Project Estimation using Scenarios

Defining estimation scenarios

The first stage in the steps to estimating a project was defined to be the definition of the scenarios to be supported in the solution.  The scenarios should be defined at as low a level of detail as possible, with the following diagram showing the example scenario definition.

Scenario definition

Scenario definition

Definition of the scenarios sizing

In the spreadsheet the light blue fields are those that you would normally fill in. The light purple fields are intended to fill in automatically based on the calibration parameters. If you prefer, however, it is suggested that you replace the calculated value with your own value where a better value is available. In this case I would suggest changing the colour of the cell so that you know this has been done later. I use bright highlighter yellow for this.The purple values are filled in from the “Calibration” sheet based on the complexity selected in the drop-down within those cells. The values represent typical operation counts for scenarios of the defined complexity.Scenario sizing calibrationThe scenario sizing information is drawn from the following part of the calibration sheet:Scenario calibration

As for all the calibration, the provided values are likely to be useful but the optimal values will depend on the business context of the estimator. It is suggested that the calibration should be adjusted from project to project until the most appropriate values are found. For a more rigorous approach a function-point counting style could be adopted on a specification of some suitable scenarios. The idea is to count the number of entities (c.f. database tables) that need to be managed by each scenario.

In the scenario definition sheet these filled in values are then summed at the bottom of the page, and each operation type is multiplied by a weighting factor to produce a total size. This can be seen at the bottom of the scenario definition sheet in the example:

Scenario sizing

Scenario sizing

The scenario sizing calculation

As can be seen, a standard “Operation Weight” is applied to each of the operation types within the columns of the estimation spreadsheet.  These are drawn from this section within the calibration sheet:

Scenario operation weight

Scenario operation weight

Operation weighting calibration

This process is similar in principle to function point analysis, but the constants have not been adjusted to provide a function point count. It would be possible to complete this and hence to provide an estimate very close to the true function point count of the solution. This, however, is left as an exercise for the reader since I don’t have access to a library of function point analysis data which would make it worthwhile.

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