Deriving Explicit Data Links in WSBPEL Processes

1
Deriving Explicit Data Links in WS-BPEL Processes

• Report Kuang-Shun Liao

2
Reference

• O. Kopp, R. Khalaf, and F. Leymann, Deriving
  Explicit Data Links in WS-BPEL Processes, IEEE
  International Conference on Services Computing
  (SCC'08), July 2008, pp.367-376.

3
Outline

• Challenges of Dead Path Elimination (DPE)
• The Algorithm
• Explicit Data Links
• Analysis Result for the Example Process
• Conclusion

4
Challenges of Dead Path Elimination (DPE)1/3

• wx activity writing to variable x
• rx activity reading from variable x
• a activity not reading or writing
• jc join condition
• tc link with explicit transition condition
• l link with default transition condition
  true

5
Challenges of Dead Path Elimination (DPE)2/3

• Case 1
• tc1 false
• jc1 logical AND over the status of all incoming
  links

dead
AND
false
true
false
dead
false
true
6
Challenges of Dead Path Elimination (DPE)3/3

• Case 2
• tc1 false
• jc1 logical OR over the status of all incoming
  links

dead
OR
false
true
false
dead
true
true
7
The Algorithm

• Notations Used in Algorithm
• Handling Complex Type
• Static Analysis
• Store the State of a Writing Activity
• Analysis of a Given BPEL Process
• Handling of an Activity
• Handling Incoming Links
• Handling a Basic Activity
• Handling a Flow Activity
• Handling a Link

8
Notations Used in Algorithm1/3

• Abasic
• The set of all basic activities
• process
• The process element
• Aflow
• The set of all flow activities
• A
• The set of all activities
• A Abasic ? process ? Aflow
• C
• Set of all Boolean conditions
• pi(t)
• Returns the projection to the ith component of a
  tuple t

• L
• All control links in flow activities
• LR ? A L A
• The control link relation
• P(S)
• Denotes the power set of a set S
• Lin A ? P(L)
• Returns the set of all incoming links of an
  activity
• Lout A ?P(L)
• Returns the set of all outgoing links of an
  activity

9
Notations Used in Algorithm2/3

• jc A ? C ? ?
• Returns the join condition of the given activity
• ? denotes an undefined join condition
  defaulting to the logical OR of all incoming
  links
• HR ? A A
• The hierarchy relation denoting the nesting of
  activities
• Let h (p, a) ? HR. Then p is a parent of a
• children A ?P(A)
• Returns the set of all children of the given
  activity with respect to HR

• descendants A ? P(A)
• Returns the set of all transitive children of the
  given activity with respect to HR
• V
• Set of all variables including the variable
  implicitly declared at fault handlers
• QV
• Set of all queries for accessing locations in
  variables
• If the whole variable is accessed, the query is
  empty (e)

10
Notations Used in Algorithm3/3

• EQV ? V QV
• The set of tuples of a variable v and a (valid)
  query q on v
• ? EQV
• The set of variable elements written by
  activities
• w A EQV ? B
• Returns true iff the given activity completely
  changes the given variable element and not only
  parts of it

• r A ?L EQV ? B
• Returns true iff the given activity or link
  completely reads the given variable element

11
Handling Complex Type

• The function returning the set of possible
  writers for a given activity or link and variable
  element during program execution
• An activity is contained in poss? if it
  completely writes to ve

12
Static Analysis

• Bernstein Criterion
• There may be no writes happening in parallel to
  reads on the same variable
• States of a writing activity
• possible writer
• If the data written by writing activity w can
  reach activity a
• disabled writer
• If it is overwritten by a subsequent writer
• invalid writer
• A writer can also be disabled completely and thus
  become invalid

13
Store the State of a Writing Activity1/2

• The current state of the writes to the given
  variable element is assigned to every link and
  activity
• returns the current states of the writes after
  the activity or the link has been interpreted

14
Store the State of a Writing Activity2/2

• Returns the activities which are possible writes
  to the variable element ve at position x in the
  BPEL process
• x can be an activity or a link
• Returns the activities which were overwritten by
  preceding writes from a path leading from the
  root to position x
• Returns true iff x may be not executed due to DPE
  on a path from any directly preceding writer (or
  from the root node if there is no directly
  preceding writer) to x

15
Algorithm 1 Analysis of a Given BPEL Process
16
Algorithm 2 Handling of an Activity1/3
17
Algorithm 2 Handling of an Activity2/3
18
Algorithm 2 Handling of an Activity3/3
19
Handling Incoming Links

• Set P of Possible Writers
• Algorithm 3 - Determining the Set P of Possible
  Writers
• Set D of Disabled Writers
• Algorithm 4 - Determining the set D of disabled
  writers
• State Dead (d) of an Activity
• Algorithm 5 - Determining whether an activity may
  be dead

20
Algorithm 3 Determining the Set P of Possible
Writers
21
Algorithm 4 Determining the Set D of Disabled
Writers
22
Algorithm 5 Determining whether an activity
may be dead

• It takes the negated value of mbd(l, ve) as the
  current status of each link l in the join
  condition of the given activity a and evaluates
  the join condition
• ????????join condition??,?????not,??d (may be
  dead)??

23
Process Illustrating
false
false
false
true
true
true
true
false
false
!(!true OR !false) gt !true gt false
!(!true AND !false) gt !false gt true
mbd(x, ve)
24
Algorithm 6 Handling a Basic Activity
25
Algorithm 7 Handling a Flow Activity
a
l
a
26
Algorithm 8 Handling a Link
a
l
a
27
Explicit Data Links

• The set of all data links in the given BPEL
  process
• w is an activity writing data
• z is an activity or a link possibly reading the
  data written by w

28
Analysis Result for the Example Process
AND
29
Conclusion

• ???????WS-BPEL????DPE???,????????????(write)
  ???(read)?????????(activity)???(link),????????,???
  ?????WS-BPEL?????
• ????????flow activity??structure
  activity????,????????????????????WS-BPEL?????
• ??,??????transition condition ?join
  condition?????????,???????condition?????