In a(n) _____ diagram, the arrows above the attributes indicate all desirable dependencies.

Question

BlackTom AI · Accepted Answer

The correct answer is "dependency" because the diagram that uses arrows above attributes to show which attributes determine others is called a dependency diagram (or dependency chart) and it explicitly records the functional dependencies in a relation.

Relevant concepts:
- Functional dependency: In a relation, attribute X functionally determines attribute Y (written X → Y) if each X value is associated with exactly one Y value.
- Dependency diagram: A visual tool that places attributes and draws arrows (usually above attributes) to indicate functional dependencies among them. It is commonly used when performing normalization to identify desirable (intentional) and undesirable (redundant or transitive) dependencies.

Step-by-step reasoning and example:
1. Suppose a relation R with attributes {A, B, C, D}. If A → B and B → C, draw arrows from A to B and from B to C above the attribute list: A → B → C.
2. From these arrows we can read off dependencies: A → B, B → C, and by transitivity A → C. These are the dependencies captured by the diagram.
3. During normalization, the dependency diagram helps identify which dependencies are desirable (those that reflect true business rules and should be preserved) and which are undesirable (e.g., partial or transitive dependencies that cause redundancy).
4. The notation of arrows above attributes is characteristic: each arrow corresponds to a functional dependency and together they list "all desirable dependencies" to keep in the normalized schema.

Why the other diagram types are incorrect:
- Entity-Relationship (ER) diagrams depict entities, relationships and cardinalities between entity sets, not attribute-level functional dependencies with arrows above attributes.
- Class diagrams or hierarchy diagrams show structure and inheritance, not the functional dependencies used for normalization.
- Attribute lists without arrows don’t convey dependency direction; only a dependency diagram uses arrows to indicate determinant → dependent.

Therefore, the diagram described is a dependency diagram. This matches the provided answer: "dependency."

In a(n) _____ diagram, the arrows above the attributes indicate all desirable dependencies.单项选择题

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