Although this chapter is titled Page
Processing, information regarding the logic controls included
in the Page Processing alone is not enough, coverage of their
use during Page Rendering is also necessary. There are also
application level logic controls which execute when HTML DB
sessions are created during login.
Using Page Rendering and Page Processing
effectively can be somewhat confusing when learning to develop
applications using HTML DB. When I first saw the Page
Processing region, I was confused and did not know how to use
it. After all, I’ve been used to having to write every line of
code in other programming languages.
The fact is, Page Processing in HTML DB is a
clever method of providing logic control to developers of web
pages who do not have a programming background. The tricky part
is understanding what is happening, why it is happening, and
when it is happening. This chapter will help answer those
The Page Processing region is shown in
Figure 12.1. This example is taken from application page 29 of
the Sample Application included with HTML DB.
The Page Processing region contains the
logic that is to be executed when the page is submitted. The
items in the Page Processing region are called Logic Controls.
When the page is submitted, the HTML DB engine considers each of
the logic controls in a specific order determined by the
developer. The Conditions set on each of the logic controls is
the deciding factor on whether they will be executed. It is
just like a big IF … THEN statement for all the logic controls.
There is an exception to this rule. If one
of the processes or branches navigates off the page before the
logic control is considered by the HTML DB engine, it will be
ignored. This navigation is usually performed in a Before
Computation, Before Validation, or Before Processing branch.
Branches will be covered later in the chapter.