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Metadata repositories

A metadata repository is a store of metadata. A metadata repository that supports the open metadata repository standards defined by the Open Metadata Repository Services (OMRS) is called an "open metadata repository".

Home metadata repositories

The metadata repository where a metadata entity or relationship is created is called its home repository.

Metadata can only be updated and deleted in its home repository

The Open Metadata Repository Services (OMRS) is responsible for sharing this metadata with other metadata repositories who are members of the same cohort.

Reference copies

These shared copies are called reference copies.

Reference copies are read-only

Update requests to a reference copy are automatically redirected to the home repository by the OMRS, without the caller being aware.

Every metadata repository in a cohort has a unique identifier called the local metadata collection id. This identifier is set up in the server configuration and shared when this server connects to a cohort.

When metadata is shared by OMRS, each element is tagged with the metadata collection id of its home repository. OMRS is able to route update requests to the right server by comparing the metadata collection id in the metadata instance with the cohort registration information passed between members of the cohort when they connect.

Metadata collections

A metadata collection refers to a set of metadata instances that are being maintained and accessed as a coherent set of information. These instances are explicitly typed using open metadata type definitions (TypeDefs).

Typically, metadata collections are stored in a single metadata repository. However, the Open Metadata Access Services (OMASs) provide access to a federated metadata collection called the enterprise metadata collection.

Enterprise metadata collection

The enterprise metadata collection is the metadata collection that is the combination of metadata from all metadata collections held by the open metadata repositories that are members of the same open metadata repository cohorts as the server where the enterprise repository services are enabled.

Metadata collection ID

Every metadata repository has a unique identifier called the local-metadata-collection-id. This identifier is assigned automatically during the configuration of the local repository but can be overridden through administrative commands.

A new local metadata collection id is assigned when the local repository is set up

In the following server configuration, the local metadata collection id is 1b96495f-82d3-4224-9fdd-31bcb84c224c.

Local metadata collection id in server configuration

It also appears in an audit log message written at start up.

OMRS-AUDIT-0001 The Open Metadata Repository Services (OMRS) is initializing
        :                                 :                              :
OMRS-AUDIT-0003 The local repository is initializing with metadata collection id 1b96495f-82d3-4224-9fdd-31bcb84c224c

If the server is connected to a cohort, the local cohort registry sends the local metadata collection id and a registration event like the following:

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{
  "localRegistration": {
    "metadataCollectionId": "1b96495f-82d3-4224-9fdd-31bcb84c224c",
    "serverName": "cocoMDS1",
    "serverType": "Open Metadata and Governance Server",
    "registrationTime": 1531820378765,
    "repositoryConnection": {
      "class": "Connection",
      "type": {
        "type": "ElementType",
        "elementTypeId": "114e9f8f-5ff3-4c32-bd37-a7eb42712253",
        "elementTypeName": "Connection",
        "elementTypeVersion": 1,
        "elementTypeDescription": "A set of properties to identify and configure a connector instance.",
        "elementOrigin": "CONFIGURATION"
      },
      "guid": "858be98b-49d2-4ccf-9b23-01085a5f473f",
      "qualifiedName": "DefaultRepositoryRESTAPI.Connection.cocoMDS1",
      "name": "DefaultRepositoryRESTAPI.Connection.cocoMDS1",
      "description": "OMRS default repository REST API connection.",
      "connectorType": {
        "type": {
          "type": "ElementType",
          "elementTypeId": "954421eb-33a6-462d-a8ca-b5709a1bd0d4",
          "elementTypeName": "ConnectorType",
          "elementTypeVersion": 1,
          "elementTypeDescription": "A set of properties describing a type of connector.",
          "elementOrigin": "CONFIGURATION"
        },
        "guid": "64e67923-8190-45ea-8f96-39320d638c02",
        "qualifiedName": "DefaultRepositoryRESTAPI.ConnectorType.cocoMDS1",
        "name": "DefaultRepositoryRESTAPI.ConnectorType.cocoMDS1",
        "description": "OMRS default repository REST API connector type.",
        "connectorProviderClassName": "org.odpi.openmetadata.adapters.repositoryservices.rest.repositoryconnector.OMRSRESTRepositoryConnectorProvider"
      },
      "endpoint": {
        "type": {
          "type": "ElementType",
          "elementTypeId": "dbc20663-d705-4ff0-8424-80c262c6b8e7",
          "elementTypeName": "Endpoint",
          "elementTypeVersion": 1,
          "elementTypeDescription": "Description of the network address and related information needed to call a software service.",
          "elementOrigin": "CONFIGURATION"
        },
        "guid": "cee85898-43aa-4af5-9bbd-2bed809d1acb",
        "qualifiedName": "DefaultRepositoryRESTAPI.Endpoint.cocoMDS1",
        "name": "DefaultRepositoryRESTAPI.Endpoint.cocoMDS1",
        "description": "OMRS default repository REST API endpoint.",
        "address": "https://localhost:9443/openmetadata/repositoryservices/"
      }
    }
  }
}
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