Hi all, Thanks for a thought-provoking week of emails on the OCCI-WG list. Especially thanks to Sam, Richard, Ben and Tim for laying out a lot of the issues. One link that I found useful was this: http://www.tbray.org/ongoing/When/200x/2009/03/16/Sun-Cloud where we find the following statement: --- if Cloud technology is going to take off, there’ll have to be a competitive ecosystem; so that when you bet on a service provider, if the relationship doesn’t work out there’s a way to take your business to another provider with relatively little operational pain. Put another way: no lock-in. ... I got all excited about this back in January at that Cloud Interop session. Anant Jhingran, an IBM VIP, spoke up and said “Customers don’t want interoperability, they want integration.” ... “Bzzzzzzzzzt! Wrong!” I thought. But then I realized he was only half wrong; anyone going down this road needs integration and interoperability. --- What we have been discussing is "for customers". So it is about both of these things: * Interoperability ("interop") * Integration This made me realise that our OCCI discussions have correctly been about both issues. But, incorrectly, we have been commingling the two. For example a person will say "you need X for interop" and the reply will be "but you need Y" when in fact Y is for integration. And vice versa. This is a problem for us because it leads to confusion. But it's a symptom of a larger problem which is that interop and integration have opposite requirements. * Interop is about reducing the entropy in a general purpose system down to some level of behavioural invariance. This minimises the cost of meeting the defined behaviour correctly, and minimises the risk of different behaviours breaking interop. This is in turn about having a defined behaviour (in some format) and minimising its scope. * Integration is about minimising the frictions between (a) the general purpose system and (b) any specific purpose external system that may be coupled to it. It is also, often, about maximising the number of specific systems (or "features") that may be connected. Since we don't know ex ante what those are, this tends to maximise scope (eg "feature creep"). Too much specificity is the same as complexity. Because interop requires minimal scope, and integration pushes for maximal scope, they are in tension. They are BOTH about simplicity. Simplicity cannot be invoked on its own, as a reason for preferring interop over integration: * Interop is about simplicity of definition * Integration is about simplicity of end use BUT * Interop simplicity is ex ante * Integration simplicity is ex post We cannot predict all ex post issues, but we can try and make simple definitions ex ante. I argue below this means we have to have ONE definition. So let's look at interop first: It's really important that interop be based on defined behaviour. Or it cannot be verified. Lack of verifiability is almost always a symptom that something is opaque, complex and ambiguous, which will break interop in subtle ways that cannot be seen in advance (due to the opacity). This later leads to brittleness when interop and integration are attempted in practice; and that leads to expensive patching at all levels, ... which is one thing that WS-* exhibits. NOTE 1 on WS-* ---- IMO this was not accidental, and due to focussing on solving integration before solving interop. IIRC, the first WS-* was an Interop committee to fix minor vendor mismatches and versioning issues in prior WS protocols such as WSDL and SOAP. The formalisms of WSDL and SOAP were not precise enough to spot these issues upfront, so they were left until it was too late. Now let's look at the implications of having a definition of behaviour: You cannot define a system using multiple definitions. You have to have one definition, preferably in a formalism that admits of automatic conformance testing. In the case of data formats, this leads us to three possible choices: 1) We remove data formats from the interop profile. They are not part of interop. Data interop is excluded. Data payloads are opaque blobs. OR 2) We have one data format that can be defined unambiguously. OR 3) We have multiple formats and derive them from a single unambiguous definition using canonical, verifiable, automatable, mappings. This definition can either be in a new format which we invent (option 3a) or it can be in an existing format (option 3b). I am going to rule out option (3a) on grounds of time and due to the prevalence of existing candidates. Also, I think choice (1) is a complete cop-out -- I don't see how we can claim 'useful' interop without data interop. This leaves options (2) and (3b). BOTH of these options require one format. By occam's razor, option 2 is preferable on grounds of simplicity - option (3b) does not add anything except one mapping for every extra format that is based on the core definition. Such complexity MUST be deferred as long as possible, and MAY be pushed into integration use cases. The latter is preferable. Complexity MAY be added later if necessary and then, reluctantly. As a general observation if you have complexity (entropy) in a system, it is very hard to take out. It may permeate the system at all levels. Removal of the complexity is known as 'complete