In Domain-Driven Design (DDD), the choice between modeling something as an Entity or a Value Object hinges on whether it has an intrinsic identity that persists over time (Entity) or if it's purely defined by its attributes and can be treated as immutable and replaceable (Value Object). You're right that Entities have continuity through an ID (e.g., even if attributes change, it's the "same" thing), while Value Objects are equal if their values match, and they're often immutable.For your case—storing an employee's past salaries in an employeeSalaries table and displaying them as a list—let's break it down step by step to help you decide. I'll focus on practical implications, including domain modeling, persistence, and usage.

Step 1: Analyze the Domain Semantics

• What does a "salary" represent here? It's likely a historical record of an employee's compensation at a given time, e.g., attributes like amount, currency, startDate, endDate, reasonForChange (if any). These are descriptive and tied to the employee.

• Does it have independent identity? Ask: If two salary records have identical attributes (e.g., same amount, dates), are they interchangeable? Probably yes—they describe the same "fact" about the employee's history. You wouldn't care about distinguishing them beyond their values.

• Lifecycle and mutability: Past salaries are historical facts; they shouldn't change once recorded (immutable). If a salary needs "updating," you'd likely add a new record rather than modify an old one (e.g., for corrections or adjustments). This leans toward Value Object.

• Relationships: Salaries belong to an Employee (an Entity). They're not standalone; they're part of the Employee's aggregate. In a list display, you're just showing a chronology of values.

If the answer to "Does this thing need to be tracked uniquely over time, even if its attributes change?" is no, it's probably a Value Object.

Step 2: Practical Considerations for Your Scenario

• Display as a list: This sounds like a read-only view of historical data. Value Objects work well here because you can treat the list as a collection of immutable structs. Equality checks (e.g., for duplicates) would be based on values, not IDs.

• Database storage (employeeSalaries table):

  • Even if you use a separate table, that doesn't force it to be an Entity—that's an implementation detail. Value Objects can be persisted in normalized tables (e.g., with a foreign key to the Employee ID) for efficiency, especially for large histories.

  • If it's a Value Object, you might not need a surrogate ID (auto-increment) per row unless required for ORM tooling or querying. Instead, a composite key (e.g., EmployeeID + StartDate) could ensure uniqueness.

  • If you foresee needing to reference a specific salary record elsewhere (e.g., linking to audit logs, bonuses tied to a exact salary period, or updating metadata like "approval date"), an ID might be useful—pushing toward Entity.

• Common pitfalls in practice:

  • Over-entity-izing: Many devs default to Entities for everything with a table row because ORMs (like Hibernate or Entity Framework) make it easy with IDs. But this can lead to anemic models where everything has an ID but no real identity matters.

  • Immutability enforcement: Value Objects encourage better design by making things immutable, reducing bugs from accidental mutations.

  • Performance/Queries: For lists, Value Objects simplify queries (no need for extra joins if embedded, but since you're using a separate table, it's fine either way).

Step 3: Pros and ConsHere's a comparison to help weigh it:

AspectValue Object ApproachEntity ApproachIdentityNo ID needed; equality by attributes (e.g., amount + dates).Requires an ID (e.g., UUID or auto-increment); equality by ID.MutabilityImmutable by design—create new ones for changes.Can be mutable, but you'd still version history.Domain FitGreat for descriptive, historical data like salaries.Better if salaries have their own lifecycle (e.g., approvals, revisions).Code Exampleclass Salary { BigDecimal amount; LocalDate start; ... } (in Employee's collection).class SalaryEntity { UUID id; BigDecimal amount; ... } (repository for CRUD).PersistenceStore in table with FK to Employee; optional composite key.Store with PK ID + FK; easier for relations if needed.ProsSimpler model; encourages immutability; easier equality/comparison; less boilerplate.Easier to reference/update individually; fits if auditing or linking required.ConsHarder to reference a specific instance if needs arise later; might need to refactor if domain evolves.Adds unnecessary identity if not needed; can bloat model with IDs everywhere.When to ChooseIf salaries are just "values over time" for display/history.If you need to track changes to the salary record itself (e.g., "this salary was adjusted due to error").

RecommendationBased on what you've described (historical list for display, no mention of complex operations like individual updates or references), model employeeSalaries as Value Objects. Embed them as a collection within the Employee aggregate. This keeps your domain model clean and focused on the business meaning—salaries are attributes of the employee's history, not independent "things" with lifecycles.

• Implementation Tip: In code (assuming something like Java/C#), make Salary a record/class with equals/hashCode based on all fields. In the database, use a separate table for scalability, but treat it as serializing the Value Object collection.

• If things change: If you later need to add features like attaching documents to a specific salary or auditing changes to the record (not the salary value), you can evolve it to an Entity. Start simple.

If this doesn't match your domain (e.g., if salaries involve more behavior or relationships), provide more details like the full attributes or use cases, and I can refine this!