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Closed 3 years ago . I understand that the database design process occurs in the following sequence:Conceptual Data Model -> Logical Data Model -> Physical Data Model The term "data model" as originally coined has been hijacked by the industry to come to mean something completely different.
Originally, it meant "a model telling us which structures (i.e. mathematical concepts . ) we use to manage our data with (whatever those data are)". In the industry, it almost exclusively means "a model of which pieces of information are important for some business, and how those pieces of information relate to one another".
All of the three models (some more some less, but not that much) are models in the latter meaning. Which is why I personally always prefer to call them information models, not data models.
The relational model of data is a "genuine" data model in the former meaning of the term. It could be summarized in one sentence as "all information in the system is represented using only relations". Other data models (in the former sense) could, e.g., say "all information in the system is represented using only graphs consisting of nodes and edges".
So now to answer your question, the relational model "fits in" in that it offers one possible way to organize your logical information models. Starting from the same conceptual information model, you could also work out a graph-based logical information model, and it would look radically different from the one you'd get using the relational model.