What is object relationship overview in salesforce?

Hi Laveena,

You can define different types of relationships by creating custom relationship fields on an object. Before you begin creating relationships, determine the type of relationship that suits your needs.Different types of relationships between objects in Salesforce determine how they handle data deletion, sharing, and required fields in page layouts. Let’s review the types of relationships.

Master-detail:Closely links objects together such that the master record controls certain behaviors of the detail and subdetail record. For example, you can define a two-object master-detail relationship, such as Account—Expense Report, that extends the relationship to subdetail records, such as Account—Expense Report—Expense Line Item. You can then perform operations across the master—detail—subdetail relationship.

Many-to-many: You can use master-detail relationships to model many-to-many relationships between any two objects. A many-to-many relationship allows each record of one object to be linked to multiple records from another object and vice versa.

For example, you create a custom object called “Bug” that relates to the standard case object such that a bug could be related to multiple cases and a case could also be related to multiple bugs.

Lookup: Links two objects together. Lookup relationships are similar to master-detail relationships, except they do not support sharing or roll-up summary fields. With a lookup relationship, you can:

• Link two different objects.
• Link an object with itself. For example, you might want to link a custom object called “Bug” with itself to show how two different bugs are related to the same problem.

External lookup: An external lookup relationship links a child standard, custom, or external object to a parent external object. When you create an external lookup relationship field, the standard External ID field on the parent external object is matched against the values of the child’s external lookup relationship field. External object field values come from an external data source.

Indirect lookup: An indirect lookup relationship links a child external object to a parent standard or custom object. When you create an indirect lookup relationship field on an external object, you specify the parent object field and the child object field to match and associate records in the relationship. Specifically, you select a custom unique, external ID field on the parent object to match against the child’s indirect lookup relationship field, whose values come from an external data source.

Hierarchical: A special lookup relationship available for only the user object. It lets users use a lookup field to associate one user with another that does not directly or indirectly refer to itself. For example, you can create a custom hierarchical relationship field to store each user's direct manager.