakeholder

Maintenanceorganizationstakeholder

Customerstakeholder


Technical Environment

Current trends: today’s information system will likely employ a• database management system• Web browser for delivery and distribution across

platformsThis was not true 10 years ago.

Available technology: decisions on using a centralized or decentralized system depend on processor cost and communication speed; both are changing quantities.


Architect’s Background

Architects develop their mindset from their past experiences. • Prior good experiences will lead to replication

of prior designs.• Prior bad experiences will be avoided in the

new design.


Summary: Influences on the Architect

Architect’s influences

Stakeholders

Developmentorganization

Technicalenvironment

Architect’sexperience

Requirements

Architecture

System

Architect(s)


Factors Influenced by Architectures

Structure of the development organization

Enterprise goals of the development organization

Customer requirements

Architect’s experience

Technical environment

The architecture itself


Architecture Influences the Development Organization StructureShort term: Work units are organized around architectural units for a particular system under construction.

Long term: When company constructs collection of similar systems, organizational units reflect common components • e.g., operating system unit or database unit• especially true in product line organization


Architecture Influences the Development Organization’s Enterprise GoalsDevelopment of a system may establish a foothold in the market niche.

Being known for developing particular kinds of systems becomes a marketing device.

Architecture becomes a leveraging point for additional market opportunities and networking.


Architecture Influences Customer Requirements

Knowledge of similar fielded systems leads customers to ask for particular features.

Customers will alter their requirements on the basis of the availability of existing systems.


Architecture Influences the Architect’s Experience and Technical Environment

Creation of a system affects the architect’s background.

Occasionally, a system or an architecture will affect the technical environment. • the WWW for information systems• the three-tier architecture for database systems


A Cycle of Influences

Architectures and organizations influence each other.• Influences to and from architectures form a

cycle.• An organization can manage this cycle to its

advantage.


Architecture Business Cycle (ABC)

Architect’s influences

Stakeholders

Developmentorganization

Technicalenvironment

Architect’sexperience

Requirements

Architecture

System

Architect(s)


Importance of the ABC

Recognizing architecture as a capital asset• develop it with care• develop it with more than one system in mind• keep it, nurture it, grow it, use it later

Looking for new business opportunities that architecture opens up

Planning and managing the feedback cycle


Example of ABC: Product Lines

Architecture enables entire suite of products to be built more efficiently

Case study: CelsiusTech AB of Sweden


ABC for CelsiusTech

Architect’s influencesCustomer and end userVarious navies

Developing organizationCelsiusTech

Technical environmentAdaObject orientationIterative development

Architect’s experienceReal-time embedded C3I

Requirements(Qualities)Fault toleranceTailorabilityAsset reuseTime to market

Architecture

SystemSS2000 products

Architect(s)


CelsiusTech’s Software ArchitectureTwo dominant styles• layered architecture to separate application-

specific software from software used across the entire product line

• blackboard style to decouple producers and consumers of data

Both styles promote modifiability and reusability.


Layered Architecture

General applications:100% Ada

Common applications:100% Ada

Fundamentals:95% Ada, 5% assembly language

Base system 2000:10% Ada, 90% C

Operator’s console

Targettracking

Firecontrol ASC ECM

Picture compilations

Common application

IPC

Fundamentals

Tacticalconfiguration Database Diagnostics Common

functions

LAN IPC

OS-2000

Base system architecture


Runtime Blackboard Architecture

Similar to A-7E data banker module

COOBData-providing

application HCI

Track information

Updates

RequestsRequests

Updates

Track-ball updates


Current Members of Product FamilySold 55 variants in SS2000 product family• Swedish Goteborg class Coastal Corvettes (KKV) (380

tons)• Danish SF300 class multi-role patrol vessels

(300 tons)• Finnish Rauma class Fast Attack Craft (FAC)

