Development cycle

There exist various types of development cycles entering the realization of a Logiciel. These cycles will take into account all the stages of the design of a software.

Big families

This cycle is inherited the building. This model rests on the following assumptions;

one cannot build the roof before the foundations;
the consequences of a modification upstream of the cycle have an major impact on the costs downstream (one can imagine the manufacture of a mould in the industry of the plastic).

The traditional phases of development are simply carried out the ones after the others, with a return on the preceding ones, even with the whole beginning of the cycle. The development process using a cycle in cascade carries out phases which have as characteristics:

to produce the deliverable as a preliminary definite ones;
to finish with an exact date;
to finish only when the deliverable ones are considered to be satisfactory at the time of a stage of validation-checking.

Cycle out of V

The model of the cycle out of V was imagined to mitigate the problem of reactivity of the model in cascade. This model is an improvement of the model in cascade which allows in the event of anomaly, to limit a return at the preceding stages. The phases of the rising part, must return information on the phases in opposite when defects are detected in order to improve the logiciel.
Moreover the cycle out of V the need highlights for anticipating and for preparing in the downward stages the " waited " future rising stages: thus waited tests of validation definite at the time of the specifications, are awaited unit tests are defined at the time of the design, etc

The cycle out of V became a standard of the industry of the Développement of software and Project management since the Années 1980.

The development takes again the various stages of the cycle out of V. By the implementation of successive versions, the cycle starts again by offering an increasingly complete and hard product.

One separates the activities from the Artéfacts, an artefact being the product resulting from an activity. Thus, one applies a cycle of the type Roue of Deming to the production of a documentation, a code, a test, etc

Paid to an activity of the project management type, the first phase will be that of

feasibility: the acceptance of a new need
development: it is imagined how one will carry it out
manufacture: construction
the transition: all is implemented to deliver to the customer

The iterative cycle is not a Bijection with the cycle out of V of the type

feasibility = Spécification S
development = Architecture
prototype manufacture = Développement
transition = tests

Knowing that each iteration never exceeds eight weeks, this tactic is thus impossible. In fact, the idea is to deliver as soon as possible something which can be tested by the customer. One can indeed carry out several iterations on a documentation such as architecture. Same manner, if a document is only one artefact among others, should not be obtained a complete document. One will prefer to use the law of Pareto: not to pass 80% of the effort out of the 20% remainder.

The difference between a PDCA and an iteration is the duration: it must be short and regular whereas a Roue of Deming applied to an organization of 300 people takes several months, even several years.

Comparison of the approaches Cascades, V and Iterative

The cycle out of V originates in Heavy industry. The characteristic of this medium is that the phase which follows requires much more resources than the preceding one.
For example, to manufacture an object in Plastic,

a Research department will design the product,
then prints of moulds will be machined and placed in carcasses to receive plastic by injection
and once the prototype is correct, one passes to a phase of production.

It should be known that for a simple object such as a plastic cup, the design is a business of a handle of weeks (either a few thousands of Euro S) whereas a mould (impressed + carcass) requires several months of manufacture and several hundreds of thousands of euros.

Consequently, in such a context, for good to manage its project, it is important not to neglect the validation of each stage under penalty of seeing it skidding.

This phenomenon even intervenes on software building sites joining together of tens of the hundreds of people. The decisions of the leadership team or architect of project impact so much engineers for such durations that it is to better make sure of the validity of each stage.

In addition, to limit the Entropy system consisted the team-project, it is necessary to formalize by documents (even tools)

the process
the Besoin S
the software specifications
the software Architecture
the tests

In the case of a software project implying a dozen people during one to two years, the configuration is not any more the same one; indeed, with such project one lays out:

of a greater reactivity due to

a geographical proximity
a facility (relative) of communication

of a factor of cost limited between each stage

Also, it is possible to direct towards methods of development known as nimble by decreasing the formalism and by multiplying the number of cycles (iterative operation).

Some methodologies

See too

nimble Method
: Category: Method of software development
Quality of the computing systems

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