Table, record and field
Table
Defines a collection and its structure. The Tables table sys_db_object has one record for each database table.
Record
One row representing an item such as an incident or user. Every record has a unique sys_id.
Field
One typed attribute or column, such as short description, opened date or caller reference.
CSA exam clue
A form displays one record; a list displays multiple records. Both are views of table data, not separate copies of it.
The System Dictionary describes the structure
Dictionary Entries sys_dictionary define every table and field. Administrators use dictionary entries to inspect or configure elements such as type, maximum length, default value, reference target, choices, attributes, dependencies and whether a field is mandatory or read-only.
incidentChange with care: changing a field type or length can affect existing data, integrations, scripts and child tables. Test schema changes outside production and verify dependent artifacts before promotion.
Reference fields connect records
- One-to-many: the many-side table stores a reference to the one-side record. Many incidents can reference one caller.
- Many-to-many: an intermediate junction table stores references to both sides. Users and roles use this pattern.
- Related list: a form can show matching records from another table based on a relationship.
- Display value: a reference usually shows a readable display field while storing the referenced record's identifier.
A reference is not plain display text. Filtering, permissions, reference qualifiers and the existence of the target record affect what users can choose or see.
Table extension reuses parent definitions
When a child table extends an extensible parent, it inherits the parent fields and can add its own. Incident, Problem and Change Request extend Task, so they share fields such as assignment and state while preserving class-specific behavior.
taskDefines shared fields and behaviorincidentInherits Task and adds incident-specific fieldssys_class_nameIdentifies the child class for extensible table recordsA parent-level change can affect every child. Before modifying a shared field, map the hierarchy with the Schema Map, Tables module or System Dictionary and test all impacted record types.
Dictionary overrides specialize inherited fields
A dictionary override changes selected behavior of an inherited field on a child table without changing the parent or sibling tables. Supported examples include a different default value, reference qualifier, attributes, calculation, dependency, display value, mandatory state or read-only state.
Example: specialize an inherited priority field
Suppose Task defines a default priority, but Incident needs a different default. An override on the Incident child table can change that inherited default while leaving Task, Problem and Change Request unchanged.
Overrides themselves can flow farther down the hierarchy. If another table extends the child, confirm whether it should inherit the child override or needs an additional override of its own.
Troubleshoot an unexpected field or value
- Confirm the table and class: check the record's actual table and
sys_class_name. - Open the dictionary entry: verify type, reference, default, attributes and scope.
- Trace inheritance: determine whether the field is defined on the current table or a parent.
- Review overrides: inspect overrides at every relevant parent/child level.
- Check configuration layers: UI Policies, Data Policies, ACLs, Business Rules and Client Scripts can alter behavior without changing the dictionary definition.
- Inspect reference configuration: target table, qualifier, display field and user access.
- Test all channels: form, list, import and API behavior may expose different controls.
- Retest child tables: a parent dictionary change can have wider impact than the original request suggests.
ServiceNow CSA practice checks
Which table defines every table and field in the instance?
Best answer: Dictionary Entries sys_dictionary, also called the System Dictionary.
Incident inherits assignment fields from which concept?
Best answer: table extension. Incident is a child of Task and inherits its parent fields.
Incident needs an inherited field to be mandatory without changing Problem. What fits?
Best answer: a dictionary override for the inherited field on the Incident table, subject to scope and platform support.
Frequently asked questions
What is the difference between a ServiceNow table, record and field?
A table defines a structured collection of data, a record is one row in that table, and a field is one typed value or column on each record. Forms show one record while lists show multiple records.
What does the ServiceNow System Dictionary contain?
The Dictionary Entries table defines tables and fields, including data type, maximum length, default value, reference configuration and other attributes. A collection-type entry represents a table.
What happens when one ServiceNow table extends another?
The child table inherits the parent table's fields and functionality and can add fields of its own. Incident, Problem and Change Request are examples of child tables extending Task.
What is a dictionary override?
A dictionary override changes selected behavior of an inherited parent field for a child table without changing that field for the parent or sibling tables.
Official ServiceNow references
Use the current ServiceNow documentation for tables and data models, table extension and classes, the Dictionary Entry form, dictionary overrides and global default fields. Capabilities vary by release, scope and entitlement.