Direct and indirect Cost Estimation Methods (3)

Indirect Estimations by measuring the Functional Size

A different type of an indirect estimation is determining the functional size (instead of Story Points) and relating it to an empirical value describing which size can be implemented with specific personnel costs (often called productivity or efficiency). The basics for measuring the functional size are defined in the industry standard ISO/IEC 14143. They require the refinement of user stories to use cases.

Sample Use Case Diagram

A use case stands for a system behavior perceptible by an actor from outside of the system boundaries. Actors can be human system users as well as other systems or machines (hardware or software). An example is the use case diagram of a (highly simplified) Internet Booking Engine for flights shown in the accompanying picture. Within the system boundaries (shown as a rectangle with the label "Internet Booking Engine”) use cases are represented by ellipses. They are related to (used by) actors, which in the example below are a traveler and a Computer Reservation System (CRS). Their relation is indicated by lines.

Each use case stands for actions which can be described by base functional components (BFCs) respectively elementary processes. The use case “search flight” could, for example, consist of the following (simplified) elementary processes:

1. Traveler calls the dialog Flight Search.
2. Traveler enters the departure date.
3. Traveler enters the first letters of the destination (name or code).
4. System looks up for matching airports in the database and displays a list of found items showing names and codes.
5. Traveler selects a list entry and clicks on the button “Search”.
6. System sends a message of type “Flight Search Request” including the departure date and airport code to the CRS.
7. System receives a message of type “Flight Search Response” from the CRS and reads the fields departure time, arrival time, airline, flight number, class, price and currency of all flight records included.
8. System displays a table showing this information about all received flight records.

With the knowledge of these BFCs or elementary processes many measuring methods can be used to determine the functional size and, with the aid of an empirical value of the own productivity, the expected development costs.

Alternatives:

    Expert Estimations
    Indirect Estimations with Story Points

Book recommendation: "Cost Estimation in Agile Software Development"