Predefined schema is very powerful mechanism that can reduce a lot reading/writing datasets, but in order to make it even more usable we should allow to save/read schema from associative arrays which can be turned into json/xml/yaml/whatver.

Two things are a bit problematic here, but I think we can simplify them.

• Constraints - this mechanism was pretty much replaced by introducing types so I think we can safely remove Schema Definition Constraints
• Metadata - I would keep metadata but I would remove possibility of putting objects into it.

That should give us following API:

Schema::toArray() : array
Schema::fromArray() : array

Which can be later used to create:

• schema_from_json(string $schema) : Schema
• schema_to_json(Schema $schema) : string