root/gaphor/tags/gaphor-0.12.1/doc/model.txt

UML Model
~~~~~~~~~

The UML model that should hold all information. It would be nice if the model
looks like the UML MetaModel. In order to keep the model consistent a lot of
bi-directional relations have to be made. Those relations have a multiplicity
of '0..1', '1', '1..*' or '*'. For simplicity we reduce this to '1' and '*'.

For the objects that have a multiplicity of 1 we can simply assign a
value to the attribute. If a new value is assigned to the value we can simply
replace it.

We also need some sort of Sequence object (a 'list-deluxe') that will allow us
to add and remove elements from the list. We can use the List object for that,
but we should check the object that is added to the list for its type. 


Signals
~~~~~~~
UML elements should emit signals if their state changes. This can be done
by means of the misc.signal.Signal class. All what's left is to define a
protocol (the arguments that the UML element supplies).

The following cases can occur:
1. Unidirectional relationships or attributes:
   a. Set data
   b. Set data and overwrite old data
   c. Remove the attribute
2. Bidirectional relationships
   a. multiplicity of '1'
   b. multiplicity of '*'

For non-sequence attributes we can do something like this

        def signal_handler(attribute_name, old_value, new_value, *custom_args):
            pass

where old_value and new_value is None (or the default value) in case no value
was set before.

For sequences we can only add and remove values. We can do this with the
same amount of attributes, only old_value will be one of 'add' or 'remove' and
new_value will contain the value that is added or removed.