(200 tons)• Australian/New Zealand ANZAC frigates (3225 tons)• Danish Thetis class Ocean Patrol vessels (2700 tons)• Swedish Gotland class A19 submarines (1330 tons)• Pakistani Type 21 class frigates• Republic of Oman patrol vessels• Danish Niels Juel class corvettes


Result of Changes:Shrinking, Predictable Schedules

1986 1988 1990 1992 1994 1996

A

B

C

D

E

F

G

Ships


Result of Changes: Lower Staffing

200

180

160

140

120

100

80

60

40

20

01986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996


Result of Changes: Reuse

Ships

Num

ber

of S

yste

m M

odul

es

Unique application

National application

Modified

Reusable application

Common (verbatim)

140

120

100

80

60

40

20

0A B C D E


ABC Feedback Loop

CelsiusTech is now exploring other domains in which their architecture and product line approach offers promise.

Air defense sector: Surprise! 40% of brand new system could be lifted verbatim from SS2000.


How is architecture-based development different?The architecture-specific aspects of system creation include:• forming an organizational structure that

supports/reflects architecture • architecture design process

- using reference models and domain models - using patterns and styles- building skeletal system, incremental

development• architecture evaluation• checking for conformance


Can We Evaluate an Architecture?Yes. Since architecture• is the key to system qualities• involves decisions relevant to achieving those

qualities• is not a random process

it follows that we can evaluate architectural decisions for their effect on qualities.

Analyzing for system qualities early in the life cycle allows for a comparison of architectural options.


Why evaluate an architecture?

All design involves tradeoffs. Not all tradeoffs are optimal (or anywhere near). Architecture is the earliest artifact where trade-offs are visible.

A evaluation ensures that:• the right questions are asked . . . early• tradeoff points are explicitly identified

Since architecture has such a profound effect on the success/failure of a project, evaluating an architecture is cheap risk insurance.


Cost of architecture evaluations AT&T • 300 full-scale reviews done on projects of 700

staff-days or longer• average cost per review: 70 staff days

Rational Software• 30 reviews done on projects gteq 500 KSLOC each • average cost per review: $50,000

SEI SAAM evaluations• ~15 reviews done on projects ranging from 100

KSLOC to 1,000 KSLOC• average cost per review: 14 to 20 staff-days• average length of review: 2 days


Example of Indirect Staff Costs

Using senior designers for evaluations instead of designing

Loss of productivity (due to reassignment of superior designers)

Time spent training staff in review techniques


Benefits of Architectural ReviewsFive different types of benefits result from holding architectural reviews.1. financial2. forces preparation for review3. early detection of problems4. validation of requirements5. improved architectures


Financial Benefits of Reviews

AT&T estimated that each reviewed project saves 10% of total cost as a result of the review. Thus, a 70-staff-day review of projects of 700 staff-days pays for itself.

Consultants who perform architecture evaluations report 80% repeat business.


Forces Preparation for Review

Documentation/specifications must be provided, hence they must exist or be created.

Some reviews use standard questions, and the architect can prepare ahead to ensure that the architecture scores well.

Reviews make the criteria for evaluation explicit by prioritizing requirements or quality goals.


Early Detection of Problems

The problems that can be found by an architectural level inspection include• unreasonable requirements• performance problems• problems associated with potential future

modifications

The earlier in the life cycle that problems are found, the easier it is to fix them.


Validation of Requirements

Reviews put stakeholders in the same room with each other, often for the first time.• uncovers conflicts and tradeoffs• provides a forum for negotiated resolution of

problems

It often results in the generation of new requirements or the clarification of existing requirements.


Improved Architectures

Development organizations anticipate types of questions raised at reviews and• design architectures with questions in mind• prepare documentation of the type needed at

review• give explicit consideration to qualities to be

reviewed


Review Techniques

There are a variety of techniques for performing architectural reviews; each has a different cost and provides different information.

