Like any other database-based application, information in ServiceNow instances is stored in structured and related tables, which consist of columns and rows of records. Tables can be related to each other in the following ways:

• Extensions: A table in ServiceNow may extend an existing table (parent class), thereby ensuring that all of the fields of the parent class are included as part of the child table. For example, the Incident table extends the Task table, and thus the Incident table has all of the fields that are available in the Task table.
• One to many: A table can consist of a field that refers to a record on another table. For example, the assigned to (assigned_to) field in the Incident record might contain a reference to a record in the users (sys_users) table. The Reference, Glide List, and Document ID field types can be added to create a one-to-many...