The lower part of the service value system contains continual improvement. If you'll look at the ITIL 4 diagrams here, you'll notice that it is called out in the purple block. While continual improvement is one of the 34 distinct ITIL practices, it is also called out in the service value chain, too. So why is continual improvement pulled out in addition to the fact that it's also a practice? Well, it's because continual improvement is that important. In everything you do in your organization, you should always be trying to improve. And when you look at this from the ITIL 4 exam perspective, continual improvement comes up twice.
First, you have to be able to recall the purpose of the continual improvement practice - and notice the keyword there is recall. That means you have to be able to know it word for word and be able to identify that definition on the exam. Second, you also need to be able to explain or discuss how continual improvement and the continual improvement model fits within the service value chain and the service value system. So you're going to spend a lot of time in the articles here at itil.diontraning.com and the online course talking specifically about continual improvement.
Now as already mentioned, you have to be able to recall the definition. And here is the definition: the purpose of the continual improvement practice is to align the organization's practices and services with changing business needs through the ongoing identification and improvement of services, service components, practices, or elements that are involved in the efficient and effective management of products and services. And yes, it is a very long definition. But you need to be able to know it because if the exam gives you something where there's a fill-in-the-blanks question, you have to be able to pull in the right word. Also, if they give you this definition, you need to be able to identify that it is the continual improvement practice. That's the level of knowledge you need for the recall part of the exam.