dBASE IV OVER dBASE III PLUS
Kazi Sayeda Momtaz (Sharmin)
dBASE IV is the latest addition of the dBASE series. dBASE IV is designed with a totally different architecture from its predecessors. Many new functions, commands, and options have been added to almost all previous features, such as reports, labels, screen forms, application generation, etc. Actually, dBASE IV is more powerful and user friendly.
The Control Centre replaces the dBASE III+Assistant mode which is the entry point in dBASE IV. Control Centre provides access to most of the DOS command i.e., without leaving dBASE IV.
We know that the maximum 128 fields can be used in dBASE III+ but in dBASE IV a database file can have up to 255 fields and up to 99 fields of all types including 10 database files can have up to 47 index files.
Another advantage is automatic program compilation. If we want to compile the dBASE III+ programs we have to use some other software such as clipper. dBASE IV includes a built-in compiler which automatically compiles our programs to speed up programs execution. All object codes created when we design our reports, customs screens, labels etc. are converted into the dBASE IV source code. So that we can combine all these into a ‘single program’ if we want to market our programs as a package. For this reason programmers like dBASE IV over dBASE III+.
Instead of several separate index files for a database file, dBASE IV maintains a single production index file which has the same name as the database file but which- a file extension ‘mdx’. All index files are stored in the production index file, and any time when we want to open a database file, the corresponding production index file is automatically opened and we can add, delete, change data in any record of the file without hesitating about the index files. So it is a great advantage to us.
In dBASE IV report now includes a “header” and a “Footer”. It permits an unlimited number of subtotal-ling operations whereas in dBASE III+ there were only two but in dBASE IV unlimited. So nice. The report design screen permits use of special print features, such as bold, underline, different pitch i.e., compressed printing etc. So from dBASE report file we can design our text like wordProcessor. So it is another advantage for the programmer. Similarly the label design permit us to design any kind of label what we want. The important new features that have been added include a facility to use the graphics characters in the screen; several new picture functions such as centering or right aligning data in field removing leading and trailing blank spaces and multiple choice display and selection; massages to be displayed while entering data in fields; carry forward or default values for selected fields; coloring of selected area of forms etc.
In dBASE IV a new loop Scan-Endscan has been introduced, which can be an efficient alternative to Do while.not.eofQ—Enddo loop in several cases. For example,
Clear
Use marks
Do while .not. eof()
If name = ‘Nasima’
List roll, name, marks
Endif
Skip
Enddo
We can use the Scan-Endscan loop
Clear
Use marks
Scan for name = ‘Nasima’
List roll, name, marks
Endscan
Query By Example (QBE) is an easy method of retrieving the required information from a database file. It is a significant improvement over dBASE III+. In dBASE IV we can install up to four printers. One of them is the default printer and the others may be selected as and when required. In dBASE IV we can select a default data format such as American, ANSI, British, French, German, Italian, Japanese, USA and others. Similarly we can also define the currency symbol as Cent, Pound, Yen, Peseta or Franc. We can also change the clock format. Again in
case of date we don’t have to write a date as a character. If we simply enclose a date type data in braces like {10/10/931 to tell that it is a date and then Dion automatically converts a date-type field into a character string in the format “1993/10/10″. This function is also useful for indexing a database file on a date field.
In dBASE IV, we can define our required function. Once defined, these functions can be used anywhere in a program. User defined functions are similar to a procedure and are stored in the procedure file and begin with Function <function name> and end with Return command. Again in dBASE IV, it can hold up to 1,092 procedures and user defined functions whereas in dBASE III+ we can use only 32 procedure file. So it is a more advantage.
dBASE IV has added Windows. A window is basically a Pop-up screen which is temporarily shown superimposed on an existing screen display. Later, when dBASE IV wants to remove it, the original screen is restored within no time. Windows are also used for displaying memo fields.
In dBASE IV Rollback is another command permits a database file to be restored in a previous stage. This is actually useful in case of power failure. Again keyboard macro is a new facility which can be used to enter a lengthy sequence of depressions of keystrokes required for certain dBASE IV operations just by pressing a single key. In dBASE IV array is used. An array is nothing but subscripted memory variables.
New four financial functions have been introduced in dBASE IV. They are: FVO, PVO, PAYMENTO, NPVfJ. Again for improving searching another newfunctions have been added like SoundexfJ. SoundexfJ function permits searching for words which may have different spellings but sound alike.
There are several other new commands and functions. These commands and functions makes dBASE IV and extremely powerful language. But if we really want to know dBASE IV we have to actually use dBASE IV to really know how powerful it is.
Reference :
dBASE III PLUS MADE SIMPLE
WITH dBASE IV and FoxBASE+
Authors bio is coming up shortly. 
