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Topic 22

Scheduling Systems Overview

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Implementation

Scheduling modelsSolution methods

Advanced Planning and Scheduling (APS) systemEnterprise-wide information system (ERP)

System Design

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Overview

Context for scheduling systems Enterprise Resource Planning Levels of planning

Elements of scheduling systems Database Schedule generator User interface

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ERP Systems

Enterprise Resource Planning (ERP) system Enterprise wide information system

Single master database

Origins in manufacturingComputer Integrated Manufacturing (CIM)

Materials Requirement Planning (MRP)

Ties with back office functionsAccounting, marketing, manufacturing, etc

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ERP Systems

Database

Materials RequirementPlanning (MRP)

Marketingand Sales

ProductDefinition

Scheduling

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Advanced Planning and Scheduling (APS) Systems

Database Management

Automatic Schedule Generator

Schedule Editor Performance Evaluation

Graphical User Interface (GUI)

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Generic or Application Specific

Generic May require a great deal of customization Relatively inexpensive but slower Support from software vendor

Applications specific Large problems/databases Specialized scheduling environment In-house maintenance

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Topic 23

Planning Levels

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Scope of Scheduling

Scheduling: determining how to use resources in the optimal manner

Many levels abstraction of resources

e.g., plants, work stations, machines, tools

time horizon

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Levels of Scheduling

Long-range planning 2-5

years

Middle-range planning 1-2 years

Short-range planning 3-6 months

Scheduling 2-6 weeks

Reactive scheduling 1-3 days

ERP

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Industry Example: Oracle

Source: http://www.oracle.com/applications/B2B/Planning/index.html?solution.html

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Long-Range Planning

Problems: Plant expansion Plant layout Plant design

Most important: forecasting issuesLot sizing models used but not

very successfully (see later)Need stochastic models

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Middle-Range Planning

Problems: Production smoothing Logistics

Scheduling successful at this level

Forecasting remains difficult

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Short-Range Planning

Problems: Material Requirements Planning (MRP) Setting due dates and release times

MRP Starts with mid-range production schedule Known orders & statistical predictions Obtain master schedule Assumes infinite capacity and whole day buckets

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Scheduling

Problems:

Job shop routing

Assembly line balancing

Process batch sizing

Given due dates, raw material release time

Typically develop 6 week schedule once a

week

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Reactive Scheduling

Problems Hot jobs Down machines Late material

Make correctionsHuman elementInteractive scheduling and

reoptimization

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Hierarchy

Traditional Top-down Long-range planning scheduling

New development ERP allows greater integration More interaction

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ERP System Interactions

Advanced Planning and Scheduling Scheduling Capacity management

ASPSystem

Bill of MaterialsRoutings

Production ScheduleDue Dates

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ERP Systems (example)

ASPSystem

MRPSystem

What if ?

- high priority order- schedule overtime

Complete integration

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Topic 24

Data & Databases

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Databases

Custom or commercial database system Microsoft SQL Server, Oracle, Sybase Structured Query Language (SQL)

Basic functions Editing Sorting Searching

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Types of Data

Static Data Number of machines Layout Due date Release date

Dynamic Data Starting time Completion time Sequence of jobs Tardiness

Independent of the schedule

Depend on the schedule

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Job Data

ID Name Type Quantity Priority Ready Due

2 IBM 4 160 2 10 200

Job Data Type

Job Instance

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Job Object

Job ID

NameType

QuantityPriorityReadyDue

createcopydelete

display

ID = 2

Name = IBMType = 4

Quantity = 160Priority = 2Ready = 10Due =200

createcopydelete

display

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General Enterprise Data

Plant layout Work centers and machines

Resource calendar Shift schedules, holidays, maintenance

schedulesRouting table

Which machines can be used, precedence constraints

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Topic 25

Schedule Generation

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Schedule Generation

Algorithm Approach(This is what we have been doing.)

Knowledge-Based Approach

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Algorithm Approach

Mathematical formulation decision variables objectives constraints

Three phases:

E x a m p le : jjTw||1

P r e p r o c e s s in g C a lc u la t e t ig h t n e s s o fd e a d l in e s

A lg o r it h m A p p ly t h e A T C r u le

P o s t p r o c e s s in g I m p r o v e s e q u e n c eu s in g T a b u s e a r c h

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Knowledge-Based Approach

Underlying problem structures Feasible/preferred solution

Schedulerknowledgeof system

Rules andobjects

Data MiningHistoricaldata

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Algorithm Approach Characteristics

Is mathematical formulation possible?

Rule of thumb: should be applied for systems with Large number of jobs Minimum randomness Frequent real-time optimization Consistent general rules

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Knowledge-Based Approach Characteristics

Any feasible schedule sufficesMay be easier to adapt to system

changes

Hybrid of both approaches? Recent convergence Unusual to find a system that does not

have some elements of each

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Topic 26

User Interfaces

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User Interfaces

Very important part of the systemMay determine if system is used or

notSeveral different types

Gantt chart Dispatch list Capacity bucket list Throughput diagram

Graphical interfaces

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Gantt Chart

Most popularGood overview of schedules

tardy jobs machine utilization

Disadvantages limited when many jobs/machines

“Drag-and-drop” cascading/propagation effect,

reoptimization

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Dispatch List

Ordered list of jobs starting time machine processing time due date, etc.

Unlimited number of jobsOverview with respect to time

limited

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Capacity Buckets

Partition time into slots or bucketsProcessing capacity of each machine

known

Percentage of capacity used in each bucket

Medium to long-range planning

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Throughput Diagram

Total orders received produced shipped

Over timeInformation on:

Machine utilization WIP

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Topic 27

Internet Scheduling

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E-Scheduling

Information access systems Electronic Data Interchange (EDI)

Information coordination systems Internet GUI

Information processing systems Actual scheduling done over the

InternetInternet scheduling systems

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Information Processing Systems

Application Service Providers (ASP) Host enterprise software Clients access via the Internet Pay on per-use basis Advantages:

Low initial costSystem support from ASPReaches midsize to smaller enterprises

Hot for ERP, etc.

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Possible Directions

Standardization

Customization

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Internet Scheduling

Network structure Scheduling server(s) Local clients

Advantages Local clients can support GUIs Server/clients can share data

management Servers can jointly (distributed) solve

large scheduling problems

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Internet System Design

Server

ServerDatabase

ClientDatabase

Client

Schedule Information Process Information

Inte

rnet

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Division of Labor

Server

ServerDatabase

ClientDatabase

Client

Inte

rnet

Formulate problem(Select algorithm)(Run algorithm)Display schedule

Select (suggest) algorithmRun algorithmCreate schedule display

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New Algorithm Generation

Server MainAlgorithm

Library

LocalAlgorithm

Library Client

Inte

rnet

First Algorithm AlgorithmGenerator

Composite Algorithm

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ToolsExisting Internet support

Markup Languages: HTML, XML, DHTML Java Applets Scripting: JavaScript, VBScript, etc. Active Server Pages (ASP)

Browsers Netscape Internet Explorer (IE) Compatibility

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Applying the Tools

Server

ServerDatabase

ClientDatabase

Client

Inte

rnet

HTML - XML for schedulingJavaScript - Define problemJava Applets - Display results

ASPVBScript - Select algorithmJava (other) - Run algorithm

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Discussion

Future of all enterprise softwareAdvantages

Higher speed at lower costChallenges

Ownership of data/systems Customization versus standardization Security Effective designs? Collaboration?

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Future of Scheduling

System developmentE-Scheduling!Integration with other functionAvailability of data (mining?)Computing power

Increased importance of scheduling