Schemaless Data Structures by Martin Fowler.
From the first slide:
In recent years, there’s been an increasing amount of talk about the advantages of schemaless data. Being schemaless is one of the main reasons for interest in NoSQL databases. But there are many subtleties involved in schemalessness, both with respect to databases and in-memory data structures. These subtleties are present both in the meaning of schemaless and in the advantages and disadvantages of using a schemaless approach.
Martin points out that “schemaless” does not mean the lack of a schema but rather the lack of an explicit schema.
Sounds a great deal like the implicit subjects that topic maps have the ability to make explicit.
Is there a continuum of explicitness for any given subject/schema?
Starting from entirely implied, followed by an explicit representation, then further explication as in a data dictionary, and at some distance from the start, a subject defined as a set of properties, which are themselves defined as sets of properties, in relationships with other sets of properties.
How far you go down that road depends on your requirements.