SQLAlchemy core includes SQL rendering engine, DBAPI integration, transaction integration, and schema description services. SQLAlchemy core uses SQL Expression Language that provides a schema-centric usage paradigm whereas SQLAlchemy ORM is a domain-centric mode of usage.

The SQL Expression Language presents a system of representing relational database structures and expressions using Python constructs. It presents a system of representing the primitive constructs of the relational database directly without opinion, which is in contrast to ORM that presents a high level and abstracted pattern of usage, which itself is an example of applied usage of the Expression Language.

Expression Language is one of the core components of SQLAlchemy. It allows the programmer to specify SQL statements in Python code and use it directly in more complex queries. Expression language is independent of backend and comprehensively covers every aspect of raw SQL. It is closer to raw SQL than any other component in SQLAlchemy.

Expression Language represents the primitive constructs of the relational database directly. Because the ORM is based on top of Expression language, a typical Python database application may have overlapped use of both. The application may use expression language alone, though it has to define its own system of translating application concepts into individual database queries.

Statements of Expression language will be translated into corresponding raw SQL queries by SQLAlchemy engine. We shall now learn how to create the engine and execute various SQL queries with its help.