#+TITLE: Domino

* About

Domino is an *Extended Relational Database Engine* based on E. F. Codd's
RM/T (Relational Model/Tasmania, 1979). It implements relational algebra
in its strict, theoretical form while extending it to capture more of the
meaning of data through semantic modeling concepts.

** Theoretical Foundation

The engine builds upon two seminal works by E. F. Codd:

1. *"A Relational Model of Data for Large Shared Data Banks"* (1970) —
   The foundation of relational theory
2. *"Extending the Database Relational Model to Capture More Meaning"* (1979) —
   RM/T extensions for semantic modeling

** Core Principles

A relation is modeled as a set of tuples, each tuple being a set of
attributes. Each attribute is a pairing of a name with a value drawn
from a domain. All operations are defined on entire relations as sets,
with no recourse to the compromises typical of SQL or other practical
implementations.

** What Makes Domino Extended?

*** Content-Addressed Storage
Entities are identified by system-controlled *surrogates* — cryptographic
hashes (SHA-256) that provide permanent, unique identification. This
enables:
- Automatic deduplication
- Immutable versioning
- Merkle tree-based diffing
- Distributed synchronization

*** Entity Types (RM/T)
Three fundamental entity classifications:
- *Kernel Entities* — Independent entities (e.g., Employee, Supplier)
- *Characteristic Entities* — Multi-valued properties (e.g., Job History)
- *Associative Entities* — Relationships as first-class entities

*** Four Dimensions of Molecular Semantics
1. *Cartesian Aggregation* — Properties, characteristics, and associations
2. *Generalization* — Subtyping and inheritance hierarchies
3. *Cover Aggregation* — Collections and groupings (e.g., teams, convoys)
4. *Event Precedence* — Temporal ordering of events

*** Immutable Architecture
All data structures are immutable. Every modification creates a new version
with a new hash, enabling:
- Temporal queries
- Audit trails
- Safe concurrent access
- Version control for data

** Current Implementation

*** What's Built
- Content-addressed storage with SHA-256 surrogates
- E-relations for entity type management
- P-relations for immediate properties
- Merkle tree integration for efficient versioning
- Volcano iterator model for lazy evaluation
- Transactional ACID operations via Mnesia
- Comprehensive EUnit test suite

*** What's Planned
- Full relational algebra operators (σ, π, ⋈, ∪, ∩, −)
- Characteristic entities and CG-relation
- Associative entities and AG-relation
- Generalization hierarchies (UGI/AGI)
- Cover aggregation (KG-relation)
- Event precedence (US/AS/UP/AP)
- Extended operators (OUTER JOIN, MAYBE operators)
- RM/T catalog relations
- Null value handling (three-valued logic)
- Infinite relations (aleph₀)
- High-level query language

** Design Philosophy

The engine is intended as a study in correctness and semantic richness:
each operation is executed in a manner consistent with the classical
definition of relational algebra, while the RM/T extensions provide a
framework for capturing more meaning about entities, their properties,
and their relationships.

It is a platform for exploring the consequences of relational theory in
a low-level programming context, providing both a tool for experimentation
and a concrete realization of Codd's vision for semantic data modeling.

** Why RM/T?

Most database systems today are compromises — they sacrifice theoretical
purity for practical performance. Domino takes a different approach:
implement the theory *correctly* first, then optimize. RM/T provides:

- *Atomic Semantics* — What constitutes a minimal meaningful unit?
- *Molecular Semantics* — What larger clusters constitute meaningful units?
- *Systematic Design* — Principled approach to database schema design
- *Intelligent Behavior* — System understands more about data meaning

** Documentation

See =docs/= directory:
- =code.org= — Comprehensive code documentation
- =features.org= — Feature roadmap and RM/T extensions
- =ci.org= — Continuous integration setup

** References

- Codd, E. F. (1970). "A Relational Model of Data for Large Shared Data Banks."
  /Communications of the ACM/ 13(6): 377-387.
- Codd, E. F. (1979). "Extending the Database Relational Model to Capture More Meaning."
  /ACM Transactions on Database Systems/ 4(4): 397-434.
- Date, C. J. & Darwen, H. "Foundation for Future Database Systems: The Third Manifesto."

** License

See LICENSE file.