data-model-guide

name

data-model-guide

description

Use when designing a central in-memory data model / object database for a tool, editor, or engine: typed objects with properties, stable cross-references and sub-object ownership, change notification, undo/redo, and serialization. Triggers on prompts about a runtime object/property schema, referencing objects by stable id/GUID, observing/notifying changes, transactional edits and undo history, save/load with versioning/migration, or copy-on-write snapshots — even when the user doesn't name a specific model.

Data-Model Guidelines

Essentials

• One central model - Route tool/editor state through a single typed object store, not scattered structs, see references/object-model.md
• Stable ids, not pointers - Reference objects by id/GUID so storage can move, save, and reload, see references/references-and-ownership.md
• Make mutation observable - Edits go through the model so it can notify, undo, and persist, see references/change-notification.md

Object model

• Typed objects - Describe each type by a runtime schema, not a hand-written C struct, see references/object-model.md
• Property set per type - bool/int/float/string/reference/sub-object/buffer/array properties, see references/object-model.md
• Data-driven types - Add a type or property at runtime without recompiling, see references/object-model.md
• Separate metadata from instances - Type/schema lives once; instance data is just values, see references/object-model.md

References & ownership

• Strong = owning sub-object - A parent owns its sub-objects; deleting the parent deletes them, see references/references-and-ownership.md
• Weak = reference - A reference does not own; on delete it resolves to null, never dangles, see references/references-and-ownership.md
• Local vs global ids - Local ids inside a file, GUIDs for cross-file/cross-session links, see references/references-and-ownership.md
• Identity vs role - A GUID names a fixed identity; a name/path names a role that late-binds — default to GUIDs, see references/references-and-ownership.md

Prototypes & overrides

• Any object can be a prototype - Instances inherit all properties and store only overrides; resolve a property by walking the prototype chain, see references/prototypes.md
• Per-property override bitmask - One bit per property marks local-vs-inherited; sub-object sets track inherited / instantiated / removed children, see references/prototypes.md
• Serialize only deltas - Persist the prototype reference plus overrides; reconstruct inherited values on load, see references/prototypes.md

Mutation

• Change notification - Events, dirty flags, dependency recompute, batched per transaction, see references/change-notification.md
• Pull vs push - Poll a version number, or register callbacks; avoid notification storms, see references/change-notification.md
• Undo/redo - Record inverse ops or before/after snapshots into an undo journal, see references/undo-redo.md
• Transactions - Group many edits into one user-visible undo step, see references/undo-redo.md

Persistence

• Stable on-disk schema - Version the format; migrate old files into the new schema on load, see references/serialization.md
• References serialize by id - Persist ids/GUIDs, re-resolve on load, see references/serialization.md
• Deterministic output - Stable ordering for diff/version control; choose text vs binary, see references/serialization.md
• Save changes or re-spawn from assets - Persist member-level deltas for runtime state, asset references for content; POD serializes by default, see references/serialization.md
• ABI-stable struct evolution - Append fields at the end, add a leading size, never reorder/retype; semantic-version the API, see references/serialization.md
• Snapshots & threading - Publish immutable/copy-on-write versions for readers, see references/snapshots-and-threading.md

Gotchas

• A weak reference must resolve to null after its target is deleted; never leave it pointing at a recycled id.
• Reusing a freed object id lets a stale reference silently alias a different object — bump a generation or never reuse.
• Firing a notification synchronously inside a setter can re-enter the model mid-edit; queue and flush at transaction end.
• An undo entry that captured a pointer/index breaks once storage moves — capture ids and values, not addresses.
• External side effects (file writes, network) are not undoable; keep them out of the transactional journal.
• A loader that rejects unknown fields cannot open older OR newer files — migrate forward and ignore-or-preserve unknowns.
• Overriding a sub-object in an instance gives it a new id, so references to the prototype's original silently miss — resolve references through the override, don't store the new id everywhere.
• Allowing computed overrides (a property defined as an expression over the prototype's value) drags evaluation order and cycles into the data model — keep overrides concrete values.

Progressive Disclosure

• Read references/object-model.md - Load when defining typed objects, property kinds, or data-driven schemas
• Read references/references-and-ownership.md - Load when linking objects by id, modeling ownership, or handling deletes
• Read references/prototypes.md - Load when adding prefabs/templates/presets: prototype-instance inheritance, per-property overrides, override propagation
• Read references/change-notification.md - Load when making edits observable, batching, or recomputing derived data
• Read references/undo-redo.md - Load when adding transactional edits, undo journals, or redo stacks
• Read references/serialization.md - Load when saving/loading, versioning the format, or migrating old files
• Read references/snapshots-and-threading.md - Load when giving reader threads a consistent view while writers mutate