Transcript
Jane Doe & Jane Doe
Oct, 2012
BPP 3213 PROJECT ESTIMATION AND SCHEDULING
Lecture 2 Network Scheduling and Precedence Diagram Method (PDM)
Faculty of TechnologyUniversiti Malaysia Pahang
RECAP
Project life cycle
Organization Structure
Challenges
Purpose of this lecture
To better understand:
• brief history of scheduling techniques
• network scheduling and logic diagrams
• the importance of Critical Path Method (CPM)
• the fundamental elements of precedence diagram method (PDM)
Scheduling is for everyoneit is a discipline that is
performed by every person, every day.
Scheduling is an application of special knowledge or judgment of the
mathematical , physical, or engineering sciences to the conception or
implementation of creative work.
The History
Brief History
Gantt Charts / Bar Charts
History Advantage Drawback
Until 1958, the only tool for project scheduling was a bar chart
Henry Gantt had developed a complete notational system showing progress with bar chart, thus they called Gantt charts
Simple to construct and read
difficult to determine the impact of slip on one task on the rest of the project
Brief History (cont’d)
Arrow Diagrams
History Advantage Drawback
Late 1950s and early 1960s, two methods of scheduling were developed to capture the sequential and parallel relationships among project activities
An arrow diagram help the team understand the interdependencies of the tasks
Tend to be too complicated for some teams
Brief History (cont’d)
Critical Path Method (CPM)History Advantages Drawbacks
Developed by Du Pont in 1957
Initially to address the challenge of shutting down chemical plants for maintenance and restarting it again once maintenance completed
Utilizes the planner’s knowledge, experience, and instincts in a logical way
Graphical view of the project
Predicts the time required for the project
Shows which activities are critical to maintain the schedule and which are not
CPM can be complicated, and complexity increases for larger projects
Does not handling the scheduling of personnel and resource allocation
Not always clear and need to be calculated carefully
Estimating activity completion times can be difficult
Brief History (cont’d)
Program Evaluation and Review Technique (PERT)
History Advantages Drawbacks
Developed by US Navy and Booze, Allen and Hamilton at late 1950’s
It allows for randomness in activity completion times
Has potential of reducing both time and cost required to complete the project
Complicated chart
Prediction inaccuracies
Brief History (cont’d)
Purpose of a Schedule
Purpose of Schedule
• Schedules are tool to :
Communicate time plan
Assess time plan
Purpose of Schedule (cont’d)
Benefits:- Identify the timeframe- Identify the resource requirement- identify the key milestones- Identify the key stakeholder engagement points- Assess impact of resource constraints- Determine your commitment and obstacles
Schedule Development Process
Resource capacity
Resource capability
Estimates - times
Network-logic
Scheduling Project Schedule
Example Gantt Chart
Logic Diagram & Networks
Your New Tool•Defacto standard for scheduling software in construction industry has been Primavera Project Planner aka P3
•In 2000, P3 has improved for the use by manufacturing and IT industries
Your New Tool (cont’d)
•Major differences that distinguish one software system from another are
• Ease of input
• Ease and variety of means of reporting output
• Features that permit the user to get around some of the limitation of the math upon which CPM is founded to more perfectly model the real world
Logic Diagrams and Networks
• Effective project plan – address equally the parameters and activity logic
• Illustrate the inductive and deductive reasoning to achieve objectives within time given
• Constructed similarly to bar charts – supposing nothing will go wrong
• Normally accompanied by detailed questions/checklist
The Logic of the Logic Diagrams
• backbone of traditional implementation of CPM is graphical model of a project
•Basic component is the arrow
•Each arrow represents one activity in a project
start finishactivity
The Critical Path
The Critical Path • The longest path throughout a project network
• Has no slack (or float) therefore all activities on the critical path must be completed as scheduled
• End date will begin to slip – one day for each day a critical activity is delayed
The Critical Path (cont’d)
• Originally, the critical path considered only logical dependencies between terminal elements
•Since then, it has been expanded to allow for the inclusion of resources related to each activity , through processes called activity-based resource assignments and resource leveling
What is CPM really?
