ems:Scenario

Domain entities: ems:Project, ems:Scenario, ems:Estimate, ems:Baseline, ems:Measurement

Description

An ems:Scenario is an information resource that describes a project execution scenario. A scenario is one possible way of running a project.

A scenario contains a set of assumptions about scope, resources, productivity, quality, and other metrics. Each assumption may be either a single measure, a fact table, or a work breakdown structure. Since assumptions involve quantities that may not be know precisely, they are described using probability distributions.

While planning a project, it is useful to consider several alternate scenarios and compare their cost-benefit-risk trade-offs. For example, one scenario might be to reduce the requested scope to fit a given schedule, with a given staffing limit. Another scenario might be to deliver the complete requested scope as soon as possible using as much staff as needed.

A manager might define the scenarios to be evaluated. However, if an estimator determines that none of the scenarios are viable, he might define alternate viable scenarios. Scenarios might be defined at the start of the project, or at any time during the course of the project when corrective action is required. Scenarios are the inputs to estimates.

A manager adopts one scenario for the project by creating a new baseline that includes the scenario and its estimates.

Properties

An ems:Scenario resource contains the Standard Properties and the following properties:

dcterms:identifier

ems:scenarioList

See Domain Entities, ems:{entity}List.

ems:project

This property is a link to the ems:Project resource that this scenario applies to. Its value MUST be specified on creation and it SHOULD NOT normally be changed after that, other than to immediately correct an error since this change could invalidate any estimates that were previously based on the scenario.

The referenced resource SHOULD belong to the same service as this result. This specification only defines behavior for when the referenced resource belongs to the same service as this resource. See Distributed Computing for more information.

ems:extendsScenario

A scenario MAY extend another scenario, refered to as the base scenario, by adding new assumptions or refining assumptions present in the base scenario. All assumptions contained in this scenario override any corresponding assumptions in the base scenario.

We refer to the base scenario as the parent of this scenario. An ancestor of a scenario is either its parent or an ancestor of its parent.

In practice, an estimator may extend a given base scenario in order to record additional assumptions made in the process of estimation. The resulting estimate should refer to this extended scenario instead of the base scenario.

This optional property links to an ems:Scenario resource that this scenario extends. Its value, if present, MUST be specified on creation and it SHOULD NOT normally be changed after that, other than to immediately correct an error since this change could invalidate any estimates that were previously based on the scenario.

The referenced resource SHOULD belong to the same service as this resource. This specification only defines behavior for when the referenced resource belongs to the same service as this resource. See Distributed Computing for more information.

If this property is present then the ems:project resource MUST have the same value as the ems:project property of the base scenario.

Note that an ems:Estmate resource MAY refer to an ems:Scenario resource that extends another ems:Scenario resource. If any ancestor scenario is modified after the estimate is created, then is may no longer be valid. The service MAY prevent scenarios from being modified after an estimate uses it either directly or indirectly using access control and policy enforcement mechanisms. The service SHOULD also maintain revision histories to the revisions in effect when the estimate was created can be determined.

ems:isActive

This boolean property indicates whether the scenario is under active consideration as a potential way of running the project. A true value indicates to estimators that they should provide estimates for this scenario when requested. When a scenario has been rejected, this property should be set to false to avoid further estimation work.

After negatively evaluating a scenario, a manager should set this value to false to indicate that is no longer under active consideration as a way to run the project.

ems:assumes

This property gives an assumption for this scenario. A scenario may have zero or more assumptions. The object of this property is an inline ems:MeasureDistribution resource.

An assumption is any condition or constraint that must be obeyed in the scenario, e.g. schedule, staffing, scope. Assumptions often involve imprecisely known quantities such as productivity or size. The uncertainty in assumptions is expressed by giving a probability distribution for the assumed quantities.

ems:assumesTable

Like ems:assumes, except that the object of this property is an inline ems:FactDistributionTable resource.

ems:assumesWbs

Like ems:assumes, except that the object of this property is an inline ems:WorkBreakdownStructure resource.

Examples

• EMS 1.0 Primer, Listing of ASAP Scenario
• EMS 1.0 Primer, Listing of Scenario 5721
• EMS 1.0 Primer, Listing of Scenario with Triangular Distribution

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