deriving explicit data links in ws-bpel processes

International Conference on Services ComputingSCC 2008 – http://conferences.computer.org/scc/

Deriving Explicit Data Links inWS-BPEL ProcessesWS BPEL Processes

Oliver Kopp, Rania Khalaf, Frank LeymannInstitute of Architecture of Application Systems

[email protected]

Background and Motivation

For splitting BPEL-processes, the dataflow edges have to be knownhave to be known

i.e. the def-use-edges (writer-reader-relation)

31 2

12

01

2

0

14 5

33

03

w2 and w3 are possible writers for r1w1 is a possible writer for r2

Presented by Oliver Kopp Deriving Explicit Data Links in WS-BPEL Processes 2

Weaknesses of existing approaches

No direct support for DPENo direct support for DPEAND-join “optimization” not built in

No support for compound variables


Basic idea

Considering flow onlyNo scope, no loop p , p

O i tiOverapproximationA dataflow-edges too much is better than a gdataflow-edge too less


The function writes

Possible writerswrites : (A [ E)£ V ! 2A £ 2A £ 2A £ Bwrites : (A [ E)£ V ! 2A £ 2A £ 2A £ B

Possible writers Disabled writersInvalid writersInvalid writersMay-be-dead


Writers before and after interpretation of an activity

is split upreturns the result before interpreting anitit

writeswrites

returns the result before interpreting an activitywrites±writes±

returns the result after interpreting an activitywrites²writes²


Initialization

writes±(a; v) Ã (;; ;; ;; false)writes±(a; v) Ã (;; ;; ;; false)

i ( ) (; ; ; f l )i ( ) (; ; ; f l )writes²(a; v) Ã (;; ;; ;; false)writes²(a; v) Ã (;; ;; ;; false)


interpretActivity

Handles writing activitiesinterpretActivity : A£ V £ 2A £ 2A £ 2A £ B ! 2A £ 2A £ 2A £ BinterpretActivity : A£ V £ 2A £ 2A £ 2A £ B ! 2A £ 2A £ 2A £ B

gHandling of joinConditions is taken into account by joinLinks() (see later)If a is no writer: identitiy. Otherwise: If there was a transition condition:

P ibl it di bl dPossible writers are disabledElse

Possible writers get invalidPossible writers get invalidActivity itself may not get disabled or invalid

interpretActivity : (a; v; P;D; I; d) 7!

8><(fag; D [ P n fag; I; false) w(a; v) ^ d

(fag;D; I [ P n fag; false) w(a; v) ^ :dinterpretActivity : (a; v; P;D; I; d) 7!

8><(fag; D [ P n fag; I; false) w(a; v) ^ d

(fag;D; I [ P n fag; false) w(a; v) ^ :d


<>:id :w(a; v)

<>:id :w(a; v)

Step from an activity to a link

Li k h l ti it Th fwrites±(l; v) Ã writes²(V

¡(l); v)writes±(l; v) Ã writes²(V¡(l); v)

Link has only one source activity. Therefore, the result from the source activity can just be t k i ttaken as input

writes²(l; v) Ã (poss±(l; v);writes²(l; v) Ã (poss±(l; v);²( ; ) (p ±( ; );

dis±(l; v);

inv±(l; v);

²( ; ) (p ±( ; );

dis±(l; v);

inv±(l; v);

everything is preserved, existence of tc

±( ; );

mbd±(l; v) _ :alwaysTrue(tc(l)))

±( ; );

mbd±(l; v) _ :alwaysTrue(tc(l)))

y g ppossibly evaluating to false is noted


Step from a link to an activity

writes±(a; v) Ã joinLinks(a; v)writes±(a; v) Ã joinLinks(a; v)

is joining the information of thewrites²(a; v) Ã interpretActivity(a; v;writes±(a; v))writes²(a; v) Ã interpretActivity(a; v;writes±(a; v))

joinLinks(a; v)joinLinks(a; v) is joining the information of the incoming links

h dl i i

j ( ; )j ( ; )

i A i i ( )i A i i ( ) handles one incoming link (which was created by joinLinks)interpretActivity(a; v; : : :)interpretActivity(a; v; : : :)


joinLinks: Possible Writers

joins the information on the incoming linksjoinLinks : (a; v) 7! (P;D; I; d)joinLinks : (a; v) 7! (P;D; I; d)

on the incoming linksAn OR join may revive disabled writersj yIf each incoming link disables a writer, this writer will not revive at this join (i e itwriter will not revive at this join (i.e., it remains disabled)

