Developing from scratch, you can lump the platforms into HTML and Proprietary.

NTL, Telewest and Ondigital use HTML. NTL and Telewest using a TV Specialist client-server middleware called Liberate (NTL have recently backed out of a contract with Liberate rival PowerTV). Ondigital uses a client side only browser and OS package from Netgem in France.

Despite all being compliant with HTML 3.2 and Javascript 1.1, and the two cable platforms being the same middleware, variations in implementation have meant that some aspects of Javascript includes, template sizing, graphic format other niggling details still have to be specific to each platform. There are ways to keep that minimal, but in our case they have arrived at only after a lot of accumulated experience.

Open is an utterly different animal. Its built in C++, as an application authoring environment, that speaks to an Application Server/Streaming environment. The API as a whole is from a company confusingly called OpenTV.

To develop in it, the developer must work in OpenAuthor and can use a limited range of functional objects, a limited number of template arrays, and a limited overall datasize for the entire application.

A number of suppliers have products to develop across the two types of platforms, and some private companies in the industry have built internal systems to tackle this.
Its hard to judge the market because most of these systems have been written with single clients or builds in mind.

Over time, however, its fairly clear that the push for standards (e.g. MHP, ATVEF) and cross platform CMS , are moving to Java, XML and IP as the underlying technologies

check out - nptv's bando, static's xminer

On 13:21:25 12 October 2000 matt wrote:
>With regards to the numerous available platforms for
>Interactive TV (Sky, NTL, Telewest, ONDigital), which
>platforms offer the reuse of code or presentation
>technologies. It would be preferable to obviously develop
>a presentation layer once for as many platforms at one
>time. Also, do any of these platforms tend to be more
>expensive and time consuming to develop for ? (I have
>heard that NTL supports an HTML like protocol)
>
>These issues are quite important in weighing up which
>platforms to target. Obviously, the current and
>forecasted usage statistics and demographics of each
>platform's users, TV network hosting costs will also
>contribute to this decision.
>
>Has anyone got any comments on the above, or ideas of
>where a central resource for this kind of information is
>available ?
>
>PS. What platform is HomeChoice (part of VideoNetworks)
>based upon.? I see that they have recently introduced an
>Interactive Shopping service.