# Data Formats (Serialization)

### Protocol Buffers and Descriptors

A **Descriptor** defines the data serialization format for a record’s native data format. Descriptors are defined for an entity within a [Store](https://docs.deltastream.io/overview/core-concepts/store). This provides different serialization formats for records within a store, while defining a clear schema definition for a stream of records through the store. See [Working with ProtoBuf Serialized Data and DeltaStream Descriptors](https://docs.deltastream.io/how-do-i.../serialization/working-with-protobuf-serialized-data-and-deltastream-descriptors) and [create-descriptor\_source](https://docs.deltastream.io/reference/sql-syntax/ddl/create-descriptor_source "mention") for more information on how to import and create descriptors in DeltaStream. Currently, DeltaStream uses descriptors to support data in ProtoBuf format.

### JSON

A JSON serialization format is assumed for an [entity](https://docs.deltastream.io/overview/core-concepts/store#entity), if no [schema registry](https://docs.deltastream.io/overview/core-concepts/store#schema-registry) is defined for the corresponding store and no descriptor is defined for the entity. If a schema registry is present in the store and a descriptor is defined for an entity, DeltaStream uses the descriptor to serialize that entity.

### Avro and Schema Registry <a href="#schema_registry" id="schema_registry"></a>

A [schema registry](https://docs.deltastream.io/overview/core-concepts/store#schema-registry) is a service to manage message schemas in streaming stores such as Apache Kafka. Message schemas are used to serialize and deserialize messages stored in entities. In DeltaStream, a schema registry is a representation of a schema registry service that can be used to fetch and store schemas for entities in the service. A store can use one schema registry at a time, but a schema registry can be used by multiple stores. When a schema registry is attached to a store, any entity in that store using data serialization formats requiring a schema registry will use the store’s associated schema registry to fetch the schemas/metadata necessary for marshalling and unmarshalling data events. The schema for an event, fetched by the schema registry, should not be confused with the [schema](https://docs.deltastream.io/overview/core-concepts/databases#_schema) belonging to a [database](https://docs.deltastream.io/overview/core-concepts/databases) for organizing relations.