Software Engineering and Further Aspects of Database Design

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Software EngineeringandFurther Aspects of
Database Design
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Wicked Problems

• The pointthe traditional approach to software
  engineering is fundamentally unsuitable. A
  different approach is needed.
• We will use an approach that recognizes the
  nature of software designits usually a wicked
  problem. Our approach will seem undisciplined
  but is superior to the traditional approach.
• We will employ just-in-time database design as
  the central coordination mechanism for the
  project.

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Important MCC Study

• MCC studied how experienced, highly successful
  designers of elevators approached design problems
• During actual design, they watched their behavior
  to observe the phases of design and the sequence
  in which they executed the various phases
• MCC researchers found that the actual approach
  used was very different from formal methods that
  we advocated
• The designers transitioned regularly back and
  forth from one phase to another

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Traditional Approach
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What Is Actually Done
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Tame Problem

• Has requirements that are well defined at the
  outset
• Requirements stay constant during the design and
  implementation
• Stakeholder interests are well established and
  constant during the effort
• The solution is known and recognizable

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Wicked Problem

• You don't understand the problem until you have
  developed a solution.
• Multiple stakeholders
• You may need to adjust the requirements based on
  solutions that can be developed
• Constraints on the solution change over time.
• Stakeholders come and go, change minds, fail to
  communicate, change the rules.
• No definitive Problem, no definitive Solution.

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Which Problems Are Wicked?

• Design and launch a satellite
• Design a new car
• Design a bridge over the Potomac
• Route a new highway
• Reorganize your department
• Develop a new kind of bullet-resistant glass that
  is half the weight of current products for the
  same bullet resistance

• Design an electric motor, given power, speed,
  weight requirements
• Devise a mission statement for your company
• Design a personal information manager for your
  own use
• Design a folksonomic collaborative Web site

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Most software development efforts of interesting
scope today are wicked problems.
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Whats A Wicked Problem

• A wicked problem is an evolving set of
  interlocking issues and constraints. A linear
  approach to solving a wicked problem simply will
  not work.

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How We Will Proceed on the Project

• Involve everyone customers, developers, system
  engineers
• Lots of dialogue
• Flexibility in order of work
• Development teams choose what they program,
  encourage SET to complete database design in that
  area
• Encourage Openness
• Teamwork is facilitated
• Completely inform everyone
• All emails about project to every member
• Avoid time-wasting struggles
• Personal disputes are forbidden
• Look at possible solutions early
• Early mockup of final site

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Guidelines

• All phases of work start on Day 1
• Every member of each group does a major favor,
  early, for every other member
• Group decisions guide just-in-time database
  design work
• All email communications must go to all project
  members
• Criticism of another project member is absolutely
  forbidden

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System Engineering Team

• Produces no code of their own
• Responsible for database design, overall project
  success
• Organizes schedule
• Establishes procedures for code submission,
  release of systems
• Conducts system testing
• Administers Web site contents

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Database Design TopicNatural vs. Generated Keys
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Definitions

• Natural keya key that occurs in the data, that
  serves as a unique identifier for rows
• Generated keya key that is generated in order to
  make rows unique

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Generated Keys

• In some organizations, programmers have the idea
  that generated keys should be included in every
  relation
• Thats a fine idea for an Excel spreadsheet but
  it shows a misunderstanding of what a relation is
  and what a tuple is
• Tuples are naturally unique because each one
  corresponds to a distinct instance of an entity
  type in the real world. You dont have to add
  anything to make them unique.

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When to Use Generated Keys

• Sometimes you have a compound key that is very
  long
• Lots of queries will be very complicated and
  tables with foreign keys will copy most of
  another table
• As a guideline, never use a generated key unless
  it is a surrogate for a compound key of at least
  three columns