Subject entity \ feature has always been an integral part of Dynamics CRM at least since 3.0.
It gives a nice hierarchical way of organising and maintaining information.
To create or update Subject, navigate to Service Management area.
Similar to Subject entity, Category entity was introduced in CRM 2016 Update 1 (Service Pack 1 – On-Premise).
Navigate to Service Management area, to work with Category entity.
- Can we customize Subject or Category Entity?
We cannot customize Subject. It is available for Case, KB Articles, Product Catalog items and Sales Literature.
We can customize Category Entity.
We can create forms, add fields, views, business rules, dashboards etc.
Can create 1 – N relationship from Category to other entities.
We cannot create N- 1 or N-N relationship.
It has N-N relationship with Knowledge Article entity
- Is category User Owned or Organization Owned entity?
User Owned
- How are they rendered inside form?
Subject are rendered as tree structure
Category are rendered as lookup
We can also specify Auto-numbering for Categories
- What happens if a delete a Subject or category?
Deleting the subject will not delete its child record.
Deleting the category will delete its child record.
- Can we run advanced find on Subject and Categories?
We can do it on Categories, not on Subject.
- How does Subject render when used in advanced find filter condition? Tree view?
It renders like a lookup
Few considerations while migrating Subject records
Hope it helps..
Nishant Rana's Weblog 
We can create 1:N and N:1 relationship with Category. Only N:N is not possible
LikeLike