activity
The smallest amount of work defined in a critical path method
schedule. Typically an activity is defined as a single type of work
completed by a single crew in one specific area of work. Non-work
activities are included in a schedule when they significantly constrain
production activities.
actual cost of work performed
(also ACWP) The total cost incurred within a given time period.
A cumulative ACWP reflects the total costs incurred since the start of
the project.
actual finish date
The date that an activity finished. See also the section on cost vs. time
completion and out-of-sequence progress.
actual start date
The date that an activity actually began.
arrow diagramming
Arrow Diagramming, or "activity-on-the-arrow"
scheduling, is a method of CPM scheduling that shows an
activity as an arrow. Sequence between activities is
identified by the activities that merge at the head or tail
of the arrow. Combining activity duration and sequence on the
same arrow results in the need for two types of "dummy"
logic relationships. These dummy relationships are the
numbering dummy and the logic dummy.
backward pass
The backward pass is the second part of the CPM calculation
procedure. The backward pass answers the question,
"How late can I start any activity without delaying
the project?"
baseline schedule
A schedule that has been agreed upon by all parties to be the basis upon
which to calculate time and earnings progress. The originally approved
schedule is the first baseline schedule. New baselines will
typically be establised following agreements of cost and time as issued
in construction contract modifications.
budgeted cost of work performed
(also BCWS) The estimated costs for work that has been actually accopmlished.
This value may be compared directly to the actual cost of
work performed to determine if the project is meeting contractor direct cost goals.
Some text link 'cost' and 'earned value', this is not correct since
earned value calculations include overheads and profits not included in
direct construction costs.
budgeted cost of work scheduled
(also BCWS) The expected cost that should be incurred at a given time
in the future, if the project proceeds as scheduled.
Some text link 'cost' and 'earned value', this is not correct since
earned value calculations include overheads and profits not included in
direct construction costs.
cost loading
Adding the budgeted cost, actual cost, and earned value to the schedule
can signficantly improve a project managers ability to detect cost
overruns as the project progresses. Cost-Time Tradeoff analysis and
cash flow analysis may also be accomplished if a schedule is loaded with
the direct costs of each activity. Also see value loading
cost variance
(also CV) The difference between the budgted cost of work performed and
the actual cost of work performed. This can be used to calculate the accuracy of the
original estimates and/or the efficience of the construction work.
Some texts describe cost variance as related to 'earned values' to be
precise about such language this is not correct since direct project costs,
from a contractors point of view, does not include overheads and profit
that is included in 'earned value' calculations.
critical path
The critical path is that set of activities from the
start of the project through to the end, that have the minimum
total float. This total float is a shared property of all
activities on the critical path.
critical path method (CPM)
The Critical Path Method is a project model that reflects work
to be accomplished and shows the sequence of work. CPM
Calculations assist the project manager to identify how
soon the project can be completed, and identify those critical set of
activities that, if delayed, also delay the entire project. In CPM,
“work” is defined as “activities.” “Sequence” is defined differently
in each of the two types of CPM scheduling, Arrow Diagramming and
Precedence Diagramming
direct cost
The amount that the contactor must pay for labor, materials,
and equipment to complete a specific production activity.
Direct costs must not include the cost of project trailers,
home office staff, transportation, permits and other indirect
costs.
earned value
The amount that the contactor must charge the owner to recoup
direct costs, indirect costs, and profit. In the CPMtutor I
have tried to be very clear about the difference between the "costs"
incurrec by construction contractors and the "costs" (i.e. "earned
value") incurred by the project owner. Great care must be taken
when discussing "costs" with owners since they will typically be
talking about "earnings" and not the contractor's actual cost.
finish date
The Finish Date is that date that governs the completion of
a given activity. There are at least two Finish Dates for
every activity in a CPM network. The first Finish Date is the
"Early Finish". Early Finish is the earliest date
on which the activity can finish. The second Finish Date is
the "Late Finish." Late Finish is the latest date
on which the activity can finish without delaying the overall
project.
finish-to-finish
Finish-to-Finish is one of the ways to model of the underlying
physical constraints of work to be accomplished in CPM.
Identifying the sequence between two activities as a
Finish-to-Finish sequence indicates that the prior activity must
end prior to the end of the following activity.
Finish-to-Finish is typically found in Precedence Diagrams
only since the modeling Finish-to-Finish using the Arrow
Diagram requires the addition of partially complete activities
and, often, logical dummies. In general, two activities
with a Finish-to-Finish sequence will also have a complementary
Start-to-Start sequence.
finish-to-start
Finish-to-Start is one of the ways to model of the underlying
physical constraints of work to be accomplished in CPM.
Identifying the sequence between two activities as a
Finish-to-Start sequence indicates that the prior activity must be
completed prior to the start of the following activity.
Finish-to-Start is the most commonly used sequence in CPM.
