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Open Metadata Archive

An open metadata archive is a document containing open metadata type definitions and instances.

The open metadata archive has two types:

  • A Content Pack: reusable definitions that are generally useful. They may come from the Egeria community or third parties.
  • A Metadata Export: an export of metadata from a repository. Used to transfer metadata between repositories that are not connected to the same cohort.

Structure of an open metadata archive

The logical structure of an open metadata is shown in Figure 1:

Figure 1

Figure 1: Logical Structure of an Open Metadata Archive

Figure 2 shows how the instances are linked together. Entities are stored as EntityDetail structures. Relationships are stored as Relationship structures and link to their entities through the embedded entity proxies. The entities will include their classifications. However for classifications that are attached to entities that are not included in the archive, they are stored in an ClassificationEntityExtension structure.

Figure 2

Figure 2: Instance structures in an Open Metadata Archive

Typically, open metadata archives are encoded in JSON format and stored in a file. Figure 3 show an example of the archiveProperties header from the Cloud Information Model Archive

{
  "class":"OpenMetadataArchive",
  "archiveProperties":
      {
          "class":"OpenMetadataArchiveProperties",
          "archiveGUID":"9dc75637-92a7-4926-b47b-a3d407546f89",
          "archiveName":"Cloud Information Model (CIM) glossary and concept model",
          "archiveDescription":"Data types for commerce focused cloud applications.",
          "archiveType":"CONTENT_PACK",
          "originatorName":"The Cloud Information Model",
          "originatorLicense":"Apache-2.0",
          "creationDate":1570383385107,
          "dependsOnArchives":["bce3b0a0-662a-4f87-b8dc-844078a11a6e"]
      }, 
   "archiveTypeStore":{},
   "archiveInstanceStore":{}
}

Figure 3: Example of an open metadata archive header encoded in JSON

However, both the format and storage method can be changed by changing the open metadata archive connector.

Processing Design

Open metadata archives are introduced into the server through the admin services either provided as part of the contents of the server's configuration document or through the operational command that added the archive directly into the running server's repository. These entry points are shown as (1) and (2) respectively on Figure 1.

Figure 4

Figure 4: Processing of an open metadata archive

The archive is passed to the repository services' Operational Services which in turn passes it on to the Archive Manager. Type information is passed to the Repository Content Manager. Both the Types and Instances are passed to the local repository (if there is one).

  • TypeDefs added through verifyTypeDef and then addTypeDef in the following order:
    • AttributeTypeDefs
    • New TypeDefs
    • TypeDefPatches
  • Instances loaded as reference copies in the following order:
    • Entities
    • Relationships
    • Classifications

If the server is connected to the cohort, the new content is send as notifications to the rest of the cohort.

Archive Load Order

The archive loads in the following order:

  • Attribute Type Definitions (AttributeTypeDefs) from the type store.

    • PrimitiveDefs
    • CollectionDefs
    • EnumDefs

  • New Type Definitions (TypeDefs) from the type store.

    • EntityDefs
    • RelationshipDefs
    • ClassificationDefs

  • Updates to types (TypeDefPatches)

  • New Instances

    • Entities
    • Relationships
    • Classifications

Further information

More information about open metadata archives can be found in the open-metadata-archives module.

In addition, these articles may be of interest:

License: CC BY 4.0, Copyright Contributors to the ODPi Egeria project.