Software Engineering

1
Software Engineering

• November 7, 2001
• Rationale Management
• Joseph Conron
• Computer Science Department
• New York University
• jconron_at_cs.nyu.edu

2
What is rationale?

• Rationale is the reasoning that lead to the
  system.
• Rationale includes
• Issues that were addressed,
• Alternatives that were considered,
• Decisions that were made to resolve the issues,
• Criteria that were used to guide decisions, and
• Debate developers went through to reach a
  decision.

3
Rationale helps deal with change

• Improve maintenance support
• Provide maintainers with design context
• Improve learning
• New staff can learn the design by replaying the
  decisions that produced it
• Improve analysis and design
• Avoid duplicate evaluation of poor alternatives
• Make consistent and explicit trade-off

4
Levels of rationale

• No rationale captured
• Rationale is only present in memos, online
  communication, developers memory
• Rationale reconstruction
• Rationale is documented in a document justifying
  the final design
• Rationale capture
• Rationale is documented during design as it is
  developed
• Rationale integration
• Rationale drives the design

5
Centralized traffic control

• CTC systems enable dispatchers to monitor and
  control trains remotely
• CTC allows the planning of routes and re-planning
  in case of problems

6
Centralized traffic control (2)

• CTC systems are ideal examples of rationale
  capture
• Long lived systems (some systems include relays
  installed decades ago)
• Extended maintenance life cycle
• Downtime is expensive (although not safety
  critical)
• Low tolerance for bugs
• Transition to mature technology
• Initial developers are not available

7
Issues

• Issues are concrete problems which usually do not
  have a unique, correct solution.
• Issues are phrased as questions.

How should track sections be displayed?
How should the dispatcher input commands?
8
Proposals

• Proposals are possible alternatives to issues.
• One proposal can be shared across multiple issues.

9
Consequent issue

• Consequent issues are issues raised by the
  introduction of a proposal.

display?Issue
addressed by
addressed by
addressed by
pointclickProposal
10
Criteria

• A criteria represent a goodness measure.
• Criteria are often design goals or nonfunctional
  requirements.

11
Arguments

• Arguments represent the debate developers went
  through to arrive to resolve the issue.
• Arguments can support or oppose any other part of
  the rationale.
• Arguments constitute the most part of rationale.

12
Arguments (2)
13
Resolutions

• Resolutions represent decisions.
• A resolution summarizes the selected alternative
  and the supporting argument.
• A resolved issue is said to be closed.
• A resolved issue can be re-opened if necessary,
  in which case the resolution is demoted.

14
Resolutions (2)
15
Representing rationale issue models
resolves
Issue?
Resolution.
is a consequence
responds
meets
fails -
supports objects to -
supports objects to -
Argument!
16
Representing rationale (contd)

• Many issue models have been proposed
• IBIS, QOC, DRL, WinWin
• Similar in their essence
• Differ in the amount of detail that can be
  captured
• Challenges
• Require tool support for capture and access
• Require integration with CASE and project
  management tools
• Require integration with methodology

17
Open issues

• Formalizing knowledge is costly.
• Maintaining a consistent design model is
  expensive.
• Capturing and maintaining its rationale is worse.
  
• The benefits of rationale are not perceived by
  current developers.
• If the person who does the work is not the one
  who benefits from it, the work will have lower
  priority.
• 40-90 of off-the-shelf software projects are
  terminated before the product ships.
• Capturing rationale is usually disruptive.
• Current approaches do not scale to real problems

18
Summary

• Capturing rationale is critical
• Argumentation of alternatives
• Explicit design criteria
• Information relevant for future change
• Issue models provide a good representation
• Offer a structured solution to capture rationale
• Make it easier to browse rationale information
• Rationale needs to be integrated through out the
  process
• Provide a short term incentive
• Decrease setup cost