The UML stands for Unified Modeling Language. It is christened a "language" since the representation involves predefined notations, semantics and rules - so all participants involved - stakeholders, analysts, developers, testers all interpret these diagrams the same way.
The UML is a representation method, providing for different views to detail the software system under design. Just like we have front elevation, floor plan, electrical plan, plumbing plan, in the construction industry, to document different aspects of the same building, UML offers a set of diagrams to represent varied views for a software system. Each of these diagrams have a specific perspective to deliver to the reader, and it makes sense to overlay multiple diagrams to get the complete picture. The UML was architected by the Object Management Group (OMG) and they continue to maintain the definition for the later releases. Visit OMG.org and UML.org for more information.
The UML is an analysis toolbox that allows authoring of specific details of the system, such as business processes, state changes of key objects in a system, etc.
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