[Zope-dev] Re: RFC: RelationAware class for relations betweenobjects

[Evan Simpson]

Shane Hathaway wrote:
> Well, Evan, I'm having a hard time interpreting the paper you referenced
> that way.  The paper seems to use "relation" and "relationship"  
> interchangeably.  What it describes are relationships and relationship
> sets.  A relationship set is a set of relationships of the same type.

Yup.  Since Relationship seems to be a natural class name for these 
thingies, I wanted to avoid calling individual things that they contain 
relationships.

> This one seems to use only the terms "relationship" and "relationship
> set".  In fact, the next chapter of the course introduces relations and
> the relational algebra, which are clearly distinct concepts from ERM.

Actually the next chapter starts off with "A row in a table represents a 
relationship among a set of values. Thus a table represents a collection 
of relationships." :-)  Of course, this is consistent with what you 
state above.  I'm happy to call them whatever, I just wanted to try to 
avoid making up terminology when some exists.

> I'll ponder the rest of your email once we've agreed on common 
> definitions.

It basically boils down to defining a relationship by listing the roles 
of entities that it relates.  I also suggest declaring one-many type 
constraints among entitites in a relationship using a simple nested list 
notation.  No involvement of the entities' classes is required, and in 
fact the relationship definition can use strings for role names and 
avoid caring what class/type/kind of entity will fill that role 
altogether.  That might be problematic for APE, though, which I imagine 
would be happiest knowing exactly what class of object will fill each role.

Cheers,

Evan @ 4-am