Software Product Lines Paolo Ciancarini

Agenda •  Design for reuse •  Software product lines •  Organizational strategies

Motivation Complexity, size, and number of software-intensive systems a major problem for software companies •  routine functionality is custom-written repeatedly

from scratch, over and over •  a quagmire of data formats and applications •  ambiguities and interoperability conflicts not only

across different companies but even among groups within the same company

Family of systems There is a need to •  reduce the development effort •  increase productivity moving from designing single products to producing engineering families of products •  identifying generic solutions to common problems •  building related products by assembling components •  providing universal platforms •  synthesizing systems automatically

Product Line Architecture (PLA) Product Line Architecture: a common design framework that •  standardizes & maximizes reuse potential of all

software artifacts generated during development -  these artifacts include requirements, designs and

patterns, and, of course, actual code components •  specifies common functionality across systems •  clearly identifies variation points

Capturing PLA •  Common core: features common to all products •  FA: features specific to product A •  FB: features specific to product B •  Product A = Common core + FA •  Product B = Common core + FB

Common core

FA Common core

FB

Product A Product B

Lessons from other industries

•  Any customer can have a car painted any colour that he wants so long as it is black” - Henry Ford

Any customer can have a car painted any colour that he wants so long as it is black” Henry Ford

Architecture and standard components

Architecture was simple and flexible Built from standard parts

Standards and diversity What varied? Use features to satisfy diversity of needs Why it worked? Standard architecture and common parts What resulted? Product and assembly lines

The role of architecture in sw

Component based development Software factories exploit component-based development (CBD) •  They engineer applications by composing

prefabricated components in the hope that this will increase software reuse

• Strategy: building software systematically and opportunistically exploting reference architectures about a domain and competitive knowledge for systems in that domain

Domain What is a domain? • Area of expertise with specialized particular tasks • Populated by products with reusable structures

Example: software for a car • Console • Engine • Brakes • …

Domains vs product lines

•  Domain •  Consumer electronics •  Avionics •  Compilers •  Videogames

•  Product line •  Philips Digital TVs •  Boeing 747 Family •  GNU compiler suite •  Games using the

same “engine”

Domains are in the problem space, product lines are in the solution space

VCR Features:"•  Play Tape"•  Rewind Tape"•  Forward Tape"•  Button Control"•  Signal Handling"

Answering machine Features:"•  Play Announcement"•  Record Announcement"•  Rewind Announcement"•  Play Message"•  Record Message"•  Rewind Message"•  Forward Message"•  Display Messages"•  Button Control"•  Signal Handling"

Audio Player Features "•  Play Tape"•  Record Tape"•  Rewind Tape"•  Forward Tape"•  Button Control"•  Signal Handling"

Multimedia Product Line

Product lines

•  Product line technology builds families of products exploiting some common core assets and managing their variability

•  Ex.: Boeing 757 e 767 share 60% of components •  Ex.: Mercedes Benz class E models share 70% •  Scale economies and efficiency •  Integrating rather than creating

Software reuse Why is software reuse critical? •  provides predictable behavior (better testing) •  enables shorter delivery timeframes •  reduces repeated building from scratch of

common functionality

History of the concept dated back to 1950’s •  subroutine libraries •  standardized class libraries

Old ways to reusing software Old definitions of sw reuse include: •  “Re-use is considered as a means to support the

construction of new programs using in a systematical way existing designs, design fragments, program texts, documentation, or other forms of program representation.”

•  “Reusability is the extent to which a software component can be used (with or without adaptation) in multiple problem solutions.”

Reusable assets

Reference Architecture

Architectural Style

Architectural Pattern

Design Pattern

Programming Pattern

Packaged Application

Application Framework

Architectural Mechanism

Legacy Application

Component Library

Component

Pattern Language

Development Method

Reference Model

Architectural Decision

Pattern

Reuse Reuse aspects •  It is not an end in itself but a means to increase

productivity and improve quality • Reusable components are not limited to code • Software components may need adaptation

-  Adaptive design -  Variant design

• Horizontal and vertical reuse

Community & Enterprise Information Portals

Distributed Run-time Middleware

HealthCare Financial Insurance

Metamodel Interoperability

E-Business facilities(Appl. dev., Intelligence, Integration, …)

