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The Adapter integration pattern enables existing metadata repositories and tool sets to integrate into the open metadata ecosystem.  It requires the development of simple components that map between the proprietary metadata formats and the open metadata formats plus manage notifications around the activity occurring with the metadata repository.

A metadata repository needs the following capabilities to support the adapter pattern:

• A remotely callable interface (API) that allows metadata to be queried, created, updated and deleted.
• The generation of event notifications whenever metadata changes in the metadata repository.

The API is wrapped in an OMRS Connector implementation that maps open metadata repository service calls to the API of the metadata repository.   The event notifications are captured and mapped into the OMRS Events by an Event Mapper.  The Event Mapper published the resulting OMRS Events to the other metadata repositories in the cluster.

Figure 1 shows the adapter pattern in operation for a fictitious metadata product called XYZ.  Its OMRS Connector and Event Mapper are running in a Repository Proxy.  The repository proxy manages the OMRS Connector and Event Mapper and ensures they are called at appropriate times.

Figure 1: High level operation of the adapter pattern

Figure 3: Different XYZ OMRS Connector deployment choices

• A - The OMASs are configured to talk directly to the XYZ OMRS Connector.  This means all of the metadata requests flow to XYZ.
• B - This is the same pattern shown in figure 2.
• C - In this option, the XYZ OMRS Connector has not been contributed to Apache Atlas and so it needs to run in an OMRS OMAG Repository Proxy that the XYZ team has constructed and deployed.  This option leaves the XYZ repository and toolkit deployment unchanged but requires two network hops to get from an OMAS API to the XYZ metadata.
• D - In this option OMRS components have been built into the XYZ product and so the XYZ metadata can be reached through the standard OMRS REST Connector.  This is the pattern that the Apache Atlas metadata repository implements - see Local Atlas OMRS Connector for more details.