Each of the three mechanisms allows for elementary processing. The user can receive a Web page, type input into a form, and click a button to provide data for subsequent processing by application logic. Also, each mechanism allows a division of labor. A graphics designer who has minimal knowledge of software can create a Web page by dragging controls from a palette, dropping them on a drawing surface, and customizing them in a variety of ways.
Rich UI: In Rich UI, the application logic is EGL-generated JavaScript™ that runs in a browser. You write the code in EGL.
JavaServer Faces (JSF): Many Web applications are not based on client-side processing; they are server-centric. Logic on a server constructs a stream of HTML and transmits that stream to the browser. The user periodically submits data back to the server, which processes the input and responds with another HTML stream.
JSF is an important technology for developing server-centric Web applications.
Web transactions: As mentioned earlier, EGL also provides a third, less flexible way of serving business data to Web browsers. The developer in this case writes a program called a Web transaction, which is a pre-specified flow of logic that transmits Web pages and receives data back. A JEE-compliant application server is required. The primary purpose of Web transactions is to migrate code from IBM VisualAge Generator.
EGL-generated programs can process business logic and periodically display a text form: a set of character-based fields that are presented at a terminal or in a workstation window. After displaying the form, the program waits for user input. A particular keystroke (ENTER or a specified function key) causes the program to receive the user's input and continue processing.
This interface technology is called Text UI. It supports interactive COBOL applications that run on CICS, IBM i, or IMS. Text UI is also available for interactive Java applications; specifically, for JSE applications and JEE application clients. Use of this technology in Java is primarily to migrate code from IBM VisualAge Generator.
EGL includes a user-interface mechanism called Console UI, primarily for code migrated from Informix 4GL. In this case, the users interact with buttons, drop-down lists, and the like, in a workstation window. Console UI is available for JSE applications and JEE application clients.
The material in this topic is largely from Enterprise Web 2.0 with EGL (MC Press, 2009; http://www.mc-store.com/5107.html).