••• other vertical domains

••• otherfacilities

•••

Benefits By planning ahead in support of families of multiple systems, an organization •  reduces the development time and cost of new

products •  reduces risk and improves quality • manages its legacy assets more efficiently •  evolves a common marketing strategy • makes decisions based on the (value of) the

asset base and the strategic goals

Software product lines (SPL) Definition by Clemens and Northrop (SEI, 2002): • A set of software-intensive systems that share a

common, managed set of features satisfying the specific needs of a particular market segment

•  They are developed from a common set of core assets in a prescribed way

• Example: software for TV sets (Philips)

SPL metamodel

Product lines -  Exploit commonality -  Bound variability

Why SPL work? Product lines amortize the investment in these core assets: •  requirements (and requirements analysis) •  domain models •  software architecture (and design) •  performance engineering •  documentation •  test plans, test cases, and test data •  people: their knowledge and skills •  processes, methods, and tools •  budgets, schedules, and work plans •  components and services

A few success stories •  Celsius tech: family of naval command and control systems

•  Ericsson AXE: family of telecommunications switches

•  Lucent Technologies: 5ESS telecom switch

•  US Naval Undersea Warfare Center: A-7°

•  SALION: Acquisition Management Systems

•  Toshiba: Electric Power Generation Plant

•  BOEING: Bold Stroke Avionics SW Family

•  BOSCH: Gasoline Systems

•  CUMMINS Inc.: Diesel SPL

•  LSI: RAID controller firmware SPL

•  GM: General Motors Powertrain (GMPT)

•  PHILIPS: Medical Systems

•  Nokia: mobile phones

SPL issues • ROI: when are they convenient? • Organization of work • Domain engineering and scoping • Design for reuse of commonality • Control of variability

ROI of SPL

ROI

ROI of SPL

Convenience of Product Lines

29

Key concepts

Organization by product lines

(from Krueger 2009)

Single system perspective

(from Krueger 2009)

Product Line Engineering PL Engineering uses domain-driven, model-based methodology for building software •  Two complementary processes

-  Modeling (domain engineering) -  Development (applications engineering)

"Solution models"

Product Line Engineering

1. Modeling (Domain Engineering, a.k.a Design-for-Reuse)"

Refers to original design, i.e.,the use of first principles"

"Technology"

Domain knowledge"

Dom

ain

Expe

rts &

Dom

ain

Engi

neer

ing

Expe

rts

2. Development (Application Engineering, a.k.a design-with-Reuse)"

refers to routine practice, i.e., the use of known solutions"

Product"

Dom

ain

Expe

rts &

IT te

chni

cian

s Domain Expert New requirements"

Reusable assets Reuse in general needs to be planned for •  create a reusable asset, i.e. one that is fully

documented, has good code and robust scripts; is verified independently with high confidence

•  create a usable asset, i.e. one that is adaptable and that is usable in a variety of simulators

Design for reuse/use involves •  analysis to identify explicitly variations to

anticipate adaptations, and •  design for adaptability, engineered a priori to

create assets for future developments

Problems Design for commonality •  standardizing assets by encapsulating common

features

Analysis of variation • must explicitly identify variations that anticipate

adaptations

Control of variability •  provide assets flexibility without compromising

commonality

Levels of reuse • Domain-independent components

-  Designed for reuse to fit any product (e.g., general purpose class libraries)

• Domain-specific components -  Designed for reuse to fit several different products in a

given market (e.g., multi-media, jpeg encoders, data communications, digital signal processing, ...)

• Product-specific components -  Designed for reuse within a specific “application” (to

generate various instances or products)

SPL: main issues There are several issues to consider • Scoping the SPL (i.e. identify domain and

assets) • Define a reference architecture • Define a PLA •  Identification of reusable components at the

appropriate level of abstraction • Variability management • Architectural compliance • SPL maintenance

What is SPL scoping? •  the initial phase of a SPL, aims to identify

products, features, potential of the market domain and reusable assets

•  determines the viability of the SPL •  maximizes the economical value of the SPL •  Essential factors in SPL: -  Investment -  Management -  Planning -  Business strategy } scoping

Domains!

Systems!

Assets!

Traditional Engineering Model

Individual !domains!

Individual !applications!

Individualimplementations!

Domains!

Systems!

Assets!

