The characteristic of relational operation is that the operation object and operation result are both sets, while the data operation method of the non-relational data model is one record at a time. Relational data algebra languages, relational calculus languages, and languages that feature both relational algebra and relational calculus (eg, SQL). Relational calculus languages include tuple relational calculus languages (eg Aplha, Quel) and domain relational calculus languages (eg QBE).
Relational algebra language, tuple relational calculus and domain relational calculus are abstract query languages, which are not the same as the actual languages implemented in concrete DBMSs.