IBM Informix - Integration Through Data Federation

ISBN : 0738491055

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Sample Chapter From IBM Informix - Integration Through Data Federation
Copyright © Chuck Ballard, Vlaunir Da Silva, Daniel M. Farrell, Alexander Koerner, Jonathan Sayles

IBM Informix 4GL

As previously stated, this IBM Redbook is primarily oriented towards business
application development using IBM EGL, and the topic of transitioning from IBM
Informix 4GL. In order to establish certain knowledge prerequisites, we review
the history, conventions, and use of the IBM Informix 4GL in this chapter.

2.1 History of IBM Informix 4GL

To fully understand IBM Informix 4GL is to fully understand the data and process
model of a business application in the generic sense, that is, the various program
states, the major entities used in the execution of a business application
deliverable, end-user program events, and so on. The operative phrase in that
statement is fully understand. Here we seek to define how business applications
operate so that we may optimize our activities as participants in the process of
designing and delivering business application systems.

2.1.1 Informix SQL (ISQL)

The precursor to 4GL is Informix SQL (ISQL). Many people assume that ISQL is
Informix version of, for example, Oracle SQL/Plus. The names Informix SQL, or
ISQL, may seem to imply that it is the Informix specific implementation of SQL,
for example, an ANSI standard SQL with Informix extensions. ISQL is a business
application development environment with data entry screen forms, printed
reports, navigation menus, and so on. ISQL would perhaps be better named
Informix Forms and Reports.

ISQL, like 4GL, offers character based programs. ISQL has a data entry forms
language (Perform), a printed reports language (Ace), user menus, and
interactive, ad hoc SQL statements.

The ISQL forms language, Perform, is largely declarative, meaning that data
alone comprises 70-90% of a Perform data entry screen form program. A small
amount of procedural program code is allowed after program events. In this
procedural section, one could perform check digit routines on entered values, do
validation via sub-selects, advance the field tabbing order in specific means, and
so on. The ISQL reports language, Ace, is also largely declarative. If you remove
the specific data formatting lines, Ace is also 70% or so non-procedural.

2.1.2 ISQL and IBM Informix 4GL

While ISQL is a very capable tool, 4GL is an even more capable tool. With ISQL,
one can deliver a data entry screen form that meets most of the business
requirements, but all ISQL forms look exactly the same; the menu is always on
line one, the menu commands names are hard coded, and the user interface to
page between long screen forms may be considered by some to be non-intuitive.
Conformant program deliverables can be a good thing when the style works for
you. 4GL allows one to create a fully customizable end-user program. The caveat
is, of course, you must do more programming.