In case you didn’t already know this: Woo uses a hybrid quasi-relational / EVA NoSQL data model. It is implemented on top of WP’s underlying, equally non-relational meta schema, which runs atop MySQL or MariaDB.
The WP data model was designed initially to provide data persistence to an early CMS system. It allowed the addition of n-number of attributes to a post entity type, as needs evolved.
At its core, the WP data model consists of rows in a centrally important table that can be joined via a SELECT statement to a vertically structured (i.e., “thin”) table which specifies whatever attributes (instantiated as rows) WP would need, as time went by, for its post and, later, page types.
This has performance implications.
Also, partly because of WP’s flexible,”meta” structure, Woo does not make “normal” usage of Primary and Foreign relationships — business rules are implemented via PHP code. This leads to maintainability issues.
Moreover, Woo uses serialization, which makes its db non portable and violates the relational model’s scalar rule.