The Tool Desk
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What distinguishes the three data models?
| Model | Question it answers | Typical contents | Use it when |
|---|---|---|---|
| Conceptual | What information matters in this business domain? | Principal concepts or entities and their relationships, with minimal implementation detail. | Stakeholders need to agree on scope, vocabulary, and business relationships. |
| Logical | How should the domain’s information be organized? | Entities, attributes, identifiers, relationships, and business rules, independent of a particular physical database. | Analysts and designers need to validate data structure before deciding implementation details. |
| Physical | How will the chosen database store and enforce the design? | DBMS-specific tables and columns, data types, keys, constraints, naming, and relevant indexes or storage choices. | Database designers and developers are preparing implementation, deployment, or tuning. |
Conceptual: agree on meaning and scope
A conceptual model describes the important things in a domain and how they relate. For example, a team might identify customers, orders, and products, then agree on the business relationships among them. It is deliberately abstract: the purpose is to settle what the organization means, not how a database will store it. SAP’s Conceptual and Logical Data Model Quick Reference, version 16.7 SP3 describes conceptual modeling as identifying principal entities, attributes, and relationships at a more abstract level than logical or physical models. Visual Paradigm similarly frames it around business requirements.
Logical: define the information structure
A logical model adds the structure needed to describe the domain: attributes, identifiers, relationships, and applicable business rules. It remains independent of a specific physical database implementation. This makes it useful for reviewing whether the design represents the business correctly before database-specific decisions constrain it. SAP describes the logical model as analyzing system structure independently of a particular physical database implementation; ER/Studio likewise recommends addressing business and functional requirements in logical design before physical design.
Physical: make the design implementable
A physical model translates the logical design into choices for a target DBMS. It specifies concrete tables and columns, data types, keys, constraints, names, and relevant indexes or storage settings. Those choices must fit the selected system’s conventions and restrictions. Visual Paradigm’s Database Designer’s Guide calls the physical ERD “the actual design blueprint of a relational database”; that description applies to the implementation-level diagram, not to every kind of data model.
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How to choose the right level
- Start conceptual when discussion is still about what the business means by a customer, order, product, event, or other domain concept. Use it to align stakeholders on scope and relationships.
- Move to logical when the team must settle how concepts relate, which attributes identify or describe them, and what business rules apply. Keep the design independent of a specific database while validating its structure.
- Use physical after selecting a database technology and when the team needs a buildable schema. Make DBMS-specific choices explicit so the design can be implemented and reviewed.
- Clarify the request if someone asks for “the data model.” Ask who needs it and what decision they are making; the phrase can mean any of these levels.
A project can use only the level needed for its decision, or move through all three as its needs become more concrete. Treating them as a progression is useful, but producing three separate formal deliverables is not a requirement.
How to compare two modeling approaches
When deciding between levels—or between designs—compare the abstraction, intended audience, decision at hand, and dependence on a particular technology. Also consider how much detail is useful now, whether a DBMS has been selected, and whether reviewers need to trace implementation structures back to business requirements.
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If more than one database platform is still under consideration, keep the logical design independent enough to compare possible implementations. Where practical, defer platform-specific decisions to physical design. That follows from the distinction between implementation-independent logical structure and DBMS-specific physical choices; it is a workflow recommendation, not a guarantee that every logical design will transfer unchanged between systems.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How to keep models connected
Use links or mappings between levels when teams need to explain how the implementation corresponds to business requirements. Do not assume every logical entity becomes exactly one physical object: DoDAF’s DIV-3 physical data model guidance notes that mappings can be one-to-many or many-to-many. Transformations and synchronization features in modeling software can help track changes across models, but they do not replace review of the transformed design. The appropriate mapping depends on the design and target system.
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