1. Jim Fawcett CSE791 – Distributed Objects Spring 2001
COM and the Web
Jim Fawcett
CSE791 – Distributed Objects
Spring 2001

2. Web Programming Model Web Programming supports distributed processing:
Client-side:
XHTML, scripts, ActiveX controls, Java Applets
Server-side:
CGI (C,C++,Perl,…), ASP (Vbscript, JavaScript), ISAPI (C, C++)

3. Programming Models
Both browser and web-server support a programming model:
Browser – window/document/element
Web Server – Request & Response objects
In IE5 and IIS the programming model is derived from a parse tree:
IE5 builds parse tree from XHTML elements.
IIS builds parse tree from ASP pages and server-side scripts.

6. Powerful Programming Model
This is a very flexible, powerful model:
Can plug in reusable control components
Support methods, properties, events
Applications can support the browser and DHTML parser controls:
So both the application and the web page can determine what the user sees and how a user interacts with the system by interacting with the DHTML parse tree.

12. What does Control have to Provide?
To be hosted in a web page and communi-cate through events, the web page must:
Provide dispatch interfaces
Provide connectable objects for each event type
Implement IProvideClassInfo2
Implement IObjectSafety
Provide property persistance
Uses (parts of) structured storage
All of these are supported with Impl classes in ATL

13. What does Web Page have to Provide?
Object tag with control GUID
A script-based event handler
Script-based calls to control’s methods
Param tags to set properties
Very little work for Web Page designer.
A lot of work for the control designer.

14. DHTML Behaviors
The Browser model has been strengthened in IE5.5 by supporting behaviors:
A style-based subroutine that determines how a specific tag will behave.

23. Programming Model Again
This web programming model allows us to do some very interesting things:
We can build GUIs that the user can change easily, in some fundamental ways, if we base it on the web model, e.g.:
An application that provides basic resources.
Controls that provide reusable blocks of behavior
Controls can simply provide intricate behavior
They can also bind to data sources, e.g., xml or relational databases.
A web page that binds to controls, sets styles and behaviors, and provides most of the content.
The user can control the GUI by modifying DHTML