Source Relationship
Axiom SL supports 3 basic types of relationships between child and parent sources (nodes) that comprise data models. Technically there are more types of relationships. However, the resulting table configuration always comes down to the three variants that are listed below: 

One-to-one Many-to-one One or zero-to-one
One-to-many Many-to-one or zero Many or zero-to-one
One-to-one or zero One or zero-to-many
One-to-many or zero

 The selection of relationships depends on the original source data structure and on the scope of the expected results. 

Let us assume for example that we have a data model which consists of 2 sources (nodes) and the data model structure looks like:
With Join columns Deals.Customer Number = Customers.Customer Number.

Note: We always describe the relationship between nodes as a relationship between the parent node (Deals) and a child node (Customer).

1. Deals data table (parent)

Deal ID CustomerNumber
1 100
2 200

 Customer data table (child)

CustomerNumber CustomerName
100 Smith
200 Johns

 In this case, we would use ‘One-to-one’ relationship and the resulting data will look like:

Deal ID CustomerNumber CustomerName
1 100 Smith
2 200 Johns

 2. If the Deals table looks like:

Deal ID CustomerNumber
1 100
2 200
3 100
4 100

 With the same Customers table as in the previous example

CustomerNumber CustomerName
100 Smith
200 Johns

 The result of ‘One-to-one’ will look like:

Deal ID CustomerNumber CustomerName
1 100 Smith
2 200 Johns
3 100 Smith
4 100 Smith

 3. If the Deals table looks like:

Deal ID CustomerNumber
1 100
2 200

 And the Customer table looks like (notice that Customer Number 300 is absent from the Deals table):

CustomerNumber CustomerName
100 Smith
200 Johns
300 Edwards

 If we use One-to-one the result will be still identical to the first example:

Deal ID CustomerNumber CustomerName
1 100 Smith
2 200 Johns

 4. If the Deals table looks like:

Deal ID CustomerNumber
1 100
2 200
3 100
4 100

 And Customers table looks like (Customers table contains value ‘300’ missing in the deals table)

CustomerNumber CustomerName
100 Smith
200 Johns
300 Edwards

 The result of One-to-one, in this case, would be:

Deal ID CustomerNumber CustomerName
1 100 Smith
2 200 Johns
3 100 Smith
4 100 Smith

 5. If the Deals table looks like:

Deal ID CustomerNumber
1 100
2 200

And Customer table like:

CustomerNumber CustomerName
100 Smith
100 Simpson
200 Johns

If we use ‘Many-to-one’ relationship the result will look like:

Deal ID CustomerNumber CustomerName
1 100 Smith
1 100 Simpson
2 200 Johns

 6. If the Deals table looks like:

Deal ID CustomerNumber
1 100
2 200

 And Customer table like:

CustomerNumber CustomerName
100 Smith

 As you can see one of the deals does not have a corresponding record in the Customer table. If described by ‘One or zero-to-One’ the missing value will be replaced with ‘NULL’ value:

Deal ID CustomerNumber CustomerName
1 100 Smith
2 200 NULL

Please keep in mind that if we used ‘One-to-One’, the result would be:

Deal ID CustomerNumber CustomerName
1 100 Smith

7. If the Deals table looks like:

Deal ID CustomerNumber
1 100
2 200
3 300

 And Customer table like:

CustomerNumber CustomerName
100 Smith
100 Simpson
200 Johns

 And we would use ‘One or zero-to-one’ and result would be:

Deal ID CustomerNumber CustomerName
1 100 Smith
1 100 Simpson
2 200 Johns
3 300 NULL

Again, if we used ‘Many-to-One’ the result would be quite different:

Deal ID CustomerNumber CustomerName
1 100 Smith
1 100 Simpson
2 200 Johns

8. If the Deals table looks like:

Deal ID CustomerNumber
1 100
2 200
3 100
4 200

And Customer table like:

CustomerNumber CustomerName
100 Smith

And we use ‘One or zero-to-one’ we would get:

Deal ID CustomerNumber CustomerName
1 100 Smith
2 200 NULL
3 100 Smith
4 200 NULL

 9. If the Deals table looks like:

Deal ID CustomerNumber
1 100
2 200

 And Customer table like:

CustomerNumber CustomerName
100 Smith
100 Simpson
200 Johns
300 Edwards

In this case we would use ‘Many-to-one’ and the result would be;

Deal ID CustomerNumber CustomerName
1 100 Smith

 When you look at the data model using the Filter screen you may notice that in case of ‘One-to-one’, ‘One-to-many’, ‘One-to-one or zero’, ‘One-to-many or zero’, ‘One or zero-to-one’, ‘One or zero-to-many’ are shown as one record while ‘Many-to-one’, ‘Many or zero-to-one’ and ‘Many-to-one or zero’ are shown as 2 correlated tables.