Well, anyone can pick up the definition of relational model by Googling and reading the Wikipedia page on this. What I want to point out, based on my experience, is that relational model is a clean way to sort out concepts around data in an enterprise situation. There have been other types of models in the database theory, such as hierarchy and network models. Relational models fit the need of OLTP system design quite perfectly and have been the dominant modelling method for more than 40 years. Right now, there are object oriented models, and other variations of relational models exist in the industry.
One of the key challenges to the relational modelling, is that the management of history inside a model. In the relational theory, the 1NF (Normal Form), 2NF, to BCNF,4NF, and 5NF are even not enough to keep historical data in a clean way. People have introduced 6NF to manage history data in relational theory.
The key concepts in relational modelling are, for example, entity, entityset, relationship, relationshipset, one-to-many, many-to-many, one-to-one relationships, etc. So, how does people in the enterprise world understand a data model? Diagrams, yes, the diagrams. Most people could not understand the modelling tools such as IDA, RSM, WBM, until they see the diagrams shown in the tool. Diagrams are the key output in a modelling session.
So, improve your "diagramming" skill if you plan to be a modeller :)
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