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4.1.2 Initialization

The PAO is totally configurable, which means that every time a PAO is instantiated by the application server, its attributes (name, service, server, port and PICI) are provided by a special PROGRESS property file. The parametric instantiation of a PAO is similar to the initialization process of general application objects as described in Section 2.2.1. The initialization of a PAO is divided into two steps. The first step is setting the basic attributes (name, service, server and port) which are simple objects (strings and integers) that can be coded directly within the property file. The second step is the instantiation of PICI which is a bit more complicated. Therefore, we code an example input value for the denoted service as a PROGRESS language string in the property file. On the one hand, this string provides the structure of the request arguments (which corresponds to the structure of the PICI) and on the other hand it is a valid input useful in a first execution. Because we do not want to implement a PROGRESS language parser within a PAO, we use a special service (str2pg) that each PROGRESS server supports. This service simply transforms a string given in the PROGRESS language into a corresponding PROGRESS object. The above mentioned Java package of PROGRESS then allows us to construct the actual PICI for this PAO.

Now that the PAO has been constructed, it offers the underlying PROGRESS service transparently to the application server (respectively the clients) through a general interface (the PICI). Figure 3 schematically shows the structure of the PROGRESS property file.

  
figure47

Figure 3: Scheme of the Progress property file


next up previous
Next: 4.1.3 Handling of PAOs Up: The Integration of the Previous: The PROGRESS Application Object

Ralf-Dieter Schimkat
Thu Dec 9 14:08:00 GMT+1 1999