Is AP a sound methodology compared to OO?

1
Is AP a sound methodology compared to OO?

• A comparison of effort and static analysis
  support when working with AP and OO

2
Motivation

• AP has the AI flavor that it automatically
  transforms programs when the context (class
  graph) changes.
• Some people see this power as a danger.
• We point out that when a proper software
  engineering process is followed there is no
  danger.
• Powerful tools can be used in bad ways.

3
Motivation

• Some people feel that AP tools cannot give the
  same static error messages as OO tools. We show
  that this is not the case.

4
What does AP save during evolution? Terminology.

• T(G) traversal methods for G.
• TG(G,S) traversal graph for G and S.
• Compatible(G,S) Is G compatible with S? For all
  edges (x,y) in S there is a path in G from x to y.

5
What does AP save during evolution? Terminology.

• Diff(TG1, TG2), Diff(T(G1), T(G2)) list
  differences for each node.
• Errors(G2,T(G1)) compiler error messages
• Errors(G2, G1) if G1 has an edge (A,B) then G2
  has such an edge, otherwise report error.

6
For AP library

• Errors(G2, G1) if G1 has an edge (A,B) then G2
  has such an edge, otherwise report error.
• Intent Lists all the places where the old
  traversal (G1) brakes if used in new class graph
  (G2).
• Information for test specification check whether
  redirections are correct.

7
For AP library

• Errors(G2, G1) if G1 has an edge (A,B) then G2
  has such an edge, otherwise report error.
• Note The Errors(G2,G1) function is similar to
  checking whether G1 is an instance of G2.

8
What does AP save during evolution?
Written by user
Inspected by user, generated by compiler

• Both Class graphs G1 and G2. Traversal methods
  T(G1) and T(G2) to be tested.
• AP Strategy graphs S1, S2. Traversal graphs
  TG(G1,S1) producing T(G1) and TG(G2,S2)
  producing T(G2). Compatible(G1,S1),
  Compatible(G2,S2). Errors(G2, Graph(TG(G1,S1))).
  Diff(TG(G1,S1), TG (G2,S2)).
• OO T(G1) and T(G2). Compatible(G2,T(G2)). Errors
  (G2,T(G1)). Diff(T(G1), T(G2)).

9
Comparing AP versus OO during evolution effort
Written by user
Inspected by user, generated by compiler

• AP
• S1,TS ? S2
• Compatible(G2,S2)
• Errors(G2, Graph(TG(G1,S1)))
• Diff (TG(G1,S1), TG(G2,S2))

• OO
• T(G1),TS ? T(G2)
• Compatible(G2,T(G2))
• Errors(G2,T(G1))
• Diff (T(G1), T(G2))

Common G1 ? G2, test(T(G1)), test(T(G2)), trav.
change spec. TS Comparable effort testing
AP less effort on average
10
Comparing AP versus OO during evolution static
checking
Written by user
Inspected by user, generated by compiler

• AP
• S1,TS ? S2
• Compatible(G2,S2)
• Errors(G2, Graph(TG(G1,S1)))
• Diff (TG(G1,S1), TG(G2,S2))

• OO
• T(G1),TS ? T(G2)
• Compatible(G2,T(G2))
• Errors(G2,T(G1))
• Diff (T(G1), T(G2))

Common G1 ? G2, test(T(G1)), test(T(G2)), trav.
change spec. TS Comparable information
11
Example
S1
A
C
S2
A
B
C
A
B
C
K
A
B
C
G1
G2
X
K
A
B
C
A
B
C
T(G2)
T(G1)
AP
OO
A
B
C
Errors
A
B
C
Errors
K
K
C
C
A
B
A
B
Diff
Diff
12
Example

• S1 from A to C
• G1A,BB,C
• T(G1)A B C
• Compatible yes
• Errors no B,C
• Diff B,CgtB,K. new K,C

• S2 from A via B to C
• G2A,BA,XB,KK,CX,C
• T(G2) A B K C
• Compatible yes
• Errors no B,C
• DiffB,CgtB,K. new K,C

13
Comparison AP versus OO during evolution

• Static analysis information
• AP gives similar static information as OO
• Evolution effort
• AP never worse than OO
• in many cases AP less effort
• Danger of wrong traversals testing needed.
• OO possibility of errors not detected
  statically.
• AP possibility of strategy being wrong. If
  strategy correct, traversal guaranteed to be
  correct.

14
Comparison AP versus OO during evolution

• If class graph changes, it is necessary to
  re-test generated program.
• Whether program is hand-coded or generated, it
  needs to be tested.

15
Abusing AP

• No retesting after class graph change. Reusing a
  piece of software (e.g., a strategy) in a new
  context (a new class graph) requires retesting.
  Antidecomposition adequacy rule (Weyuker)
• There exists a program P and a component Q of P
  such that T is adequate for P, T' is the set of
  vectors of values that variables can assume on
  entrance to Q for some t of T and T' is not
  adequate for Q.

16
Abusing AP

• Ignoring Errors() and Diff() output because the
  regenerated program compiles. Uncritical
  acceptance of the analogical transformation done
  by the AP compiler.