Why use EHLLAPI?
You can use the EHLLAPI functions to interface with legacy applications, to automate repetitive tasks, and to perform low-volume transactions. These functions are also useful for prototyping and implementing new applications quickly, without waiting for the software or hardware upgrades needed to support better communication protocols.
Your legacy applications do not need to be changed; they continue to operate as though a user is providing input to them. EHLLAPI allows you to build programs that use pieces of existing applications. For example, you can use EHLLAPI to capture an entire screen from the host. Your new programs can use the Communications/Transactions feature technology while maximizing the use of existing applications. Programs using EHLLAPI can also enable new functions to be delivered in stages. New programs can coexist with existing applications, and users of existing applications can migrate to the new programs at their discretion.
Using the EHLLAPI objects, you can isolate a program from the details of the origin of the data; the same application can continue to be used even if the source of the data changes. This is achieved through the polymorphic nature of object-oriented programming provided by Smalltalk: you can plug new objects into programs to replace existing objects, as long as they respond similarly.
Most complex EHLLAPI programs are very sensitive to changes in their environment. For this reason, traditional EHLLAPI programs tend to be hard to reuse. Their complexity is due to the number of parameters that must be adjusted to get them to work in a particular environment.
With the Communications/Transactions feature you can reuse EHLLAPI programs by subclassing them and overriding just the methods you need to make those programs work in a particular environment. Also, the polymorphic nature of Smalltalk allows you to plug new customized EHLLAPI programs immediately into existing client programs. This allows those client programs themselves to be reused without modification.
In addition, because Communications/Transactions EHLLAPI support can dynamically capture the format of the host screen, minor changes that do not affect the order of the fields will not affect your application.
Last modified date: 01/29/2015