In this lesson, we are going to learn about V model. So if you have been in the software industry and you have been using the waterfall method, you must have seen when the time crunch is there in the end. We squeeze the testing phase and try to go through that testing phase as quickly as possible because the deadline is looming and we need to deploy the software. So this model was geared towards solving that problem, a little bit, in one sense. So if you look at the V-model, it looks very similar to the waterfall method, but it's just bent into a shape of a V. But if you look closely, the left side of the model is about project definition or the product definition, where it's getting finer and finer. So from the concept, you go to the requirement, and to the design, and to the implementation. And then the right side is showing all the validation steps that are corresponding to the steps on the left. All right, so for example, the verification and validation is corresponding to the requirements phase. So in the V-model, when you are doing your requirements, you start talking about your verification and validation. So you kind of talk about how are you going to do verification and validation when you are in the requirements phase. So what it basically means is that you're introducing the testing activities related to the testing phase earlier in the model. And then one more thing to talk about is you see that on the y-axis, it's increasing in the abstraction when you go from bottom to the top. And then if you go from the left to right, it kind of shows the project completion. So as we talked about, the basic idea behind V-model is that there is a lot of emphasis on the validation earlier in the process. If you look at it from the predictive and the adaptive scale, I would say that the V-model is very much a predictive model. Because it doesn't allow any kind of feedback or doesn't allow any kind of changes during the phases. It just allows you to introduce the verification earlier in the process. In terms of the benefits and the disadvantages of this model, in terms of advantages, it provides earlier detection of potential defects and the issues. Because if you're talking, in the requirement phase, how we're going to validate, sometimes you go, "these requirements are not correct, let's fix it." And so those are kind of the advantages of this model. And then in terms of the cons, it requires more upfront work because during the requirement phase, you are also going to talk about the validation of those requirements. So a little bit of extra work upfront. So when to use this model? Well, if there is ambiguity in the requirements, and then you want some kind of early validation, would help, then you can use V-model.