refactoring'. This is a bad outcome. Even worse is when refactoring cannot be done for commercial reasons, eg because the systems are in production. Then the complexity must be encapsulated and hidden. Attempts to wrap complex behaviours in simpler packaging usually fail. NOTE 2 on WS-* ---- This tried to do too much and ended up trying to wrap the complexity in simple packaging. This usually fails to work as we have seen. Another general observation: * Integration requires interop, ie. the use of a common general interop model; otherwise it is piecemeal and pointless. Example - the old 'integration brokers' that had N*N connections to maintain, and which got replaced by N connections to a common system. * But you can have interop without integration - it just means 'you have a smaller audience'. This is fine because you can always grow your audience by integrating more case with the interoperating core. It is easier to do that when the interoperating core is programmatically simple (as in low entropy, small code blocks, easy to test conformance to the definition). I would like to add some observations from the world of AMQP... AMQP-1) It is a protocol with one simple common data format - it gets that right. We leave it to integration products and services to support data formats at the edge (eg "ESBs"). OCCI should not be like an ESB - that is for products and services in the integration business. AMQP-2) That AMQP data format is not XML - see below for more thoughts on that. XML can be carried as an attached payload (just as it can be in the JSON case btw). AMQP-3) The 0-8 and 0-9 specs took 18 months of production use to show up the many very tiny interop bugs. We used those to create 0-9-1 which does have interop (we have tested this) and is only 40 pages long. This would not have been possible with a complex spec. It would not have been possible with multiple data formats. AMQP-4) The 0-10 spec was focussed on supporting a lot of use cases eg "integrate with multiple transport formats including SCTP and TCP and UDP" and adding lots of features at all levels (eg JMS, support for hardware, ..). That spec is really complicated and nearly 300 pages long. Some great new ideas are in it, but it's long and in my own opinion not supportive of two interoperating implementations. AMQP-5) All these painful lessons have taken the AMQP working group to a much happier place with AMQP 1.0 which tries to simplify everything by taking stuff out that is not needed for interop, plus refactoring (see above my comments on how removing entropy is hard) and clean-up. All of the above has taken time because we did not learn from WS-*. We did too much too fast and confused interop with integration. We are back on track now. Now to the issue of data formats. I have already argued that FOR INTEROP, there must be one definition. I argued that the best way to do this is via a suitable single format. We can support as many recommended ways as we like FOR INTEGRATION ... and they can be evolved over time. Here is my 2c on XML. XML-1) XML lets you do too much - because of namespaces and xsd it is in effect multiple formats. This is bad - we want a single, testable, constrained definition for data interop. XML-2) To enforce compliance with a simple XML definition, you need to have an extra definition of a well formed 'small' document. But creating a new definition of a data format in XML is equivalent to defining a new data format, the same as 'option 3a' above. But that option was ruled out above, on grounds of time constraint.. provided that a suitable alternative exists already (see JSON claims below). NOTE 3 on WS-* ---- IMHO a third reason why WS-* failed to be simple enough to get happy, quick and wide adoption, is that (XML-1) issue left too much data integration in the hands of customers, because vendors could not produce useful products when XML could be all things to all people. By not delivering on data integration, it became hard to deliver on the promise of integration at all. And recall that lowering integration costs was the selling point... So let's get INTEROP right and then do INTEGRATION. Interop requires: * Model - yes * Data format - one definition * Metadata - ? tbd As an aside - I think that GData is the nuts but it is also really an *integration techonology*. Now, here are some claims about JSON: JSON-1) Sun have demonstrated that it is plausible as a data model for a cloud API. That makes it plausible for us to ask: can it be used as the core definition for interop? JSON-2) It is lower entropy than XML. This makes it easy to test conformance. JSON-3) This means we do things the right way round -- simpler 'ex ante' choices make it EASIER for us to extend and enhance the protocol on a by need basis. For example carrying OVF payloads, or other integration points. Many will be done by users. So my recommendation is that the best way to avoid WS-* outcomes is A) Use one format for interop. Do interop first. Integration later. B) *At least for now* and *during the working draft* stage, to use JSON C) Other formats, for now, are "integration". But we do interop first. OK.... I have to run off. I wrote this down in one go and don't have time to review it. Apologies for any mistakes in the presentation. What do you all think? alexis