Is Sesame a "relational" database?

Yes. Sesame supports two kinds of relational data. By default, and with very little effort on the part of the developer, Sesame supports a one-to-many hierarchial relationship. That means, that without much effort you can set up an invoice form that has a line item table, with entries unique to the customer on each invoice. Sesame also supports (without much more effort) a "keyed" relationship between a form and subform, where one field on the subform must match a field on the parent form. Forms can be nested as deeply as necessary.

Sesame also supports the same kinds of relationships as Q&A, through the use of XLookup and related SBasic functions.