Generation of unique IDs

[Daniel Salama]

I have a general question on the generation of unique IDs for things  
like customer number or invoice number, etc.

I'm using Seaside with Magma. I guess that I could design the app in  
Seaside so that there is a single user (e.g. seaside) logging into  
Magma for a particular application. I also assume that regardless of  
the number of users hitting the Seaside app, there is a single  
instance of the app managing multiple sessions. Is it safe to assume  
the following:

1) Communication between Seaside app and Magma is serialized in such  
a way that at any given moment, no two sessions will be performing  
the exact same operation? For example, if two users trying to delete  
the same object, will seaside serialize each request to Magma so that  
the second user will get a transaction commit error because the  
object is no longer there?
2) I maintain a dictionary of IDs in Magma so that when a new  
customer is created, the app looks up the next customer ID in the  
dictionary, and increments the count. I would assume that if I put  
this code along with the code to create the customer object in the  
same transaction, it should all happen atomically. My question is  
(and somehow related to the above question) if two users are creating  
different customers, what inherent fail safe mechanism exist so that  
the second transaction will get the updated next customer ID from the  
dictionary during its transaction process?
3) I believe the way squeak works with Dictionaries is that it tries  
to load it all in memory. Will it do the same with a Magma loaded  
Dictionary? The question is more geared to answer the following  
question: if I am in a transaction creating a new customer and I have  
the Dictionary element of customer IDs "locked", will the entire  
Dictionary be "locked"? If another transaction is occurring at the  
same moment where another user is creating a sales order and the app  
tries to get the next sales order number from the same dictionary,  
will it find a conflict?

Thanks for your input.

- Daniel