Re: UML question

[Neil Zanella <nzanella cs mun ca>]

When you mention relationships what comes to mind is the conceptual schema
used to design a database. If this is what you are looking for then just
select ER-model from the drop down menu and choose the diamond to model
relationships. Entities are represented as rectangles which you can also
choose from the icons once you select ER-model from the drop down menu.
To model a many-to-many binary relationship you join the two entity sets
E1 and E2 to the relationship set R with line segments. If for each
participating entity in the entity set E1 the relationship associates
exactly one entity in the entity set E2 then the relationship R is
said to be many-to-one from E1 to E2. In this case you have two
choices for the notation, depending on your personal preference:

notation 1: an arrow points from entity set E1 to relationship set R
notation 2: an arrow points from relationship set R to entity set E2

For 1-1 relationships the same principle applies. You can either use:

notation 1: an arrow points from entity set E1 to relationship set R and
            another one from entity set E2 to relationship set R
notation 2: an arrow points from relationship set R to entity set E2 and
            another one from relationship set R to entity set E1

Also, to show that an entity fully participates in a relationship you
can make the corresponding line segment or arrow bold. Now dia makes
use of double lines to indicate total participation which is the
alternative notation to using bold lines. However dia does not
include a way of making double lines with arrows in the button
collection for the ER-diagram which is why I chose to adopt
the bold notation already in use elsewhere. Also dia's ER-model
doublelines are not straight lines which is the convention I have
always seen for ER-diagrams. But you can choose regular lines from
the menu above.

Now if you are working with object oriented rather than relational
databases then you may be looking for something different than what
I describe. UML is different from the ER-modelling language I describe.

Does this help?

Bye,

Neil

On Sat, 24 Nov 2001 atrauba workingmachines com wrote:

> Hi. A quick question.
>
> How do I represent an association between classes? For example, a
> many-one relationship. This is real basic, and I see an example in the
> UML tutorial, but I still can't figure out how to actually do it. By the
> way, I'm running version  0.88.1
>
> Thanks
>
> Andrew Trauba
> Working Machines Corp.
>
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