The Critical Path (cont’d)
• Also known as Critical Path Analysis (CPA) – is a mathematically base algorithm for scheduling a set of project activities
• An important tool for effective project management
• Commonly used with all forms of projects including construction, software development, research projects, product development, engineering, and plant maintenance among others
The Critical Path (cont’d)
• Essentially, to construct a model for a project, we need:
WBS Time (duration) Dependencies
Terms you have to get used to...
• Event: equivalent to a milestone – indicate the start and finish dates
• Activity: element of work that must be accomplished
• Duration: total time required
• Effort: amount of work actually performed within the duration
Calender Scheduling• Calendar unit: - Time measurement for project schedule- The smallest unit of time- In hours, days, or weeks, years, months, shifts, even in minutes
• Take into account for issues such as:- For non-working time (weekend, holidays)- Resource constraint- Change risk- Cash flow- Logistics
Precedence Diagram Method (PDM)
• Visual representation technique• Depicts the activities involved in a project• Also known as Project Network Diagrams
• PDM helps:- Communicate - Identify missing activities- Identify critical activities- Create project schedule
Precedence Diagram Method (PDM) (cont’d)
•Types of Dependencies:
- Finish to Start (FS) : the predecessor must be completed before the successor can start
Predecessor10 days
Successor5 days
FS
Start Day: 1Finish Day: 10
Start Day: 10 Finish Day: Start Day + 5
•Types of Dependencies:
- Start to Start (SS) : the successor can start at the earliest after the start of its immediate predecessor
Precedence Diagram Method (PDM) (cont’d)
Predecessor10 days
Successor5 days
SS
Start Day: 1Finish Day: 10
Start Day: 1Finish Day: 5 days after start day
•Types of Dependencies:
-Finish-Finish (FF): the successor will finish at the latest after its predecessor finished
Precedence Diagram Method (PDM) (cont’d)
Predecessor10 days
Successor5 days
FF
Start Day: 1Finish Day: 10
Finish Day: 10Start Day: 5 days before finish day
•Types of Dependencies:
-Start-Finish (SF) : the successor can finish only after the predecessor has started
Predecessor10 days
Successor 5 days
SF
Precedence Diagram Method (PDM) (cont’d)
Precedence Diagram Method (PDM) (cont’d)Multiple PDM Relationships:• Two PDM dependencies/relationships can be used together – combination• Having both SS and FF relationships in one activity
15Activity A
15Activity B
SS =5
FF=10
• B must be finished not later than 10 days after A is finished and starts after 5 days A started i.e. starts at day 10
Precedence Diagram Method (PDM) (cont’d)
Lag Time:
• It’s a technique• Occurs when you add time to the start or finish of predecessor task• Causes a gap in timing• E.g.: FS dependency with 5 days lag = the successor cannot start until 5 days the predecessor has finished
Precedence Diagram Method (PDM) (cont’d)
Lead Time:
• It’s also a technique• Created when you subtract time from the start or finish of predecessor task• Causes overlap between two tasks• Allow acceleration of the successor activity• E.g.: FS dependency with 5 days lead= the successor can start 5 days before the predecessor has finished
Level of Detail• Should never have too little nor too much detail
• Logical structure with appropriate level of detail is the key to tracking throughout the project
• Contents information required to manage the project – only that information
• Rule of thumb:- 80 hour rule- if it make sense
Conventional Assumptions
• Activity duration – scheduling done based on expected or most likely time duration for each activity
• Contingency allowance for activity duration
• Availability of resources
• Schedules to have low cost or ideally lowest cost
Summary
•Network scheduling and PDM are techniques to assist PM in scheduling – translating project brief into time schedule
Questions??? He who ask is a fool for five minutes, but he who
does not ask is a fool forever.
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