Dependency Preservation in Practice
Dependency preservation matters when a relation is split into smaller relations. A design may remove update anomalies. Yet it should still allow important rules to be checked without joining every table. This calculator studies that issue with functional dependencies and decomposition schemas.
What the Tool Checks
The tool compares the original dependency set with the dependencies that can be enforced inside each decomposed relation. It first parses attributes, left sides, right sides, and relation fragments. It then computes closures. A closure shows every attribute that follows from a chosen attribute set. If every original rule can be derived from projected rules, the decomposition is dependency preserving.
Why This Is Useful
Normalization often creates cleaner tables. It can also move related attributes apart. When a rule crosses several fragments, a database may need joins to validate it. That can slow validation and complicate constraints. A dependency preservation check warns you before that design reaches production.
Advanced Review Details
The report includes a canonical cover, projected dependency summaries, and per rule closure results. The canonical cover removes repeated or redundant rules. Projection summaries show which rules belong to each decomposed schema. The per rule test explains whether each dependency is preserved or missing. This makes the result easier to audit.
How to Read Results
A preserved result means the right side of a dependency appears in the closure of its left side under the projected rules. A missing result means at least one right side attribute could not be inferred. Review those missing rules carefully. You may need another fragment, a different decomposition, or an added constraint.
Design Advice
Use small attribute names for quick experiments, such as A, B, C, and D. Use comma separated names for real schemas. Test both the proposed design and close alternatives. A dependency preserving design is not always lossless, and a lossless design is not always dependency preserving. Treat this report as one normalization checkpoint, not the whole design decision.
Keep examples realistic. Include every rule used by application logic, reports, and data entry screens. A rule that looks minor can become costly after decomposition. Save the CSV or document report when you compare versions. It helps reviewers follow schema change.