In The Third Manifesto, Date and Darwen propose a database language that:
- Is truly relational;
- Provides certain desirable programming language features, including some that are typically (but not exclusively) found under the “Object Oriented” heading;
- Represents a “firm foundation for the future of data.”
Date and Darwen have expanded these underlying principles into a collection of specific prescriptions and proscriptions. A language that conforms to these is said to be an implementation of “D”. Since the prescriptions and proscriptions are not syntactic, there may be many different language implementations that qualify as “D”.
The Third Manifesto provides a detailed specification of a specific “D” called “Tutorial D,” which is intended primarily for illustration and education. Its definition, and its application as an illustrative tool, form a core component of The Third Manifesto and a significant portion Date’s popular text, “An Introduction to Database Systems.”
To the knowledge of this author, at the time of this writing there are no complete open source Tutorial D language implementations. That includes Rel! However, the implementation described here does provide a significant and usable subset of the definition, and so it is deemed worthy of distribution, under the “release early, release often” principle of open source development.