Tool for UML Use Case Diagrams (TUCD).
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This tool is intended for use case diagrams (UCDs) that
are used in UML.

More about the drawing of UCDs can be found in chapter 6 of the
user's guide and more about the use of this notation technique can be 
found in appendix A of the user's guide.

Diagram editing in general.
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Diagrams that are made by a diagram editor are a special
kind of graph consisting of nodes and edges and with a certain 
representation. In the representation of a graph, nodes and edges are 
shown as shapes (boxes, lines, diamonds etc.).

Documents should satisfy certain constraints. Most constraints 
are specific for the particular diagram technique supported by the 
editor. In the editors there are three kinds of constraints:
 
1. Built-in constraints which are constraints which can never be 
violated because there is no command in the user interface to achieve 
that.
 
2. Immediately enforced constraints: when you perform a command that 
would violate a constraint that is immediately enforced, this command 
is rejected immediately by the editor and a pop-up window with an error 
message is displayed.
 
3. Soft constraints which are constraints that can be violated.
Soft constraints are checked by the editor when the Check Document 
from the Document menu is issued by you. Check Document displays a list 
of error messages in a pop-up window. As opposed to the previous two 
classes of constraints, you are responsible for correcting the diagram.


