Programming in dBASE

Until now we have used the database for a very simple purpose, namely to extract information from a single file. However, it is also possible to connect several files. Let us suppose that we want to use dBASE for the following problem. In atomic absorption spectroscopy (AAS), one has to choose between the flame and the (flameless) graphite tube methods. The flame methods does not have such a low detection limit as the graphite tube, but it is easier to handle, less prone to interferences and more robust. For that reason the user s strategy will often be to apply the flame method above a certain concentration limit and the flameless method below it. The flame method has its own experimental characteristics and we suppose that we have another database file in which the characteristics for flame methods are given per element. In that case, we would like the consultation to go like this  

The following set of commands will permit to do this, however, without yielding the messages  

The first command use opens on disk drive A the database file flame which contains the characteristics for the flame method. Then the element Tl and the concentration (0.02 micro g/ml) one wants to analyze are stored in two memory variables melem and mconc , respectively. 

Before one can examine whether or not the detection limit is reached one has to move the record pointer to the record for thallium, which is done with the locate command. dBASE compares whether the concentration one wants to analyze is lower than the determination limit for the element (which is stored in concen , a field of the flame database file). dBASE then checks whether the equation (the last statement in the above set of commands) is. T. (True) or. F. (False). In case it is False, the concentration to be analyzed exceeds the determination limit and one can obtain the conditions for the flame method by typing the command display. However, if the concentration is lower than specified, the flameless method must be used. To obtain the conditions for the flameless method, one then has to open the database file containing the characteristics for the flameless method and use the display command. 

A very interesting feature of dBASE is that one can now write a program that carries out a number of commands automatically, and adds the messages. Such a procedure (called program or macro procedure) is given below  

---

In the same way that it is possible to program in dBASE, it is also possible to do this in LOTUS. Such programs are called Macros. Macros are based on the principle that all procedures in LOTUS Consists of a sequence of keystrokes. A macro is a collection of the keystrokes that make up the procedure one wants to automatize. 

---