CSDP Step 2: Conceptual Schema Design Procedure

CSDP Step 2: Draw Fact Types and Populate

• CSDP Step 2 involves drawing a conceptual schema diagram that shows all the fact types, which illustrates the relevant object types, predicates, and reference schemes.
• The diagram is then checked with a sample population.
• Conceptual schema diagrams depict an entity type as a named, solid, soft rectangle (rectangle with rounded corners).
• A value type is shown as a named, broken, soft rectangle.
• Object type names are written inside the rectangle.

Instance Diagrams

• Instance diagrams illustrate particular instances of objects and relationships.
• Cartoon drawings are used to denote the actual people and cars.
• Values are shown as character strings.
• A particular fact or relationship between a person and a car is shown as a solid line.
• A particular reference between a value and an entity is shown as a broken line.

Fact Types and Population

• As a check, each fact type on the diagram is populated with some of the original fact instances.
• A fact table is added for each fact type, and the values are entered in the relevant columns of the table.
• A diagram that includes both a schema and a sample database is called a knowledge base diagram.

Examples

• The example of Table 3.6 shows three elementary facts: • The Person named ‘Adams B’ drives the Car with regNr ‘235PZN’. • The Person named ‘Jones E’ drives the Car with regNr ‘235PZN’. • The Person named ‘Jones E’ drives the Car with regNr ‘108AAQ’.
• Figure 3.8 shows an instance diagram for this example.
• Figure 3.9 shows a conceptual schema diagram for the same example, with inverse readings for the two fact types.

Roles and Value Types

• On a conceptual schema diagram, the roles (relationship parts) played by objects are shown explicitly as boxes.
• Optionally, roles may be given a name, in which case the role name is displayed in square brackets next to the role box.
• Value type names are generated from unit-based reference modes by replacing the colon by “Value” (in English).

Unary and Binary Fact Types

• Table 3.8 shows an example of unary fact types, where each fact is an instance of a different unary fact type.
• The knowledge base diagram is shown in Figure 3.12, where the two roles belong to different fact types.
• The two unaries can be transformed into a single binary by introducing another entity type, such as SmokingStatus.
• The binary version is shown in Figure 3.13.

Ring Fact Type

• A ring fact type has one entity type, where each role in a fact type is played by the same object type.
• The binary case of this is called a ring fact type, since the path from the object type through the predicate loops back to the same object type, forming a ring.
• Figure 3.14 shows an example of a ring fact type with a sample population.