In the early 80's and 90's many different methodologies and models were being used for designing software programs, business systems, and database development. A standard was necessary. Booch, Rumbaugh, and Jacobson championed the cause of creating a standardized method for software modeling. In 1997, Booch, Rumbaugh, and Jacobson's Unified Modeling Language was accepted as the defacto standard. Industry leaders like Microsoft, Oracle, IBM, and HP accepted UML as the standard (OMG.org)
UML is defined by its founders; Booch, Rumbaugh, Jacobson (1998), as a standard "modeling language for writing software blueprints." Modeling is important whether you are building a house, designing a software program, defining an enterprise infrastructure or designing a database. The development process of any project must be followed to ensure the scope of a project is laid out, the needs of the users and reason for the project are documented and understood, programmer's or developers need to be clear about their tasks, the end product needs documentation, testing and an implementation plan.
I am describing the System Life Cycle Development Model. UML is a graphical based tool that allows for deliverables in all stages of the model. A model allows all the stakeholders involved to Visualize, Specify, Construct, and Document the project all from one set of plans or blueprints.
Models help all involved to visualize a system as it is or as we want it to be. This can be used by all stakeholders from users on the project team working on usability, screen shots and placement, to analysts and programmers.
Systems analysis is the part of the systems development life cycle in which you determine how the current information system functions and assess what users would like to have the new system work/perform or do. The Specify phase of UML is documenting the System Requirements...