Is is appropriate to consider metadata as the instance of data model?
I am sure that in relational DBMS, foreign key is part of its data model, and the specification of foreign key is kind of metadata. But I found no evidence that is instance of relationship is universal between these 2 concepts.
BTW, I've already refered some text books like Database System Concepts and Fundamentals of Database Systems.
Metadata is data that expresses a data model. An example is the data dictionary that accompanies the schema in most database systems. The advantage of this way of expressing a model is that the same query language that is used to examine the data can be used on the metadata.