Finish-to-Start sequence is easily modeled in both Arrow and
Precedence Diagramming.
float
Float or Slack typically refers to the CPM value of "Total
Float." Total float is the time difference between the
earliest possible start of an activity, derived from the
forward pass, and the latest possible start of an activity,
derived from the backward pass. Float may have one of three
types of values. A positive float indicates that the activity
may be delayed without delaying the project. A zero float
indicates that the activity cannot be delayed without delaying
the project. A negative float value indicates that the project
is behind schedule and the negative time value indicates the
amount of that delay. Float is a property of a series of
tasks within a network path. As a result changes to the start
time or duration of any of the activities in that path will result
in a corresponding change in total float to all activities in the
path.
forward pass
The forward pass is the first part of the CPM calculation
procedure. The forward pass answers the question "how
early can I complete this project?"
indirect cost
The costs incurred by the contractor to be able to perform the
actual construction work. Indirect costs include, but are not
limited to, the cost of project trailers, computers, telephones,
home office staff, transportation, permits, etc... Allocation
of indirect costs to determine an appropriate value to charge the
owner for the task ('earned value') by adding a percentage increase
to each product tasks.
lag
When two activities have a Finish-to-Finish sequence, there
may be time delay between the time when the first activity
ends and the second activity ends. This time delay on the
Finish-to-Finish sequence is called "Lag" time.
lead
When two activities have a Start-to-Start sequence, there may
be time delay between the time when the first activity starts
and the second activity begins. This time delay on the
Start-to-Start sequence is called "lead" time
resource leveling
See unlimited resource leveling
limited resource allocation
When there are insufficent resources to complete your project,
then you should conduct the limited resource allocation analysis.
This procedure can be used to determine when the project might be
finished under different resource constraints.
milestone
A milestone is a date that is included in a schedule to
override standard CPM scheduling calculations. There are
several different types of milestone dates. Due to the
differences in calculations related to these dates, and the
associated difficultly of the project team to clearly discuss
the results of such calculations, only two dates that
should be typically used. The first of these dates impacts
the earliest that an activity can start. An example of such
a milestone would be the project start date. The second of these
dates impacts the latest that an activity can finish. An
example of such a milestone is the project end date.
precedence diagramming
Precedence Diagramming, or "activity-on-the-node"
scheduling, is a method of CPM scheduling that shows an
activity as a box. The sequence among activities is shown
as arrows. Separating sequence from the definition of the
activity eliminates the need for "dummy" logic as
and unique as is required in the Arrow Diagramming Method.
project
A project is any undertaking with a defined start and end.
Projects have defined objectives that when completed,
demonstrate the completion of the project. Most projects
are required to be completed with limited time, labor,
equipment, funds, and other resources.
project management
Project management is art and science of using limited time,
labor, equipment, funding, and other resources to complete a
project to the satisfaction of all project stakeholders.
Stakeholder satisfaction may be defined by a variety of
tangible and intangible goals. Of tangible concern of project
managers is completing a project within budget and on-schedule.
Somewhat less tangible concerns of project managers include
management of project scope changes and issues of quality control.
schedule variance
(or SV). The difference beween the actual cost of work performed and
the budgeted cost of work scheduled. This shows if the project is
ahead of schedule, or behind schedule, with respect to cost.
Some text link 'cost' and 'earned value', this is not correct since
earned value calculations include overheads and profits not included in
direct construction costs.
sequence
In CPM the order, or precedence, of activities is typically
identified in a table that lists each activity and the
activities that precede that activity.
start date
The Start Date is that date that governs the starting of a
given activity. There are at least two Start Dates for every
activity in a CPM network. The first Start Date is the
"Early Start". Early Start is the earliest date on
which the activity can start given it’s prior activities.
The second Start Date is the "Late Start." Late Start
is the latest date on which the activity can start without
delaying the overall project.
start-to-start
Start-to-Start is one of the ways to model of the underlying
physical constraints of work to be accomplished in CPM.
Identifying the sequence between two activities as a
Start-to-Start sequence indicates that the prior activity
must begin prior to the start of the following activity.
Start-to-Start is typically found in Precedence Diagrams
only since the modeling Start-to-Start using the Arrow
Diagram requires the addition of partially complete activities
and, often, logical dummies. In general, two activities
with a Start-to-Start sequence will also have a
complementary Finish-to-Finish sequence.
time-cost tradeoff
Time-Cost Tradeoff is the procedure used to evaluate the impact
of direct versus indirect costs. In many projects increasing
the cost of some activities on the critical path, by increasing
resources or working additional shifts, could result in an overall
decrease of project cost. This technique should always be used when
there are completion incentives. The technique should also be used
when there are liquidated damages on the project.
unlimited resource leveling
When you have enough resources (typically labor) to complete the project
but the levels of required resources vary over time, you should consider
performing the unlimited resource leveling analysis. This analysis
technique will reduce the churn of workers on your site, and will promote
higher quality work and improved productivity.
value loading
Owner requirements for "cost-loaded" schedules are actually
requirements to assign the proportional "bugeted earned value."
As the work is completed, the owner and contractor agree on the
fiscal percent for each activity and thus determine the payment
owed to the contractor. Also see cost loading
work breadkown structure
(or WBS) Work breakdown structure defines the way in which you will
need to decompose actual work into the models of the work activities
in the CPM schedule. Typically you should have multiple types of classifications
to develop a work breakdown schedule. For example crew type and work area
are two of the most critical categories you can use to create a WBS.
CPMtutor also recommends use of activity type (non-work vs production acivity)
and bid item codes as the for components of any useful WBS.