# Data model design: objects, junctions and Schema Builder

*Platform App Builder Study Guide · Data Modeling and Management · Last updated October 25, 2026 · https://www.certifyforce.com/study-guide/platform-app-builder/data-modeling-and-management/data-model-design-objects-junctions-and-schema-builder*

How to turn a requirement into objects, fields, record types and relationships: when a related custom object beats more fields, how to build a junction object, which structures force a lookup instead of master-detail, what Schema Builder can and can't do, and how to read Salesforce Architects data model diagrams.

- Certification: Salesforce Platform App Builder
- Exam section: Data Modeling and Management
- Study guide: https://www.certifyforce.com/study-guide/platform-app-builder

**Official exam objective:**

> Given a scenario, determine the appropriate data model.

## What the exam expects

- Decide whether a requirement needs a field, a record type, a related custom object or a junction object.
- Build a junction object the recommended way.
- Recognise structures that must be a lookup instead of master-detail.
- Know what Schema Builder can add and its considerations.
- Read a Salesforce Architects entity relationship diagram (ERD).

Key terms:
- **Data model:** the objects and fields in an app; objects are tables, fields columns, records rows.
- **Junction object:** a custom object with two master-detail relationships linking two objects many-to-many.
- **Self-relationship:** a relationship from an object to itself; always a lookup.
- **Hierarchical relationship:** a special lookup available only on the User object.
- **Record type:** a variant of one object with its own business process, picklist values and page layout.

## Key facts

| Fact | Detail | Source |
|---|---|---|
| Junction object | A custom object with two master-detail relationships | [Many-to-Many Relationship](https://help.salesforce.com/s/articleView?id=platform.relationships_manytomany.htm&type=5) |
| Self-relationships | Must be a lookup; a record can't link to itself | [Relationship Considerations](https://help.salesforce.com/s/articleView?id=platform.relationships_considerations.htm&type=5) |
| Many-to-many self-relationship | Not supported: a junction's two masters can't be the same object | [Relationship Considerations](https://help.salesforce.com/s/articleView?id=platform.relationships_considerations.htm&type=5) |
| Detail levels | Up to 3 custom detail levels | [Relationship Considerations](https://help.salesforce.com/s/articleView?id=platform.relationships_considerations.htm&type=5) |
| Standard objects in master-detail | Can be the master; can't be the detail of a custom object | [Relationships Overview](https://help.salesforce.com/s/articleView?id=platform.overview_of_custom_object_relationships.htm&type=5), [Relationship Considerations](https://help.salesforce.com/s/articleView?id=platform.relationships_considerations.htm&type=5) |
| Relationship limits | Up to two master-detail and 40 total relationships per custom object | [Relationships Overview](https://help.salesforce.com/s/articleView?id=platform.overview_of_custom_object_relationships.htm&type=5) |
| Schema Builder adds | Custom objects, lookups, master-detail, all custom fields except Geolocation | [Schema Builder](https://help.salesforce.com/s/articleView?id=platform.schema_builder.htm&type=5) |
| Schema Builder field access | New custom fields visible and editable for internal profiles by default | [Schema Builder Considerations](https://help.salesforce.com/s/articleView?id=platform.schema_builder_considerations.htm&type=5) |
| Schema Builder limits | No schema export; Auto-Layout can't be undone; zoom not saved | [Schema Builder Considerations](https://help.salesforce.com/s/articleView?id=platform.schema_builder_considerations.htm&type=5) |

## Check yourself

- Why can't a junction object's two master-detail fields both point to the same object?
- When should a requirement become a record type instead of a new custom object?
- Why does a new field built in Schema Builder need a field-level security review?
- Which custom field type can't be added in Schema Builder?

## Sources

- [Considerations for Object Relationships](https://help.salesforce.com/s/articleView?id=platform.relationships_considerations.htm&type=5)
- [Object Relationships Overview](https://help.salesforce.com/s/articleView?id=platform.overview_of_custom_object_relationships.htm&type=5)
- [Create a Many-to-Many Object Relationship](https://help.salesforce.com/s/articleView?id=platform.relationships_manytomany.htm&type=5)
- [Design Your Own Data Model With Schema Builder](https://help.salesforce.com/s/articleView?id=platform.schema_builder.htm&type=5)
- [Schema Builder Considerations](https://help.salesforce.com/s/articleView?id=platform.schema_builder_considerations.htm&type=5)
- [Salesforce Data Model Diagrams](https://architect.salesforce.com/docs/architect/reference-diagrams/guide/data-model-notation)
- [Optimize Customer Data with Standard and Custom Objects](https://trailhead.salesforce.com/content/learn/modules/data_modeling/objects_intro)
- [Create Object Relationships](https://trailhead.salesforce.com/content/learn/modules/data_modeling/object_relationships)
- [Tailor Business Processes to Different Record Types Users](https://help.salesforce.com/s/articleView?id=platform.customize_recordtype.htm&type=5)

## About the full unit

The "Core concepts", "Exam traps" and "Worked scenario" sections of this unit, its 14 linked practice questions, and unlimited timed mock exams are included with the Platform App Builder pack (USD $19): https://www.certifyforce.com/practice-exams