This document discusses biological databases and their classifications. It introduces bioinformatics and the need for biological databases to store and communicate large datasets. It describes different types of biological data that can be stored in databases, including nucleotide sequences, protein sequences, 3D protein structures, and gene expression data. The document also covers different ways databases can be classified, such as by the type of data, whether they contain primary or analyzed data, how the data is linked, and access restrictions.