Semantic
Semantic data is data that has been structured to add meaning to the data. This is done by creating data relationships between the data entities to give truth to the data and the needed importance for data consumption. Semantic data helps with the maintenance of the data consistency relationship between the data.
Relational
Relational data uses a structure and language consistent with firstorder predicate logic,^{1} where all data is represented in terms of tuples,^{2} grouped into relations.
The purpose of the relational model is to provide a declarative method for specifying data and queries: users directly state what information the database contains and what information they want from it, and let the database management system software take care of describing data structures for storing the data and retrieval procedures for answering queries.
Footnotes

Firstorder logic—also known as firstorder predicate calculus—is a collection of formal systems used in mathematics, philosophy, linguistics, and computer science. ↩

In mathematics, a tuple is a finite sequence or ordered list of numbers or, more generally, mathematical objects, which are called the elements of the tuple. ↩