Chapter 4 Building Conceptual Data Models
A specifying entity attribute is an entity attribute that is defined for a parent entity which differentiates occurrences of each child. It only applies to parent only generation.
In the example below, the TITLE entity has two children, NONPERIODICAL and PERIODICAL.
As only the parent table TITLE will be generated in a PDM, a specifying entity attribute PERIODICAL is defined for the inheritance link to differentiate between the two child entities.
In the PDM, each of the child entity attributes will generate columns in the table TITLE, however the specifying entity attribute PERIODICAL will generate a corresponding column PERIODICAL. The values of this column indicate whether an instance of TITLE is a periodical or not.
You can specify the following properties for a specifying entity attribute:
| Property | Description |
|---|---|
| Name | The name of the item which should be clear and meaningful, and should convey the item's purpose to non-technical users |
| Code | The technical name of the item used for generating code or scripts, which may be abbreviated, and should not generally include spaces |
| Comment | Descriptive label for the specifying entity attribute |
| Data type | Data type that you want to apply to the specifying entity attribute |
| Length | Maximum length of the data type |
| Precision | Number of places after the decimal point, for data values that can take a decimal point |
| Domain | Name of the associated domain |
| Mandatory | Indicates whether or not the specifying entity attribute must be assigned a value |
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