WebsydianExpress Application Architecture

• Overview
• Web Application Flow
• Events and Web Input
• Response Page and HTML Templates
  • HTML template layout
  • Create HTML page
  • Generate Events and Web Input

Overview

This document describes the application architecture for web applications developed with WebsydianExpress.

It also gives an overview of the steps needed when developing a web application. For more detailed information on how to develop web applications with WebsydianExpress please refer to the example business processes.

Web Application Flow

The figure below shows the flow when a web application processes a request from the browser.

Figure 1: Web application flow

1. A user presses a button or a link in the browser.
2. A request is sent from the browser to the web application. If the user has entered any values these are sent with the request.
3. The web application receives the request and processes the values sent in the request.
4. The web application generates a response to the browser. The response will typically be an HTML page.
5. The HTML page is sent back to the browser which will display the HTML page for the user, and the flow continues from step 1.

This flow is very similar to what happens in a 5250 application where the application also responds to user interactions with a new "page" (5250 panel). However, there are some substantial differences which have impact on how web applications should be developed. For more information please read 5250 Application Development vs. Web Application Development

In the figure above it is step 3 and 4 that are relevant for the web application developer. The rest of this document describes how to handle these steps and what to do in each case.

Events and Web Input

An event represents an action performed by the user. This could be a press on a button or a click on a hyperlink in the browser page. When an event is activated the browser will send a request to the web application specifying the ID of the event that was activated.

In some cases it is relevant for the user to specify input data before the event is activated. In these situations the input data is sent with the request along with the event ID, and the web application processing the event will then have access to these input data. In the rest of this document and in the documentation this input data is referred to as "web input".

To process an event the web application must do the following:

1. Use GetEventID to retrieve the event ID of the request.
2. Use GetParm and ValidateParm to fetch and validate secure parameters.
3. Use GetInput to access web input values.
4. Perform application specific processing of the web input data.

Please read the section Generate Events and Web Input for more information about events and event IDs.

Response Page and HTML Templates

Once the event and any eventual web input values have been processed, the web application must generate an HTML page and return this to the browser. In WebsydianExpress HTML pages are generated using HTML templates.

An HTML template is an HTML page that contains special markers specifying where output values should be inserted. These special markers are called replacement markers.

So in order to generate the HTML page the web application must use an HTML template and then specify the values that should be inserted instead of the replacement markers.

This approach separates the layout from the functionality of the web application. The layout is determined by the HTML template, and can be modified by a web layouter without any changes to the application.

HTML template layout

To construct an HTML template the Page Modeler is used. In the Page Modeler a page is defined for each HTML template needed by the web application. So each page corresponds to an HTML template. To find more information about the Page Modeler please refer to the documentation for the Page Modeler.

With the Page Modeler it is possible to define the basic structure of the HTML page in terms of the events and output fields that should be on the page.

The following page elements can be added to a page:

Field

Represents a field on the page. Fields can be added to the page, grid region, or to an event. A field on an event represents an input field whereas a field on the page or the grid represents an output field.

Event

Represents an event on the page. Events can be added to the page or to the grid.

Grid

Used to construct tables.

Once the structure of the page is defined then the Page Modeler can be used to create the HTML template. The created HTML template is then used by the web application to generate HTML pages at runtime. The HTML template can be used as is, but it can also be further layouted, e.g. using FrontPage, if that is necessary. Please read HTML Templates and Replacement Markers for more information.

The web application refers to the HTML template using a template ID. The template ID is the file name of the HTML template (excluding the .HTM suffix).

Create HTML page

Once an HTML template has been created it can be used by the web application to create HTML pages as response to user events.

In order to create an HTML page and send it to the browser the following must be done:

1. Setup the data to be outputted to the page using the API functions SetOutput and SetGridOutput. These functions need the ID of the HTML template and the name of the replacement marker to substitute with the data.
2. Generate and send the HTML page to the browser using the API function WritePage.

Generate Events and Web Input

In order for a user to activate an event, information about the event must be generated on the HTML page. An event (including the event ID) is defined in the Page Modeler and the event will be stored in the HTML template when created by the Page Modeler.

So events are generated automatically on the HTML page based on the definitions in the HTML template.

There are two cases where the web application must do some further action when setting up information for an event: When setting initial values for an input field or when using secure parameters.

Initial values

To set an initial value for an input field in an event use SetOutput if the event is in the page or SetGridOutput if the event is in the grid. This will then set the initial value for the input field and it is this value that will be sent if the user does not specify any input in the field when the event is activated.

Secure parameters

In some cases it is necessary to store some hidden information with an event. E.g. when presenting the user of a list of invoices to select, then the database key of each invoice record must be stored as hidden information in the select event. The key will then be sent as part of the request when the user activates the select event, and the web application will then know which invoice has been selected.

This hidden information is called secure parameters because values are transferred from the program generating the HTML page to the program handling the event generated on the HTML page, and they are secured by a signature so the web application detects if the parameters are modified.

To create secure parameters for an event use SetParm for an event on the page and SetGridParm for an event in a grid.