If anyone has developed an end to end iTV solution they would know the difficultities developing user interfaces that run on OnDigital, Telewest, NTL and Open.

The standard approach has been to create four separate sites using HTML or Open Authoring Tool. The limitations of the set top boxes in regards to cookie sessions and no client-side form validation need to be overcome by taking all client-side processing server-side. By using XML and XSLT developers are now able to do styling and formatting server-side as well.

If we use a Microsoft solution as an example. A typical iTV solution would consist of ASP (Active Server Pages), COM objects and SQL Server.

ASP will make object calls to through a COM layer to SQL Server then render HTML 3.2 with Javascript 1.1 to say a liberate iTV set top box through the provider's server.

This works fine if you are using only one provider. However two or more providers you need to have separate ASP layers for each.

By replacing SQL recordsets with XML recordsets you can use XSLT (Extensible Stylesheet Language Transformations) like a server side style sheet. An ASP page will detect the platform (i.e. NTL or OnDigital) then call the appropriate XLST template.

This template will contain the screen, language and page formatting of the appropriate iTV provider. It can even call different HTML schemas to insure the correct tags are used. For example Telewest use HTML 3.2 so you cannot use <DIV> tags.

ASP is still used as a rendering template but all platform interface design is handled by XSLT.

By creating a server side stylesheet layer the development team can centralise all the logic and data layers for multiple iTV platforms, as well as the Internet and mobile (if you are really brave!!!).

In regards to the Open platform, the company has announced a move to WML as a replacment for the Open Authoring Tool. This means that XML / XSLT could be used to define the WML DTD (Document Type Definition) for the Open platform.

The result could mean a new standard for the development of iTV sites. XML / XSLT will act like a server side presentation layer separating the business logic from the user interafcae.

If you have any thoughts on this topic, I would love to hear them.