Large Scale Software Development

Bart Massey 2013-11-26

Overview

• Daily WTF CSoD: http://thedailywtf.com/Articles/How-the-Big-Companies-Do-It.aspx
• Large Scale Software Development
• Risk Management
• Open Source Software Development

Large Scale Software Development

• Everything is harder

• Some bits are fundamentally different

• Key topics:

  • Software Process Management

  • Software Product Lines and Versioning

  • Large Scale Deployment

  • Software Maintenance

Software Process Management

• Process must be well-controlled

• Pick a "Process Model" and stick with it

  • Waterfall (incremental and iterative)

  • "Agile"

  • ???

• The "V Model"

• The "Spiral Model"

The V Model

• Discussed previously

• Fundamental idea: during an activity, construct the V&V plan for that activity

  Planning ->                       Deployment V&V
      \                              /
    Requirements ->               System V&V
        \                          /
      Architecture ->           Integration V&V
          \                      /
        Detailed Design ->    Module V&V
            \                  /
          Implementation -> Unit V&V
              \              /
               \            /
  

• Works well on several levels

The Spiral Model

• Some projects are extra-risky. This threatens fail-early

• Idea: be iterative at a higher level

                                |
       1. Determine Objectives  |  2. Identify and Resolve Risks
                                |
     ---------------------------+-----------------------------
                                |
       4. Plan Next Iteration   |  3. Development and Test
                                |
  

• "Spiral" outward through these steps until full scope is reached

SEI CMM

• Capabilities Maturity Model: Example of process improvement

  • Initial (1)
  • Repeatable (2)
  • Defined (3)
  • Managed (4)
  • Optimizing (5)

• At each level, a number of specific process characteristics are required

• Example of CMM L5 organization: NASA Space Shuttle SW group

Versioning

• Large projects rarely have a single product even at one point in time

  • Multiple simultaneous development threads
  • Multiple configurations

• Automated frameworks are key for management

  • Able to build and test all versions automatically
  • Able to track configurations and config change history

• Large products must be built for size (c.f. Brooks' "Programming Systems Product"

Software Product Lines

• Sometimes projects are built with a great deal of project-specific infrastructure

• Keeping track of interrelationships and "soft SKUs" requires its own infrastructure

Large Scale Deployment

• Number one rule: customer contact is... expensive

• Number two rule: OOBE must be flawless

• Risk management is key

  • Incremental deployment
  • Parallel deployment
  • Deployment team resource management

Software Maintenance

• Only one kind of unmaintained software

• Perhaps biggest effort in software life cycle

• See rule number one

• Infrastructure is crucial

  • Adequate staffing
  • Adequate knowledge transfer
  • Workable issue tracking system

Risk Management

• All risks are magnified in a large project

• Risk equation:

  R = P x S
  

  where P is the probability of the risk and S is the severity

• Key document: Risk Management Plan

  • Identify all risks of significant R value (including a few highly improbable or not severe ones)

  • For each risk, have plans for what to do if it materializes

  • Maintain the RMP over time

Open Source Software Development

• An "alternate" model for large projects

  • OK, not that alternate

• Key ideas:

  • Asynchrony and non-locality force a lot of large project practices anyhow
  • Some hard constraints removed
  • Some easy opportunites

• Key practices:

  • Code-centric development
  • Tool-based practices
  • Intensive user feedback