Your question seem to be a bit confusing because it lacks descriptive database type information. For instance, in your question referencing the 50-80 tables in a database with relationships among some of the tables, you don't say whether it is a RDBMS (Relational Database Management System) or not. Without knowing the database type, the collection of tables could well be a Data Warehouse using a "Star" or "Snowflake" -Type schema. If that is the case, your questions would be null and void.
Outside of that, my following comments are based on the the definitions on page 10 of Chapter 1, Review of Terminology in the Beginning ASP.NET 2.0 and Databases. Review the definition of a DataSet, Data store and Database or RDBMS. Then turn to page 16 and review the section on "Nonrelational Stores of Data". A database, whether it is Nonrelational or Relational is a DataSet. So your Project may have multiple DataSets, based on project requirements.
A Relational Database consists of multiple tables and this collection of tables and their data is 1 DataSet. A Nonrelational Database is a data-file(data store) and 1 DataSet. An example of this type of database and data-file is an XL-file(Excel) and 1 DataSet. However an XL-Workbook, which consists of multiple XL-spreadsheets is still 1 DataSet.
Hope this helps.
Disclaimer: The above comments are solely the opinion of one person and not to be construed as a directive or an incentive to commit fraudulent acts.