A Scheduling Service Oriented Approach for Workflow Scheduling

byConan Fan Li

Supervisor: Dr. Wendy MacCaullCommittee member: Dr. Man LinCommittee member: Dr. Iker Gondra

A SSO approach for workflow scheduling

• Initiatives• AIF project: building decision-support through dynamic

workflow systems.• Workflow engines are not naturally built for scheduling

problems

What is a workflow?• A workflow or a workflow model is a depiction of a

business process composed of a sequence of operations (tasks).

• Tasks are connected in the form of a directed graph to provide an abstraction of the real work for further assessment.

What is a workflow?

What is a workflow?

Why workflow?• Abstraction & visualization• Clarity & consistency• Automation

What is scheduling?• The process of making decisions about the

allocation of resources for a number of tasks to achieve one or more objectives?

• Two main applications

Application of schedulingManufacturing (e.g., a car factory)

Application of schedulingService industry (e.g., Gate Assignments at an Airport)

Basics of Scheduling• A scheduling problem can be described by a triplet

α | β | γ. • α describes the machine environment• β describes the processing characteristics and constraints• γ describes the objective

• The triplet Jm | prec | Cmax describes a job shop scheduling problem with precedence constraints and an objective to minimize the makespan

A Job Shop Example

(0,7) (1,9) (2,21) (3,5) (4,15) (5,30)

M0

M1

-job, processing time, machine, precedence, requirement, schedule, makespan

Workflow Scheduling

• Petri net based scheduling

job machine precedence constraint

Workflow Scheduling

Petri net based scheduling

(0,7) (1,9) (2,21) (3,5) (4,15) (5,30)

M0

M1

job 0

job 2

job 4

M0

M1

job 5

job 3

job 1

The SSO approach• An approach that maps a scheduling problem onto a

workflow model that consists of tasks that provide services for scheduling.

• Proposed scheduling services include:• selection• allocation• push• pop• process

Selection

5 10 15 20 250

(0,7)

(1,9)

(4,15)M0

M1

(0,7) (1,9) (2,21) (3,5) (4,15) (5,30)

M0

M1

Selection

• S'=select(S,c) returns a subset of S. Fore each element e in S', c(e) must be True.

• Eg. if we define o c1(j)= isNotScheduled(j) && isIndependent(j)

o then select(J,c1) returns {J0, J2, J4}

(0,7) (1,9) (2,21) (3,5) (4,15) (5,30)

M0

M1

Allocation

• Given a partial schedule and a number of jobs ready to be scheduled, the allocation service produces the set of successors

• For example, let sch0 be the initial schedule where no job is scheduled. allocate(sch0,{J0,J2,J4}) will generate the following three schedules.

Allocation

• allocate(sch0,{J0,J2,J4})

5 10 15 20 250

(4,15)M0

M1

510

15 20 250

(0,7)M0

M1

510

15 20 250

(2,21)M0

M1

Push & Pop

5 10 15 20 250

(4,15)M0

M1

510

15 20 250

(0,7)M0

M1

510

15 20 250

(2,21)M0

M1

Push

Pop

Process

5 10 15 20 250 30

(0,7)

(1,9)

(4,15)M0

M1

clock=7

futurepast now

slot=16

(0,7) (1,9)(2,21

)(3,5)

(4,15)

(5,30)

M0

M1

Process

(0,7) (1,9)(2,21

)(3,5)

(4,15)

(5,30)

M0

M1

5 10 15 20 250 30

(0,7)

(1,9)

(4,15)M0

M1

clock=16

futurepast now

slot=22

Schedule-flow

select

allocate

process

push

something is selected

nothing is selected

queue is not empty

endstart

pop

Schedule-flow in YAWL

PYSF

PYSF

SSO vs. Classic

SSO vs. Classic

• Size

SSO vs. Classic

• Size

select

allocate

process

push

something is selected

nothing is selected

queue is not empty

endstart

pop

SSO vs. Classic

1:0

SSO vs. Classic

• Performance

SSO vs. Classic

SSO Classic

Time/second 0.22 > 20

Makespan 1094 1100

SSO vs. Classic

2:0