Reference:
Entities are IT components that require management to deliver an IT service. Each entity has specific attributes and relationships to other IT processes that uniquely identify it. Entities contain alias fields and informational fields that ITSI associates with indexed events. Some statements that describe entities are:
B) An abstract (pseudo/logical) entity can be used to split by for a KPI, although no entity rules or filtering can be used to limit data to a specific service. An abstract entity is an entity that does not represent a physical host or device, but rather a logical grouping of data sources. For example, you can create an abstract entity for each business unit in your organization and use it to split by for a KPI that measures revenue or customer satisfaction. However, you cannot use entity rules or filtering to limit data to a specific service based on abstract entities, because they do not have alias fields that match indexed events.
D) To automatically restrict the KPI to only the entities in a particular service, select "Filter to Entities in Service". This option allows you to filter the data sources for a KPI by the entities that are assigned to the service. For example, if you have a service for web servers and you want to monitor the CPU load percent for each web server entity, you can select this option to ensure that only the events from those entities are used for the KPI calculation.