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This section covers allowable scenarios for extending existing core entities in the Ed-Fi data model.

2.1. Extend Domain Entity

An existing domain entity such as a Student can be extended to add new elements.*

• MAY MUST NOT contain any identity properties.
• MAY MUST NOT contain entity-level documentation.
• MUST contain at least one property.
• MAY MUST NOT contain properties included in the parent domain entity unless additional context is provided.
• MAY include any properties as optional single properties or optional collections.**
• MAY MUST NOT include required properties (as single properties or collections).

* There are some known exceptions for extending domain entities. See Unsupported Modifications for more details.

** An exception applies to collections of simple types. Only string and decimal simple types may be included as collections.

2.2. Extend Association Entity

An existing association entity such as the StudentParentAssociation entity can be extended to add new elements.***

• MAY MUST NOT contain any identity properties.
• MAY MUST NOT contain entity-level documentation.
• MUST contain at least one property.
• MAY MUST NOT contain properties included in the parent association unless additional context is provided.
• MAY include any properties as optional single properties or optional collections.****
• MAY MUST NOT include required properties (as single properties or collections).

*** There are some known exceptions for extending associations. See Unsupported Modifications for more details.

**** An exception applies to collections of simple types. Only string and decimal simple types may be included as collections.