Datum extensions and references
The Tcl datum extensions perform operations on a message fragment, known as a datum. Datum extension objects associate a system-supported data type with arbitrary data. They are most often used in conjunction with GRM and XPM handles. See GRM extensions and XPM extensions.
Datum (DAT) objects are the smallest unit of data available in a given record format. For example, in FRL, a datum represents a subfield; in HL7, it represents a subcomponent.
Datum objects have two attributes:
VALUE
TYPE
: The type specifies the nature of the value. It is particularly useful for parsing and converting date and time values. A datum's type must be a legal hci datatype. : A datum's value is the characters or number the datum represents.
Although the type value must be a legal datatype, no type checking is performed against the value. It is therefore up to the user to ensure a datatype value matches its type. Unexpected recalls can happen with mismatched types and values.
This section gives a brief overview of the commands that permit manipulation of datum (DAT) objects. Datum objects are most useful when used in conjunction with other hci extensions. Datum objects are included in examples. See GRM extensions and XPM extensions.
Datum objects represent empty values as empty value strings. They represent active null values with a type value of null. Record formats use and identify active null values differently.