You can use elementary field names, virtual field names, and
group field names as value expressions.
1 – Elementary and REDEFINES Field Names
The value specified by an elementary field name is the value
stored in a field of a record. If the field name you use refers
to a REDEFINES field, the value associated with the name is
determined by the clauses that define the REDEFINES field in
the record definition.
2 – COMPUTED BY Fields
COMPUTED BY fields are virtual fields. DEC DATATRIEVE does not
store the value of a COMPUTED BY field in a record. That value
is calculated every time you refer explicitly or implicitly to a
COMPUTED BY field.
The COMPUTED BY clause includes a value expression. The value
specified by the virtual field is associated with the value
expression in the COMPUTED BY clause.
3 – Group Field Names
When you use group field names in assignment statements, the
value of the group field depends on the type of assignment you
specify. For example:
o group-field-name-1 = group-field-name-2
In this type of assignment, the value of group-field-name-2
includes the values of all elementary fields, all REDEFINES
fields, and all COMPUTED BY fields. The assignment of values
is made on the basis of similar field names. For field
names in group-field-1 that match names in group-field-2,
DEC DATATRIEVE assigns the values in group-field-2 to the
appropriate fields in group-field-1.
DEC DATATRIEVE ignores any fields in group-field-2 whose
names do not match any field names in group-field-1. For any
elementary field in group-field-1 whose name matches none of
the field names in group-field-2, DEC DATATRIEVE assigns the
MISSING or DEFAULT value if one is defined for the field, or a
value of 0 if the field is numeric, or a blank if the field is
alphabetic or alphanumeric.
DEC DATATRIEVE stores no values in any COMPUTED BY or
REDEFINES fields in group-field-1, regardless of any matches
between the names of those fields and fields of any type in
group-field-2.
The values of the elementary, REDEFINES, and COMPUTED BY
fields associated with group-field-name-2 are the values
stored in or associated with the fields that constitute group-
field-2 of a record.
o elementary-field-name = group-field-name
Because of problems that can arise from conflicting data
types, assignments of this type are not recommended.
If you make an assignment of this type, the value of the group
field is the same value displayed when you enter a DISPLAY
group-field-name statement. The value is the concatenation of
the values in the elementary fields that constitute the group
field. The REDEFINES and COMPUTED BY fields are ignored. You
can reduce conflicts of data types by using an alphanumeric
PICTURE string in the definition of the elementary field.
4 – Query Names
If the record definition contains a query name for a field, you
can use the query name exactly as you use the associated field
name.
5 – Qualifying Field Names
To clarify the context for recognizing names and associating
values with those names, you can qualify field names with several
optional elements:
o Context variables
Distinguish between fields in different record streams.
o Collection names
Distinguish between fields in selected records in different
collections. You can use a collection name to modify a field
from a selected record only.
o Domain names
Distinguish between fields that have the same field name but
are associated with different domains.
o Record names
Distinguish between fields that have the same field name but
are contained in different records.
o Group field names
Distinguish between fields that have the same field name but
are contained in different group fields.
Use the following format to specify field names:
[ collection-name ]
[ context-variable ][domain-name] [group-field-name] [...] field-
[ ]
name
For duplicate field names, you must specify whatever option or
combination of options is needed to make the name unique.