SPL Model

•••"

Cn Cn

Cn Cn

Cn

ArchitecturalFramework!

Reusable Component! • F

eatu

res!

• Var

iabi

lity

anal

ysis!

Operator!Plant!

Startup!

Shutdown!

Local! Remote!

Start compressor!

Alarm detected!

Remote!Shutdown!

Local Shutdown!

<<includes>>!

<<extends>>!

<<includes>>!

<<extends>>!

Stop compressor!

<<includes>>!

Operate!

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<<includes>>!<<extends>>!

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CapsuleACapsuleB CapsuleC2 2

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conn

ection

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ork

Class Diagram (domain model)

Colla

bora

tion

Diag

ram

(role

mod

el)

Domain models!

Product Lines and UML Domain Analysis

Identify the “entities” and their relations in the applications domain"

Problem Analysis

Specify basic problem overall functionality, and identify and specify system features"

Solution Analysis

Describe implementation of the solution in terms of interactions between classes and permitted (expected) overall system behavior"

Domain Model (class diagram)

Problem Model (Activity diagram)

Requirements Model (Use Case diagram)

Implementation Model (Collaboration diagram)

Behavioral Model (traces + constraints)

Variability in requirements Optional requirements Cross-cutting aspects Optional scenarios Varying flow of events

Eriksson, Börstler, Borg, Software product line modeling made practical CACM, Dec. 2006

A reference domain for automotive From Bak, Exemplar of Automotive Architecture with Variability, 2010

Software Defined Radios

•  Variation points in radio configuration, board configuration, software configuration

SDRs PL •  By applying product line techniques to

SDRs • Can manage different configurations of the radio -  Deploying components on alternative hosts -  Deployments with

–  No waveforms –  One waveform –  Different combinations of waveforms

• Can show radio in different states as radio starts up or transitions from one waveform to another

SPL according to SEI (5th framework, 2007)

SPL according to SEI

SPL according to SEI

Two approaches to start a SPL •  Proactive: Develop the core assets first

• Develop the scope first and use it as a “mission” statement. • Products come to market quickly with minimum code writing. • Requires upfront investment and predictive knowledge

•  Reactive: Start with one or more products • From them, generate the product line core assets and then the future

products; the scope evolves more dramatically • Much lower cost of entry • The architecture and other core assets must be robust, extensible, and

appropriate to future product line needs

Summary Product Line Architectures, rather than single-product architectures, support systematic reuse •  represent recurrent requirements and

architectures (i.e., components and interfaces) suitable for solving typical problems in a domain

•  depict structures for design related products and provide models for integrating optional/alternative components

•  allow engineers to come up with the “right” solutions quickly and effectively

Architecture-Centric Development Activities

Architecture-specific activities for SPL include: •  creating the business case for the system •  understanding the requirements •  creating and/or selecting the architecture •  documenting and communicating the architecture •  analyzing or evaluating the architecture •  implementing the system based on the architecture •  ensuring that the implementation conforms to the

architecture

From SA to PLA •  Of all a product line’s core assets, the product

line architecture is the most important one for ensuring technical success.

•  If an organization already uses disciplined practices to develop single-product software under the aegis of a software architecture, it is well poised to

•  define a product line architecture •  Identify the core assets •  Build products from those core assets.

Test questions •  What is a software product line? •  What is a product line architecture? •  What is variability management?

References •  Clemens & Northrop, Software Product Lines, Addison Wesley, 2002

•  Gomaa, Designing SPL with UML, Addison Wesley, 2005

•  Pohl & Böckle, SPL Engineering: foundations, principles, and techniques, Springer 2005

•  vanderLinden & Schmid & Rommes, SPL in action, Springer, 2007

•  van Gurp & Bosch & Svahnberg, On the notion of variability in SPL, Conf. on Sw Architecture, 2001

•  Eriksson, Bostler, Borg, Software product line modeling made practical. An example from the Swedish defense industry, CACM 2006

•  Krueger & Jackson, Requirements engineering for systems and software product lines, White paper IBM Rationa,l 2009

Conferences •  SPLC 2011, Munich, Germany •  Workshop on Variability in Software Product Line

Architectures •  Wokshop on Product LinE Approaches in Software

Engineering (PLEASE)

Sites •  www.sei.cmu.edu/productlines •  www.biglever.com

Questions?