These techniques fall into one of two basic categories.1. questioning techniques: applied to evaluate

any aspect of an architecture for any given reason

2. measuring techniques: applied to answer questions about a specific quality


Architecture Tradeoff Analysis Method (ATAM)

ATAM is an architecture evaluation method that focuses on multiple quality attributes. In doing so, it:• illuminates points in the architecture where

quality attribute sensitivities & tradeoffs occur• generates a framework for ongoing quantitative

analysis


ATAM and Risks

The point of an ATAM analysis is not to provide precise analyses . . . the point is to discover areas of high potential risk in the architecture.

We want to find trends: correlations between architectural parameters and measurable properties.

These areas can then be made the focus of risk mitigation activities: e.g. further design, further analysis, prototyping.


ATAM Benefits

We have observed a number of benefits to performing ATAM analyses:• stakeholder buy-in and interaction• clarified requirements• improved architecture documentation• documented basis for architectural decisions

And, obviously, improved architectures.


Day 0 Day 1 Day 2

Scenario Elicitation

Architecture Elicitation & Mapping

Analysis

ATAM Steps

The ATAM takes 3 days to execute

Each day follows the same set of steps, but with different emphases:


Day 0: Information Exchange

Purpose: to elicit or refine architectural descriptions, to identify stakeholders, to develop scenarios and initial analyses.

Activities:• identify important quality attributes • document “seed” scenarios• identify stakeholders needed at evaluation• create initial representations of the architecture• define homework for the architect

Outcome: an analyzable architecture


Day 1: Skeleton Analyses

Purpose: to generate a baseline model that characterizes each quality attribute

Activities: [On a per attribute basis]• Elicit attribute-specific usage scenarios• Map important usage scenarios onto relevant

architectural views• Attribute annotation/Skeleton analysis building• Sensitivity point identification• Initial tradeoff point identification

Outcome: qualitative analyses of all important quality attributes


Attribute Analysis Taxonomies

Performance

Stimulus Architecture Parameters Response

Mode Source Frequency Regularity

regular overload Clock interrupt

e.g.,load balancing

e.g.,message arrival

e.g.,missile detected

Internalevent

Externalevent

Periodic Aperiodic

Sporadic Randomparams:period

params:min inter-arrival

interval

params:distribution



Performance


Resource Resource Arbitration Resource Consumption

params:MIPS

CPU memory

networkdevices/sensors

params:bandwidth

params:MB

off-line on-line

cyclic executive fixed

prioritydynamicpriority

queuing policy preemption

policy

locking(non-preemptable)

shared(preemptable

queuing per processor

queue

one-to-one one-to-many

SJF fixed priority

deadline

FIFO



Performance


Latency Throughput Precedence

Responsewindow

Best/avg/worst case

jitter

Criticality

Best/avg/worst case

variabilitywindow

Criticality

Criticality Ordering

Partial Total


Day 2: Finding Tradeoffs

Purpose: to identify growth areas via sensitivities and tradeoffs

Activities: • Attribute-specific growth scenario elicitation

and prioritization• Mapping of growth scenarios onto architecture• Sensitivity point identification• Tradeoff point identification

Outcome: potential sensitivity/tradeoff risk areas of the architecture identified


Experience to date - 1

SAAM• ~15 evaluations to date• supporting artifacts (process model, handbook,

tips and guidance, seed scenarios, artifact examples)

• good for functionality / modifiability investigations

• good for eliciting, prioritizing specific quality requirements

• good for eliciting architectural description


Experience to date - 2

ATAM• 4 evaluations so far, 6-10 more planned• precise method is still firming up• handbook being written• customer feels good value is given• good at non-run-time qualities plus run-time

qualities (SAAM is a procedural subset)


Conclusions

Architecture is a fundamental asset in software development.

Companies who manage it and let it work to their benefit are discovering pay-off.

Architecture-based development must be matured as a discipline.

A key aspect of architecture-based development is architecture evaluation.

© 1998 by Carnegie Mellon University Intro - page 1 Version 1.1 1 The Architecture Business Cycle...

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