0.3 Cost Engineering and Scheduling Terminology per RP 10S-90

0.3 Cost Engineering and Scheduling Terminology per RP 10S-90

AACE RP 10S-90, Cost Engineering Terminology, provides a common vocabulary across cost engineering and project controls. Consistent terms make schedules, estimates, reports, and analyses easier to review. When a project contract or specification defines a term differently, the governing project definition must also be considered.

Data date

The data date or status date is the point separating statused performance from forecast work. Actual starts, actual finishes, and measured progress belong on the historical side according to the update rules; incomplete remaining work is forecast from the data date forward. Exact treatment of time-of-day, out-of-sequence work, and actual dates depends on the software and specification, so reviewers should confirm settings.

Activity, milestone, and work package

An activity is a definable element of work represented with duration, calendar, status, and relationships. It may carry resources, cost, coding, and responsibility. A milestone is a zero-duration event such as an approval, delivery, phase start, turnover, or completion.

A work package is a control element within a scope breakdown. It can contain several schedule activities and may be the level at which scope, budget, and responsibility are managed. Do not assume that every work package should be one long activity; decompose it enough to model interfaces and objective progress.

Early and late dates

The forward pass calculates early dates from project start, logic, durations, and calendars. The backward pass calculates late dates from a finish target or other late-date basis. Under a zero-based convention:

$EF = ES + D$

$LS = LF - D$

Under inclusive day numbering, the formulas adjust by one. State the convention before comparing hand calculations with software dates.

Total and free float

Under compatible assumptions:

$TF = LS - ES = LF - EF$

Total float describes flexibility relative to the modeled late date. It is commonly shared along a path, so delay to an upstream activity can reduce the flexibility available downstream.

For a simple zero-lag FS relationship:

$FF = ES_{successor} - EF_{activity}$

Free float is the movement possible without delaying the immediate successor’s early date. Other relationship types, lags, successors, and calendars require endpoint-aware calculation. Neither metric assigns contractual ownership. Float use and ownership depend on the contract and applicable law.

Critical path and driving relationship

The critical path is the continuous sequence that controls the relevant completion or milestone under the schedule model. In a simple unconstrained network it often has zero float. With an earlier imposed finish it may have negative float; with a later target it may have positive float. Trace the longest or driving path and reconcile it with the lowest-float result rather than filtering only for zero.

A driving relationship is an incoming relationship that directly determines an activity endpoint’s calculated early date. An activity can have several predecessors while only one or several ties are driving at a particular calculation. Path drivers can change after status, duration, logic, calendar, or constraint changes.

Baseline, current schedule, and forecast

The baseline is an approved reference for comparison under the project’s governance. The current schedule contains validated status and the current model of remaining work. The forecast is the present estimate of future dates. A baseline revision requires the authority and process defined by the project; it is not automatically permitted or prohibited by terminology guidance.

Schedule variance and earned value

In earned value management:

$SV = EV - PV$

This schedule variance is expressed in currency or another value unit, not calendar time. Earned Schedule uses time-based measures such as SV(t) = ES − AT. Neither aggregate measure replaces CPM milestone and path analysis.

Fragnet

A fragnet is a fragmentary network of activities and relationships representing a change, event, or defined piece of analysis. It can support planning or time-impact analysis, but the appropriate schedule version, tie-ins, status treatment, and contractual use depend on purpose and governing requirements.

Use terminology precisely, state conventions, and disclose project-specific definitions. That discipline prevents a technical discussion about float or variance from silently becoming an unsupported contract conclusion.

Applied review: state the reference behind the term

When using a term in a report, identify the milestone, calendar, data date, and calculation basis that give it meaning. “Five days of float” is incomplete unless the reader knows which finish target and schedule version produced the value. “Behind schedule” may refer to earned value, milestone variance, or a delayed controlling path; name the measure.

If contract language uses a defined term such as completion, excusable delay, or approved baseline, quote or cite that definition separately from the technical schedule vocabulary. This keeps a sound CPM calculation from being presented as a legal conclusion it cannot establish by itself.