P =

8>>< [l2E¡(a)

possible(l; v) (jc(a) = AND) _ (jE¡(a)j = 1)[possible(l v) [ disabled(l v) n

\disabled(l v)

P =

8>>< [l2E¡(a)

possible(l; v) (jc(a) = AND) _ (jE¡(a)j = 1)[possible(l v) [ disabled(l v) n

\disabled(l v)

<>>: [l2E¡(a)

possible(l; v) [ disabled(l; v) n\

l2E¡(a)

disabled(l; v) otherwise

<>>: [l2E¡(a)

possible(l; v) [ disabled(l; v) n\

l2E¡(a)


plus: Link may not have a


plus: Link may not have anegative join condition

joinLinks: Disabled Writers

An OR join revives disabled writersjoinLinks : (a; v) 7! (P;D; I; d)joinLinks : (a; v) 7! (P;D; I; d)

An OR-join revives disabled writers.But not these, which are disabled on all paths

D =

8>>< [l2E¡(a)

disabled(l; v) (jc(a) = AND) _ (jE¡(a)j = 1)\D =

8>>< [l2E¡(a)

disabled(l; v) (jc(a) = AND) _ (jE¡(a)j = 1)\D<>>: \

l2E¡(a)


D<>>: \

l2E¡(a)



joinLinks: Invalid Writers

joinLinks : (a; v) 7! (P;D; I; d)joinLinks : (a; v) 7! (P;D; I; d)

All invalid writers remain invalidI =

[l E ( )

invalid²(l; v)I =[

l E ( )

invalid²(l; v)l2E¡(a)l2E¡(a)


joinLinks: May be Dead

8< false alwaystrue(jc(a))8< false alwaystrue(jc(a))

joinLinks : (a; v) 7! (P;D; I; d)joinLinks : (a; v) 7! (P;D; I; d)

Activity a may never be dead even if dead paths may

d Ã

8<: true negations(jc(a))

:[[a; v]]jc:mbd² otherwise

d Ã

8<: true negations(jc(a))

:[[a; v]]jc:mbd² otherwise

Activity a may never be dead, even if dead paths may reach a. For example: There is one path, which is not dead and activity a contains an “OR” join condition. y j

Use the negated value of mbd of each link

mbd²(l1; v) = true; mbd²(l2; v) = fale; jc(a) = l1 _ l2mbd²(l1; v) = true; mbd²(l2; v) = fale; jc(a) = l1 _ l2

:[[a; v]]jc:mbd²:[[a; v]]jc:mbd²

Use the negated value of mbd of each link,Interpret the join condition on it,And use the negated result

:[[a; v]]jc:mbd²= :(:mbd²(l1; v) _ :mbd²(l2; v)) = :(:true _ :false) = :(true) = false:[[a; v]]jc:mbd²= :(:mbd²(l1; v) _ :mbd²(l2; v)) = :(:true _ :false) = :(true) = false


Complex Types

Problem:$v and $v part exist in real BPEL processes$v and $v.part exist in real BPEL processesExample:

w1: write to $v.p1 w2: write to $v.p2

Solution: Build a lattice for each variableEach node of the lattice is called “variable element”

$v

$v.part1 $v.part2


Handling of Complex Types

if a completely writes to ve

if a completely reads vw(a; ve) = truew(a; ve) = true

( )( ) if a completely reads ve

Data link has to be created from w to z,r(a; ve) = truer(a; ve) = true

if w reaches z and z reads a variable element, where parts were changed by w

Start the analysis for each variable elementDL := f(w;z) j z 2A[L; w 2 poss±(z; v

0e); v

0e v ve; r(z; ve) = truegDL := f(w;z) j z 2A[L; w 2 poss±(z; v

0e); v

0e v ve; r(z; ve) = trueg

Sta t t e a a ys s o eac a ab e e e e tOptimization: Iterate at each activity over all variable elements


Loops

is the keyThe current data of writes(l v) has to bett

The current data of writes(l,v) has to be combined with writes(nested(l,v))

A hil ti it d t it t i bl it lfA while activity does not write to a variable itself Terminate if writes(l,v) do not change


Future Work


deriving explicit data links in ws-bpel processes

Technology