 now discuss is the so-called V model. The V model is an adaptation of the waterfall process which is still reasonably popular especially if you go into systems engineering so parts where you develop software together with other components like hardware electronics and what you have is you have the so-called or you have the left side of the V which is pretty much like the waterfall so you have specification activities you have design activities and you have implementation activities and they are sequential they are thought to be sequential so you finish the specification you finish the design you finish the implementation but then you have corresponding things on the right side of the V model and that's why it's called the V model because the shape if you draw it properly resembles the letter V. So what happens here is we implement small units at a time so we test them here and that is unit testing then we have the design and that has to do with breaking down the system into smaller components so what we do here is we integrate so we do integration testing so instead of having just a small part of the system and we test we put several components together and we test them together and at the end we have the entire system and we do system testing what is often also included here I'll just write it over is acceptance testing more on that will come in the testing lectures but essentially this test the entire system acceptance testing is testing that is done with or by the customer so it has much more to do with is this acceptable whereas the system is much closer to the requirement statements that we have and there is one thing in the V here that is special in terms of the timing it looks like we start specification then we do design then we do implementation then we do this and so on but what happens is as soon as the specification is done we have this corresponding step on the testing side so what happens then is actually that the planning of the system testing is starting already when this is done so the design is not there the implementation is not there but you can already plan and maybe already implement some kind of tests very often we do manual testing here for example you develop a car you drive the car around and test it according to a plan so you can start doing this plan here and the same goes for the other steps and well as soon as you have done the implementation you can directly start testing so this arrow here is still in place but essentially these testing activities are often very very time intensive so it's good that as soon as the specification is done you can already start setting this up planning this essentially so this is a model that is very much still used in practice there are of course sometimes adaptations because of the same issues we had before so maybe sometimes you want to go back here but you should be aware that if you go back this actually affects these arrows as well so if you decide to change a spec you also have to go back and change the testing plan so that's the V-Model