# Need help understanding the tuple relational calculus

We say that a query in a TRC is a statement of the form $$\{T: P(T)\}$$, where $$T$$ is a tuple variable and $$P(T)$$ is a formula.

Now my question is, what are the possible tuples $$T$$ to be tested i.e., what are the types and values for tested tuples.

As far as I know in set theory and in particular in set builder notation the variables should come from another well-defined set.

A tuple is of the form $$T=(D,R,h)$$ where $$D$$ is the domain, $$R$$ is a set of relation names, and $$h$$ is a mapping that associates a column name to each relation in $$R$$. To represent a tuple, we can see $$D$$ as the set of keys, and $$R$$ the table associated with those set of keys, and $$h$$ the column names of the table.