# Topic

This schema defines the Topic entity. A topic is a feed into which message are published to by publishers and read from by consumers in a messaging service.

**$id:**[**https://open-metadata.org/schema/entity/data/topic.json**](https://open-metadata.org/schema/entity/data/topic.json)

Type: `object`

## Properties
- **id** `required`
  - Unique identifier that identifies this topic instance.
  - $ref: [../../type/basic.json#/definitions/uuid](../types/basic.md#uuid)
- **name** `required`
  - Name that identifies the topic.
  - $ref: [#/definitions/topicName](#topicname)
- **fullyQualifiedName**
  - Name that uniquely identifies a topic in the format 'messagingServiceName.topicName'.
  - Type: `string`
- **displayName**
  - Display Name that identifies this topic. It could be title or label from the source services.
  - Type: `string`
- **description**
  - Description of the topic instance.
  - Type: `string`
- **version**
  - Metadata version of the entity.
  - $ref: [../../type/entityHistory.json#/definitions/entityVersion](../types/entityhistory.md#entityversion)
- **updatedAt**
  - Last update time corresponding to the new version of the entity.
  - $ref: [../../type/basic.json#/definitions/dateTime](../types/basic.md#datetime)
- **updatedBy**
  - User who made the update.
  - Type: `string`
- **service** `required`
  - Link to the messaging cluster/service where this topic is hosted in.
  - $ref: [../../type/entityReference.json](../types/entityreference.md)
- **partitions** `required`
  - Number of partitions into which the topic is divided.
  - Type: `integer`
  - Range:  ≥ 1
- **schemaText**
  - Schema used for message serialization. Optional as some topics may not have associated schemas.
  - Type: `string`
- **schemaType**
  - Schema used for message serialization.
  - $ref: [#/definitions/schemaType](#schematype)
- **cleanupPolicies**
  - Topic clean up policies. For Kafka - `cleanup.policy` configuration.
  - Type: `array`
    - **Items**
    - $ref: [#/definitions/cleanupPolicy](#cleanuppolicy)
- **retentionTime**
  - Retention time in milliseconds. For Kafka - `retention.ms` configuration.
  - Type: `number`
- **replicationFactor**
  - Replication Factor in integer (more than 1).
  - Type: `integer`
- **maximumMessageSize**
  - Maximum message size in bytes. For Kafka - `max.message.bytes` configuration.
  - Type: `integer`
- **minimumInSyncReplicas**
  - Minimum number replicas in sync to control durability. For Kafka - `min.insync.replicas` configuration.
  - Type: `integer`
- **retentionSize**
  - Maximum size of a partition in bytes before old data is discarded. For Kafka - `retention.bytes` configuration.
  - Type: `number`
  - Default: _"-1"_
- **owner**
  - Owner of this topic.
  - $ref: [../../type/entityReference.json](../types/entityreference.md)
- **followers**
  - Followers of this table.
  - $ref: [../../type/entityReference.json#/definitions/entityReferenceList](../types/entityreference.md#entityreferencelist)
- **tags**
  - Tags for this table.
  - Type: `array`
    - **Items**
    - $ref: [../../type/tagLabel.json](../types/taglabel.md)
- **href**
  - Link to the resource corresponding to this entity.
  - $ref: [../../type/basic.json#/definitions/href](../types/basic.md#href)
- **changeDescription**
  - Change that lead to this version of the entity.
  - $ref: [../../type/entityHistory.json#/definitions/changeDescription](../types/entityhistory.md#changedescription)

## Type definitions in this schema

### topicName

- Name that identifies a topic.
- Type: `string`
- The value must match this pattern: `^[^.]*$`
- Length: between 1 and 64

### schemaType

- Schema type used for the message.
- The value is restricted to the following: 
  1. _"Avro"_
  2. _"Protobuf"_
  3. _"JSON"_
  4. _"Other"_

### cleanupPolicy

- Topic clean up policy. For Kafka - `cleanup.policy` configuration.
- The value is restricted to the following: 
  1. _"delete"_
  2. _"compact"_

_This document was updated on: Monday, November 15, 2021_