The Changing Nature of Feature Interaction

Ken Turner University of StirlingLydie du Bousquet IMAG

Glenn Bruns Bell Labs, Lucent Technologies

Luigi Logrippo Université du QuébecMark Ryan University of Birmingham

29th June 2005

Is FI Dead?Is FI Dead?

Panel Questions

FI - An Outdated Problem?• FI research and the FIW conference

arose from an immediate and specific technological need:• dealing with FI in a very specific telephony

architecture (IN)

• Much FI work was targeted to this need• However researchers have been saying

all along that this is a general problem

The Death of FI?• Is feature interaction dead, rendered

obsolete by new kinds of services?• Does FI exist in VoIP, IVR, Web, Grid?

• Is feature interaction meaningful in modern communications systems?• Are features an old-fashioned IN concept?

• Will feature interaction be replaced by new concepts such as policy conflict?• Are policies replacing features?

The New Face of FI• Is service creation/analysis of greater

interest to industry?• Create effective services, forget analysis?

• How can non-functional feature interactions be considered?• Are known interactions all just behavioural?

• Will feature interaction become an issue for endpoints, not the core network?• Will networks become simple carriers?

• Will new techniques alter the nature of FI?• What about model-driven architecture, AOP?

Lydie du Bousquet IMAG

FI - A Problem in Telephony

• Telephone - a safety critical system• Widely used• POTS + additional features:

• Developed independently• Competitive context

• Types of interaction:• Functional (specification vs. software)• Time delay• Ergonomics (user vs. software/spec)

FI Meaningful Elsewhere ?• FI with car/plane embedded control systems ?

• Yes maybe (Renault?)

• FI in classical software development?• “Service” is not traditional • Components (COTS), Aspects, …

• FI in web services?• Becoming critical/commercial • Is there a “basic service” and additional features?

• FI in ubiquitous software systems?• Too soon: not much used and no “basic service”

• FI in augmented reality ?• Too soon: not much used and no “basic service”

Glenn BrunsBell Labs, Lucent Technologies

Features• Understanding “features” as “call

processing features in telecommunication systems” is much too narrow

• Work in Aspect-Oriented Programming should open our eyes to the broad scope that is possible for this field

• The challenge is to find the fundamental concepts and to see how they are instantiated in different kinds of systems

Economics• At Lucent, “fast” trumps “better”• This attitude probably makes sense

from a business point of view• How much does a undesired feature

interaction cost?

Culture

System Development Computer Science

design

analyze

hard

soft

architect

systems engineer

softwaredeveloper

tester

theory,analysis

design,application

Answers to the Questions• Feature Interaction is not dead – it is

being resuscitated• Policy Conflict provides a new

application area for FI• “Traditional” FIs will remain an issue• Service Creation has always been of

more interest to industry than FI• New approaches such as self-

provisioning will make things interesting

Luigi LogrippoUniversité du Québec en Outaouais

Will there still be FI in VoIP?• Consider the following situations:

• a phone can be simultaneously free and busy

• you can dial a new call when hearing busy• you can connect to someone in a blacklist• anyone can dial in to an existing

conversation • an event under the same preconditions can

yield different results

• If all this and more should be tolerated in VoIP, then there is no point looking for FI

The New Importance of Intention• Since features are freely programmable

in VoIP, there is no technological reason to worry about any of these situations• some users may want it that way; who

knows ...

• FI must be taken to be the undesirable effects of feature composition

• What is undesirable depends on user intentions

Intentions, Policies and Their Inconsistencies

• Some intentions are explicitly stated: these are the policies

• Some are implicit: expectations about system behavior

• FIs are inconsistencies that can occur in specific situations among: • user policies• user intentions

Resolution in context (Tom Gray)

• Application will be 'embedded' in the larger enterprise or social context.

• Resolution must be done within the rules or expectations of that context• a call from a boss is important • a cold call from a salesman is not• for a lawyer, a call from a judge's office requires

immediate attention

• The designer must be aware of the sociological expectations that surround the human activity that application is supporting

• This requires much customization

The World of Web Services: FIs Galore with A Vengeance!

• A phone can ring wrongly without much harm, but the purchase of an expensive item can’t be cancelled as easily!

• Forwarding loops: much worse in effects and prevention, e.g. loops of subcontracts can lead to disastrous economic effects

• Contract interactions: policies of different users clash, making certain contracts impossible, perhaps for futile reasons• How to keep user in the loop for meaningful

resolution

• Security gaps in access control

Infinite loops FIs

• Companies A, B and C have policies where each of them uses the next in a loop as suppliers of parts in excess of inventory

• This can start a chain reaction with potentially disastrous effects!

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Examples byTom Gray

Mark RyanUniversity of Birmingham