Special Values

To as great an extent as possible Babase utilizes a controlled vocabulary within the system's data store. Again, as far as is possible, this vocabulary may be tailored by adding or deleting codes to tables that define the vocabulary used elsewhere.[23]

At times, the Babase system recognizes that particular codes have special meanings, for example, the BIOGRAPH table's F (female) Sex code or the 0 (alive) Status code. The meaning of these codes is fixed into the logic of the system. As examples, an individual must be female to be allowed to have a menstruation, or, the individual must be alive if a sexual cycle event is to post-date the individual's Statdate. Some of these codes, like sex, are not defined in tables, they are hardcoded into the system. Others are defined in support or other tables. Because these codes have intrinsic meaning, they cannot be removed from the Babase system nor should their presence in the data be used to code a different meaning from that which the code presently has. For example, the meaning of STATUSES code value 0 should not be changed to mean death due to meteorite impact because the system's programs would then allow dead individuals to have sexual cycles. Each of the special values that the system requires retain particular meaning is listed in the Special Values section of the table's documentation. For further information on the meaning of the special values, see the description of the data table(s) that contain the code values. Should the meaning of one of these special values need to be changed, the logic in the Babase programs should be adjusted to reflect the change.

Babase prevents ordinary users from altering rows that contain special values in an attempt to prevent mis-configuration of the system. Only users with permissions to modify a table's triggers may alter the table's special values. This is not a panacea. To return to the example above, not only does the system expect a STATUSES code of 0 to mean alive, it also expects 0 to be the only code on STATUSES that means alive. If another STATUSES code is created to indicate a more specific sort of alive-ness, unless re-programmed the system will consider all individuals given that code to be dead, not alive. A careful review of the documentation should be undertaken before modifying the content of tables that instantiate special values.

[23] Examples may be readily found in the Chapter: “Support Tables.

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