An SQL-based query language for networks of relations
Amit Ranjan Basu, Rafiul Ahad · ACM SIGMOD Record · 1990
A set of relations can be modeled as a network through the use of image attributes , which are attributes defined on the domain of relation names. Such networks of relations can effectively meet many of the modeling requirements of advanced database applications such as engineering design and knowledge base systems. In this paper, we describe the features of ESQL, a novel query language that is an extension of SQL [Cham74] to exploit the added semantics of image attributes. Details of ESQL and its underlying principles can be found in [Ahad88] and [Ahad89].