The COCOON model was intended to extend the concepts of relational database management systems (DBMSs) beyond nested relational to object-oriented ones. Key characteristics of COCOON and its database language COOL are: generic, set-oriented query and update operators similar to relational algebra and SQL updates, respectively; object-preserving semantics of query operators, which allows for the definition of updatable views; update operations that keep model-inherent integrity constraints consistent; a separation of the two aspects of programming language "classes": type vs. collection; predicative description of collections, similar to "defined concepts" in KL-One-like knowledge representation languages; automatic classification of objects and views (positioning in the class hierarchy). This report gives a comprehensive introduction to the COCOON model and its language COOL as well as a formal de nition. Our formalization uses denotational semantics, a popular technique in programming languages. We found that standard set-theoretic formalizations of data and object models were not equally well-suited to express update semantics. This, however, is essential for object-oriented as opposed to value-based languages. This can also be taken as an indication for the convergence of database languages to generell programming languages. Along these same lines, we emphasized static-type checking of COOL.

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