| Class | IActive | It defines if a certain object can be active or not |
| Class | IContainer | An objects that holds other objects or items |
| Class | IDescribable | It defines that a object can be described through get_description |
| Class | IStorable | Storable documentation for a certain product or a sellable item. |
| Class | IPersonFacet | A facet on a Person, the only thing it has is a named reference |
| Class | IPaymentFacet | A facet on a Payment, the only thing it has is a named reference |
| Class | IIndividual | Being or characteristic of a single person, concerning one |
| Class | ICompany | An institution created to conduct business |
| Class | IClient | An individual or a company who pays for goods or services |
| Class | ISupplier | A company or an individual that produces, provides, or furnishes |
| Class | IEmployee | An individual who performs work for an employer under a verbal |
| Class | IUser | An employee which have access to one or more Stoq applications |
| Class | IBranch | An administrative division of some larger or more complex |
| Class | ISalesPerson | An employee in charge of make sales |
| Class | IBankBranch | Undocumented |
| Class | ICreditProvider | No class docstring; 1/1 methods documented |
| Class | ITransporter | An individual or company engaged in the transportation |
| Class | IInPayment | Interface specification for InPayments. |
| Class | IOutPayment | Interface specification for OutPayments. |
| Class | IPaymentTransaction | Interface specification for PaymentGroups. |
| Class | IDelivery | Specification of a Delivery interface for a sellable. |
| Class | IReversal | A financial entry which support reversal operations |