Subtype indicators

For each subtype table you define, USoft automatically creates a subtype indicator column in the supertype table. A subtype indicator is a Yes/No flag that indicates, for each subtype, if a given supertype instance (a supertype record) is also of the subtype.

Physically, a subtype indicator is a database column storing 'Y' and 'N' values.

Subtype indicators are used in USoft's GUI implementation of subtypes.

Example

You define 2 subtypes of PERSON:

Table Name	Supertype
GUIDE	PERSON
STAFF	PERSON

As a result, the PERSON table will contain 2 subtype indicators. Here is an example record for a person called SMITH who is a guide, but not a member of staff:

Columns in table PERSON	Example values
PERSON_ID	884
NAME	SMITH
...	...
GUIDE	Y
STAFF	N

Tips for good design

USoft automatically creates each subtype indicator as a column based on the USoft-shipped default domain = TW_YESNO. This domain, by default, has Default Value = N.

•Keep the TW_YESNO domain for each subtype indicator.

•Do not use the TW_YESNO domain for application-specific columns (columns that you define yourself).

•Do not change the Default Value: keep Default Value = N at the level of the TW_YESNO domain, and do not specify any Default Value at column level.