You may get some insight by comparing Ada's tagged type, examined in Ada 95 Rationale: II.1 Programming by Extension, with Oberon-2's type tag, discussed in Object-Oriented Programming in Oberon-2: Run-Time Data Structures, cited here. Both use a record structure with hidden type information to implement inheritance and polymorphism. See also A Comparison of the Object-Oriented Features of Ada 95 and Java, cited here.
Addendum: So are they simply associating procedures with records?
An Oberon record type encapsulates both procedures and data, in a manner similar to the object type in Object Pascal. An Ada tagged record encapsulates the data, while the enclosing package encapsulates the subprograms and record.