Hi,
UML is really touted as a complete methodology that encompasses more than just design. It is a 'collection' of processess and artifacts.
In the space of 'data' - UML would use class diagrams. Class diagrams focus in on behaviour (functionality) and data together.
There are inherent problems using class diagrams to model data. Very oftern when you're finished you have to perform 'object to database mappings ' to have something of value.
One example is that class diagraming allows what is termed many to many associations between classes, whereas in logical data modeling this is considered bad practice.
The advantage to class diagrams is that you discover the functionality or behavior of classes. There are ways to do this with logical models, but they're not inherent to logical data modeling.
When or Why to use What - If you're development team is HONESTLY REALLY TRUTHFULLY using object oriented development. (Most places don't really do this) - UML and Class Diagrams work well with this
If you're using other methods of development (coding) or not true OO.... then you won't gain any advantage in UML.
Being a data modeler by nature..... I favor logical and physical data models.
Vmuisc