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Hi,
I’ve been lurking on this list for several months. I have no idea what the protocol is for introducing myself and whether or not I’m allowed to speak up – as my company is not a member of the OPES group. However, until recently I worked at Sprint, where my team issued an RFP for an “Intermediation” system earlier this year i.e. a customer requirement for an open pluggable edge server. I know a lot about this topic as my team at Sprint built a working prototype of such a system and implemented micropayments and other intermediation functions. We demoed this at the Sprint Developers Conference in Las Vegas, during October 2001.
I have watched this debate about callout chaining for some time. I would like to make several observations and identify what I believe to be several underlying and unspoken assumptions in the group.
It seems to be assumed that the market does not know what it wants or whether it needs this technology. It is being designed by technologists. However, there does exist a marketing requirements document from a large telco. Sprint published one.
The argument around chaining can be abstracted down to whether or not callouts can be loosely coupled and functionally cohesive, or whether procedural coupling is required. This is the 30 year old debate in software engineering about procedural versus functional decomposition.
There appears to be an underlying assumption that the switching cost of invoking a callout is high. If this were so, then procedural coupling would produce a performance enhancement by reducing the number of redundant switching calculations. However, if the switching cost of invoking a callout is low, in comparison to the processing time of the individual callout functions, then there is little performance improvement to be achieved from procedural coupling i.e. chaining.
To decide whether chaining is worth the cost of the protocol overhead and the need for the callout server, to act as an OPES server (in order to chain), the group must decide whether the switching cost of invoking an OPES callout from the flow of the network, is significant. It would appear that determining whether or not this is significant cannot be achieved until a first cut of the specification is agreed and the performance can be determined.
Hence, it would seem too early to make a call on whether or not chaining is worthwhile.
Is chaining even needed? To understand this, we must evaluate whether or not procedural designs will emerge. We must look to the uses and the usage of an OPES system and decide whether chaining seems likely.
For example, let’s imagine the mainline network is http. We are interested in switching http requests or responses for two reasons: micropayments – pay per click, subscribe to a set or URLs e.g. New York Times Today; automatic form fill – a la MS Passport without the application layer interface, i.e. no need to re-write the URL with a defined set of name value pairs for identity. Those are just two examples. At the last count my team had 11 applications for an OPES style system.
Now consider whether it is likely that we would switch on the same URL for two different applications, i.e. is it likely that the same URL which needs a micropayment challenge, would also require a form fill?
The underlying assumption on this list is that it is too early to second guess the market and the possible usage of OPES. Hence, the specification should be as flexible as possible. However, flexibility comes at a cost. It adds complexity, risk and time to market.
IMO, providing an OPES 1.0 spec which allows functional callout is a major step forward. It might be better to take the option theory approach and decide to keep your options open regarding chaining. There is no guarantee that the market needs chaining. If later there is demand then exercise your option and build it into a subsequent version of the specification.
Regards,
David
...... ::4thpass e-mail dja@xxxxxxxxxxx
-----Original Message-----
good points so far, I also think that chaining will also add difficulties
on tracing. On the otherhand, I could also see the benefits of chaining if it is done right. However, My personal opinion at this stage of the game is to start simple with an eye on expansion, so basically let us start with no chaining and keep this option open for later. abbie
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