Software development is the major activity of Information Technology. We can engineer the software with the help of various process models. System Development Life Cycle (SDLC) is the base for all process models. All the other process models (for example RAD, Spiral model, Component based model, Increment model and even Agile model ) derived from SDLC. The Computer Aided software engineering (CASE) tools are software and we can use these tools to develop any application software. If we use these tools in the software development process we can reduce the manual work, efforts and save the time also. There are very low probability of failure the system. CASE tools are mostly associated with all phase of SDLC. Requirement engineering is the most important activity of software development life cycle. We have to assign more time on that phase because if we assign less priority and less time to that phase, we can't able to collect the proper requirement and this lead to unsatisfied deliverable. Unsatisfied and inefficient deliverables is not accepted by the client also. So there is a compulsory need to investigate some new CASE tools specially associated with Requirement Engineering which helps to optimize the software development process as well as increase the performance. As we know that Tool cannot work without providing knowledge. There are various ways to represent knowledge such as Inheritable knowledge, Relational Knowledge and Procedural Knowledge. This paper explores the CASE tool as well as various knowledge representation methods for Requirement engineering phase of Software Development Life Cycle and specially focused on requirement segregation.