UML is a modeling language that defines a standardized way to draw models of software systems. There are a number of different types of diagrams specified as part of the UML -
Component diagram and
Selecting the diagram is based on the purpose and the requirement. use case diagram used to say how the software can be implemented and it will not stress how it can be implemented. and also UML stress on Object oriented design principles ,where designing software on OOD will be helpful. The full specification for the UML is available from the <a href=”http://omg.org”>Object Management Group</a> who design/revise/manage the specification. It is a pretty detailed document though. There are a number of simpler overviews. Here’s <a href=”http://www.agilemodeling.com/style/useCaseDiagram.htm”>an example I found for use cases</a>.