Guidelines for Using G2
The G2 data language was designed to provide an efficient but change-tolerant
coupling between compiled programs.
With care, a fair amount of inconsistency can
be tolerated among a set of communicating processes.
This should allow program developers
to be more effective in a less than consistent environment.
When a record is passed between programs using G2 some useful interpretations
take place:
-
Only non-empty fields and their attendant hierarchy are transmitted;
non-transmitted fields are seen by the receiver as empty strings.
This provides
a form of data compression while
relieving the transmitter of having to meet the
expectations of the receiver(s).
-
Receivers discard unknown fields. This means that a transmitter
may enrich a G2 record with out affecting its receivers.
The receivers may upgrade
to the enriched records as convenient.
-
Receivers truncate lengthy fields.
This preserves the integrity of
C data structures.
-
Transmitters send only printable (isprint(3))
data.
Receivers accept only printable data.
Strings are terminated by the first
non-printable byte.
Thus, the communications link is filtered at both ends.
With the above mechanisms in mind here are some serviceable
guidelines for using G2 records.
-
Be generous in defining the maximum length of G2 fields. Since only
non-empty strings are transmitted,
the cost of defining larger G2 records is mainly
in the size of the C data structure allocated within the program.
These buffers
are usually few in number, so one can
afford to relax a bit about their size.
It is better to have a larger G2 definition
than needed than to ``creep'' the definition.
For example, one should specify a numeric
field at least 11 bytes long (long enough
to represent, in ASCII, the biggest negative integer on a 32 bit machine).
-
Be miserly in defining G2 names; use the structuring facilities of
G2 to create scopes where short names are distinctive.
The root name of a G2 record
becomes an external symbol so it should be kept to 6 characters.
Also, since most
UNIX output devices have tabs set every eight spaces,
G2 records are easier to read
raw when field names are less than 7 characters long.
-
Never change the meaning of a name; rather, invent a new one and
gracefully retire the old one.
This may mean supporting redundant data fields until
other programs in a system have time to conform to new schemes.
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Interpreted Interface
© 2004 The SCO Group, Inc. All rights reserved.
UnixWare 7 Release 7.1.4 - 27 April 2004