COMMON AREA or PARAMETER LIST

Although both forms of parameter passing are supported by PARADYME , it is suggested that user should use the PARAMETER LIST approach over the COMMON AREA method. This is because a large number of support programs have been written based on the standard COMMON area. If the COMMON area is changed, the probability is that many of these support programs cannot be used. These will then have to be re-written by the user, thereby increasing the development time.

On many systems, the COMMON AREA is placed at the start of the symbol table, which means that these items will be the first ones accessed, whereas the PARAMETER LIST variables are at the end and so take longer to access. This in turn can lead to a degradation in system performance. Against this is the increased flexibility in using PARAMETER LISTS, in that only the calling programs and the called program need to be changed if the PARAMETER LIST is changed. If a change is made to the COMMON area, the probability is that most of the programs in the system will require recompilation. This is due the global nature of a COMMON area declaration as compared to the more localised impact of PARAMETER LISTS.

One feature that is available on some systems are LABELLED COMMON AREAS. These have been available on some systems for many years. Let's hope that it's not to long before they are widely available on PICK systems as this would resolve many of the problems facing systems developers.

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