Fluent Validation is a popular .NET library that allows defining validation rules in a more fluent and flexible manner. It can be combined with Entity Framework to implement dynamic validation rules easily.

Data Annotations are attributes in .NET that can be applied to entity properties to enforce validation rules. They can be utilized in Entity Framework to ensure data integrity by defining constraints on entity properties.

In a multi-layered application, it's essential to enforce data consistency across layers. Implementing validation at the business logic layer ensures that all data manipulation goes through a central point where validation rules can be enforced uniformly. This approach also promotes code reuse and ensures that validation logic is not bypassed by direct access to the data access layer or presentation layer. Entity Framework's built-in validation attributes offer a convenient way to define validation rules directly within the data model, facilitating consistency and maintainability.

In a distributed system, data may originate from various sources, including external services. Handling validation in a separate service layer allows you to centralize validation logic, ensuring consistency regardless of the data source. By validating incoming data before passing it to Entity Framework, you can prevent invalid data from being persisted in the database, maintaining data integrity. Propagating validation errors to the calling layer is essential for providing meaningful feedback to the user or client application. This approach enables prompt error handling and validation feedback, enhancing the overall user experience.

Inheritance in a data model in Entity Framework primarily serves the purpose of code reuse. It allows for the creation of a hierarchy of classes where common properties and behaviors can be defined in a base class and inherited by derived classes, reducing redundancy and improving maintainability.

A common inheritance strategy used in Entity Framework is "Table per hierarchy," where all classes in the hierarchy are mapped to a single database table. This strategy utilizes a discriminator column to differentiate between different types within the hierarchy.

In the Table-Per-Type (TPT) inheritance strategy, Entity Framework creates a separate table for each concrete type in the inheritance hierarchy. This means that each subclass has its own table containing only its specific properties. This approach can lead to a normalized database schema but may result in more joins during querying.

Entity Framework treats owned entities as separate entities in the inheritance hierarchy. They are mapped to their own tables and do not participate in inheritance. However, complex types are not supported in inheritance hierarchies and cannot be used as base or derived types. They are treated as part of the containing entity and mapped to columns within the same table.

In Table-Per-Hierarchy (TPH), the discriminator column is used to determine the type of each row in the table. It stores a value indicating the type of the entity. It helps Entity Framework to map the data to the correct derived class.

When using Table-Per-Type (TPT), Entity Framework creates a separate table for each derived class in the inheritance hierarchy. Each table represents a concrete class, which includes the properties of both the base class and the derived class.