APPENDIX BHIERARCHICAL AND NETWORK DATABASES
For the majority of the discussions in this book we have been considering the relational model of data, first proposed by Edgar F. Codd (1970), when talking about the way that data is structured in databases. In the relational model, data is logically stored in relations, which are sets of tuples, with each tuple being a set of attribute-value pairs. In the physical embodiment of this model, with database management systems based on the SQL database language, the data is logically considered to be stored in tables.
Although it is the most common logical construct for storing data in databases, the table is not the only logical construct. Other models of data include: