lørdag den 27. september 2008

The V-model

The EN50126 process is based on a general lifecycle view; the lifecycle starts when the product (e.g. an interlocking system, a train, an LED-lamp etc.) is in a concept phase. Then the product is developed, approved and put into operation and finally it is disposed. This lifecycle is expressed in the V-model, see Figure 10 from EN 50126 below.


Please note the V-model can be viewed as a time-line, which is bended down to form a "V". The product moves sequentially from phase 1, "Concept", to phase 2, "System definition and application conditions", etc.

The V-model is created (by the working group) in order to handle all Railway systems - simple as well as complex.

In the daily life, the fourteen phases of the V-model can be compiled and simplified into a model that smoothly fits into the product in question.
However, the main idea of viewing a product as going through life-cycle phases, on a V-shaped time-line, should be intact.

Example 1:

We would like to install entertainment video screens in a train fleet. For this product, it should be sufficient with three phases: "Design", "Installation" and "Operation". The V-model can then be compiled and simplified into the Figure below:

Example 2:

A more complex system, like e.g. a new supervisory system in a major city, controlling many sub stations, is planned to be set into service in steps: Mission 1 includes the first 10 sub station on a single line, Mission 2 includes all stations on the line etc.; until the Final mission, where all sub stations in the city are supervised.
For such a system, the V-model can be viewed as a life-cycle line, where you step back to a former appropriate phase each time a mission has reached phase "Operation" and the preparation for the next mission starts. For example, the project might step back to phase "Design and Implementation of mission 2" once the phase "Operation of mission 1" has been reached, See the Figure below:

Next chapter >> 2.3 Verification, Validation and Assessment

Focus on the Source (EN50126:1999)

The life-cycle concept is explained already in the scope of EN 50126, chapter 1.1:

"This European Standard: - defines a process, based on the system lifecycle and tasks within it, for managing RAMS;"

In chapter 5 is Figure 10 (from above) explained:

This standard represents the system lifecycle sequentially. This representation shows individual phases and the links between phases. Other lifecycle representations are widespread within industry and include the ”V” model.

A ”V” representation of the lifecycle contained within this standard is shown in figure 10. The top-down branch (left side) is generally called development and is a refining process ending with the manufacturing of system components. The bottom-up branch (right side) is related to the assembly, the installation, the receipt and then the operation of the whole system.

And finally is chapter 6, describing each phase in the V-model.

Ingen kommentarer: