This is an article which is useful for people studying the Customization and configuration exam but relationships are good to know if you using CRM.
Relationships and mappings are 20 percent of the Customization and configuration certification so it’s vital you know the different types and how they work.
This article explains the various relationship types you have in CRM 4
The relationship type defines the cascading rules for a relationship. The following table describes the possible relationship types.
|System||A parental relationship type automatically defined by Microsoft Dynamics CRM for system entity relationships. You cannot modify this kind of relationship.|
|Parental||All operations on the parent entity instance are propagated to the child entity instances (cascade all):
|Referential||Operations are not cascaded between entities (cascade none):
|Referential, Restricted||The entity instance can only be deleted if it has no related entity instances. Otherwise, this relationship type is the same as referential.|
|Configurable Cascading||Cascading rules can be configured for most actions. For system relationships, you can select the cascading rules for all actions except merge or delete. For custom relationships, cascading rules can be selected for all actions except merge. Cascading on merge is dependent on the referenced entity. If the referenced entity is an account, contact, or lead, the action cascades. Otherwise, it does not.|
This article also gives a good overview of the relationships in CRM
Finally here are a couple of well written articles with videos links
Many to Many
Self- Referential Relationships