Performance And most important, look for a product that performs

No one will publish that product performs poorly, so here are some clues that may indicate that product will not give you the that you

90% of base is on large mainframe computers.

Too much emphasis on user friendliness. If the 4GL is so end-user oriented that 'evcn an idiot can program there is usually too much overhead spent on supporting

The screens, reports are not compiled. ('Compilc' can differ- ent things to different vendors: is not as fast as object code.) No direct interface and write) to host operating system files.

The only way to evaluate the performance of a 4GL is to look at working applications that are similar to yours. Ask the vendor for a list of contacts at installed

in your and talk to those who use them.

16.3 DEVELOPING AN APPLICATION USING A 4GL-A CASE STUDY

The Phases in a 4GL

Let us see how the ABC system (developed in Appendix A using a would bc dcvclopcd using the Powerhouse product. The following sections can also provide a frarncwork for the phases in the development of a 4GL project.

Developing the Requirements Definition

The approach to analyzing the user's problems in a 4GL environment is much the same as in a 3GL environment. First a Document is written to define the user's problem. The RD for the 4GL is not as detailed as that of the 3GL one because thcuser's problems may hazy until afirstprototypeis built. Drawing a data- flow diagram is best way to begin, and the result would be the same as before Figure 6.1). As with a the next step is to detail each bubble. 16.4 details the Registrar bubble.

Chap. 16 Fourth Generation Languages

STUD. INFO

Figure 16.4 Data flow diagram of registrar functions using Excelerator

Define What-Analysis

There are three major differences between 3GL and 4GL analysis. First, with the 4GL the user must be familiar with the approach: he or she must realize that only a basic system of core functions will be built first, detailed functions and cosmetic changes will be added later, and after a limited number of iterations the final system will be ready.

The second difference is that the user will have to be a lot more active in a 4GL environment than in the spend a lot of time with the developers, perhaps even become familiar with the language. The user should also be aware that the system may not provideevery function exactly asrequested-thedeveloper may

functions (even changes in the business) so that the 4GL may be used most efficiently.

Third, the required for a to the language. In fact,

the analyst should be a developer as well.

In the 3GL SDLC the estimates at this stage were 50%-100% erroneous. With a 4GL the estimate should be only 20% in error. Why this improvement? Because you will have a much better handle on what needs to be done. The 4GL methodology is based on standard building blocks, plus limits can be put on the first prototype and the number of iterations. After the estimates are done, a formal proposal should be written to define project scope, cost and duration and to provide a milestone for this phase.

16.3 Developing an Application Using a 4GL-A Case Study

Define How-Design

T h e first i t e m t o d e f i n e in a 4GL d e v e l o p m e n t is t h e top l e v e l d e s i g n or b a s i c structure of t h e system. I t i s u s u a l l y easiest to use t h e b u s i n e s s f u n c t i o n s of t h e a p p l i c a t i o n as the b a s i s of t h e top l e v e l design. T h e in F i g u r e 16.5 follows t h e function b u b b l e s d e f i n e d in t h e d a t a flow d i a g r a m in F i g u r e and o t h e r s s u c h as F i g u r e 16.4.

REGISTER CANCEL STUD-DATA CHANGE UST HOW MANY?

PAYMENT REFUND HOW MUCH STUDENT TO HOW MUCH?

DO I OWE? INF. CHANGE WHO?

WHERE AM WHERE?

I ENROLLED? WHEN?

I

I I I

Figure 16.5 Top level design with business functions REGIS-

TRATION

SCHED. A CRS. INVENTORY REV.

CANC. A CRS. REORDER EXP.

MATERIAL MKTG.

TO COURSE FINANCE ADMIN-

ISTRATION

WARE- HOUSE

MANAGE- MENT

Chap. 16 Fourth Generation Languages

is undereachfunction box, shown in Figure

16.5 as the lower Read through the requirements document by itcm and ensure that all features are listed. Revise the TLD if necessary.

Design the File Structure

Files are designed at same time as structure of the system. Design the files way as before: First, the data entities and relationships, then define the fields in such a wav that all the accesses are as as and the fields are repeated as little (For more information on data base design

19 and 23.) However, there arc a more rules to followed when designing files

for a if an indexed structure such as RMS or IBM is

used.

1. Avoid variable length records.

2. Avoid variable content records.

3. Avoid records that are too long. is preferable to files with shorter records than fewer files with long records.

These rules arc more important with a 4GL than a 3GL because a 3GL such as COBOL variable length records with clauses such as the 'OCCURS n TIMES.' But most do not have an easy (default) way of processing records of variable length or content, forcing the developer to write procedures (which is no fun).

Look at the file defined earlier for ABC system (Section 7.8).

can redesign these files to variable length records as shown in Figure 16.6.

PK = Primary Key, SK=

16.3 Developing an Application Using a 4GL-A Case Study COURSE-MATERIAL

(One record course (One record per material) per material)