4. Theory of change propagation

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4. Theory of change propagation

• Let C be a set of classes
• For b,c ? C, b ? c,
• b,c is interoperation (interactions)
• Type-instance, inheritance, etc.
• ltb,cgt is mark
• b was visited (changed), c will be visited
  (changed) denoted by an arrow
• Evolving interoperation graph (eig) is a set E of
  interoperations and marks
• ltb,cgt ? E implies b,c ? E.
• Marked interaction can be inconsistent

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neighborhood

• all interactions, incoming, outgoing marks of b
• G(b) b,c b,c ? E
• M(b) ltc,bgt ltc,bgt ? E incoming
• M(b) ltb,cgt ltb,cgt ? E outgoing
• E(b) G(b) ? M(b) ? M(b)
• (evolving neighborhood of b)

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visit

• visit E' (E - E(b)) ? E'(b')
• E(b) old neighborhood
• E(b) new class and new neighborhood
• marks point away from b in the new neghborhood

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change propagation

• sequence of eigs E1, E2, En
• starts and ends with unmarked graphs
• marked graphs in the middle
• ltEi, Ei1gt is a visit
• or backtrack
• for some k, 0 lt k lt i, Ei1 Ek

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Visit to a class (graphically)
Change propagates
Change does not propagate
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Change propagation types

• Class A changes and interacts with class B
• B changes and propagates change to its neighbors
• B does not change and does not propagate change
• B does not change and propagates change to its
  neighbors

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order of implementation

• The concepts must be implemented in the order of
  their dependency
• tax is dependent on item
• tax without an item is meaningless
• the implementation of item must precede the
  implementation of tax
• mutually dependent concepts must be implemented
  at the same time
• example store and register

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mutually independent concepts

• can be introduced in arbitrary order
• example several cashiers and
• it is more important to deal correctly with taxes
  than to support several cashiers
• application with support for taxes is already
  usable in stores with one cashier

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observations

• overhead of change
• concept location and change propagations
• small changes have the same overhead
• decreased efficiency of the work
• increased likelihood of errors
• big changes overload the cognitive capabilities
  of the programmers
• increased likelihood of errors