"Can you have 2 tables
with identical structure in a good DB schema (item_id, user_id, time). Some of the records will be identical but their meaning will be different depending on which table they are in. The "views" table is updated any time a user views an item for the first time. The "downloads" table is updated any time a user downloads an item for the first time. Both of the tables can exist without the other.
"I don't think that there is a problem, per se from a E/R modelling point of view, as long as they represent two semantically different entities."
"Are you saying that both tables have an 'item_id' Primary Key? In this case, the fields have the same name, but do not have the same meaning. One is a 'view_id', and the other one is a 'download_id'. You should rename your fields consequently to avoid this kind of misunderstanding."
"Chris Date and Dave McGoveran formalised the Principle of Orthogonal Design. Roughly speaking it means that in database design you should avoid the possibility of allowing the same tuple in two different relvars. The aim being to avoid certain types of redundancy and ambiguity that could result."
"When designing a DB there are lots of different parameters, and some (e.g.: performance) may take precedence. Case in point: even if the structures (and I suppose indexing) are identical, maybe "views" has more records and will be accessed more often. This alone could be a good reason not to burden it with records from the downloads."
--Can you have 2 tables with identical structure in a good DB schema?, StackOverflow.com