What are the two options XDK and XML in DBA_REGISTRY anyway?

What are the two options XDK and XML in DBA_REGISTRY anyway?

You see them amongst other components in the DBA_REGISTRY view:

select comp_id,comp_name, version,status from dba_registry;

COMP_ID       COMP_NAME          VERSION        STATUS
-------------------- ---------------------------------------- ------------------------------ --------------------
XDB       Oracle XML Database        12.1.0.2.0       VALID
XML       Oracle XDK          12.1.0.2.0       VALID

So what are they, and how are they connected?

The XDK documentation states:

"Oracle XML Developer's Kit (XDK) is a versatile set of components that enables you to build and deploy C, C++, and Java software programs that process Extensible Markup Language (XML)."

In other words, XDK is a toolbox for developers of XML-driven applications.

The XML DB documentation states:
"Oracle XML DB is a set of Oracle Database technologies related to high-performance handling of XML data...Oracle XML DB and the XMLType abstract data type make Oracle Database XML-aware. Storing XML data as an XMLType column or table lets the database perform XML-specific operations on the content."

In other words, XML DB is the framework for allowing XML to be stored and retrieved in the database. It has been a part of the Oracle RDBMS since version 9.2.

The XDK

"supports Oracle XML DB, which is a set of technologies used for storing and processing XML in Oracle Database."

With XDK and XML DB you can

"build applications that run in Oracle Database. You can also use XDK independently of Oracle XML DB.
XDK is fully supported by Oracle and comes with a commercial redistribution license. The standard installation of Oracle Database includes XDK."