Final answer:
UML diagrams are essential throughout the software development life cycle phases, providing visual documentation and aiding communication for complex processes in software development.
Step-by-step explanation:
In the context of the software development life cycles (SDLC), the diagrams that serve as key documents in each phase of SDLC are represented by UML (Unified Modeling Language). UML diagrams are versatile and can be used during various stages of software development, from requirement gathering to design and documentation. They help illustrate, specify, and document the artifacts of software systems.During the requirements gathering phase, a UML use case diagram is used to define the system's functionalities. In the design phase, UML class diagrams and sequence diagrams are commonly used to model the system's structure and behavior. In the implementation phase, UML component and deployment diagrams help in visualizing the physical architecture of the software.
Examples of UML diagrams include use case diagrams for requirements, class diagrams for design, sequence diagrams for dynamic behavior, and activity diagrams for workflows. Each of these UML diagrams aids in the clear communication of complex software structures and processes among the development team and stakeholders, thus ensuring that the software is developed according to specifications.