It is one of the crucial software engineer job interview questions. A System Context Diagram is a graphical representation of a system's interrelationships and dependencies, as well as its external environment. SCD can be created to help you understand the context of your system, which will help you better understand how to make decisions about it. SCDs are typically used in software development projects and can be either high-level or detailed. The diagram itself is made up of three basic parts: The main part of the diagram contains one or more systems, which are represented by boxes with labels for each element in the system. The elements are connected to each other by lines that represent how they interact with each other. This can include interactions between different elements within a single system (for example, two functions) or between different systems (for example, an API that connects to another API). The next part of SCD is the context section, which shows what elements outside of your system are relevant to it—for example, other systems that interact with yours through an API or customers who interact with your website through their web browsers. This section also includes information about any constraints on how these external elements interact with yours (such as regulations that govern how much data must be stored for legal reasons). Finally, there is the section on constraints, which lists any limitations or boundaries that limit what your system can do—for example, how much data it needs to store for legal reasons. The SCD is a very useful tool for understanding the scope of a project and making sure that you don't miss anything important along the way.