Object-oriented query languages: the notion and the issues
Elisa Bertino, Mauro Negri, Giuseppe Pelagatti, Licia Sbattella · IEEE Transactions on Knowledge and Data Engineering · 1992
The authors describe how the characteristics of an object-oriented data model, such as object identity, complex object structure, methods, and class hierarchies, have an impact on the design of a query language. They also point out major differences with respect to relational query languages. The discussion is supported through the definition of OOPC, a formal object-oriented query language based on predicate calculus, which incorporates in a consistent formal notation most features of existing object-oriented query languages.>