November 2007 Archives

Monsieur Dubray has posted nearly 5 blog entries critical about REST.

Almost everything Mr. Dubray claims "you're on your own" with REST is either a tremendous misunderstanding, an emotionally projected argument, confuses implementation technologies with protocol-based interoperability (e.g. SCA and SDO are jokes until it binds to the Microsoft stack, JJ), or it is in area where you're equally on your own with WS-*.

Contracts? WSDL is not a contract. XSD is not a contract. WS-Policy neither. They're interface descriptions. True contracts? You're on your own. By the way, REST relies on *very clear* contracts, as clear as anything in a well designed SOA. The difference is in how the architecture determines & applies them.

Versioning? XSD is notoriously flawed in this regard (though they're working on it). And there is more than that -- SLAs (no standard), security (WS-SecurityPolicy covers only some use cases), etc. You're on your own.

I had begun writing a point-by-point debunking, but, life's too short, and I'm busy enjoying Cancun at the moment. No one denies there's a lot of work to do in applying REST (or successor styles) to enterprise work, but that doesn't mean we shouldn't try. JJ, if you would like to have a reasonable conversation about this, let us know, otherwise please keep insulting us, any press is good press. ;-)

REST as a style in support of enterprise SOA is like XML, circa its release in 1997 -- great promise without a lot of satellite specs & infrastructure supporting it (in security, for example, though this is probably going to be fixed next).

WS-* is where CORBA was circa 1997: it will be used to implement some good systems, but there will also be some high profile failures. A number of the specs will likely never be adopted by the mainstream (see WS-CDL, WS-Eventing), though some will definitely improve some ridiculous vendor interoperability disputes (e.g. WS-TX, WS-RM). Plenty of pundits (now bloggers) sing of its imminent triumph (channelling Orfali, Harkey and Edwards), but overall, the framework will not help solve the problem that was used to sell its adoption in the first place: increased agility, reuse, and visibility in IT. I think many WS-* tools actively *hinder* an SOA architect from achieving these goals.

RESTful normalization

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Why is RESTful design thought to be hard? I said this during Sanjiva's talk at QCon, but here's my one line summary

RESTful design is like relational data normalization.

Even though both are driven by principles, both are an art, not a science. And the popular alternatives, unfortunately, tend to be driven by craft and expediency.

The analogy could be taken further: "good RESTful designs" today, of the WADL variety, are very similar to 1NF. With ROA and the "connectedness principle", we're just starting to move into 2NF territory, I think.

Witty aporisms abound: "The Key, the Whole Key, and Nothing but the Key, So Help me Codd" sounds a lot like "Cool URIs Don't Change".

We haven't quite yet found the RESTful 3rd Normal Form "Sweet Spot".

"Everyone knows that no one goes beyond 3NF", so perhaps RDF and the Semantic Web are REST's 6th Normal Form, because they "scare people". Amusingly, Chris Date actually seems to think so.

I just *really* hope we don't have to go through 20+ years of defending REST the way Codd & Date had to defend the relational model against unprincipled alternatives, a debate that continues to some degree almost 40 years after Codd's original paper. If, in 2037, we're still debating the merits of Roy's thesis, I'd rather be a bartender...

The REST track, hosted by Stefan, was great fun -- Floyd mentioned to me that the track in London wasn't so packed, but the room in San Fran was standing-room only for some of the talks. Stefan has rough notes of most of the proceedings on his site, so here are my reflections.

Steve Vinoski's talk was a good introduction to the crowd on REST's constraints and the desirable properties brought out of those constraints. "SOA Guy" brought out common counter-arguments from the SOA architect's position. A favorite point: SOA does not stand for "Special Object Annotations" :-) I also learned that we share a love of Mountain Dew (sadly decaffeinated in Canada, though).


One question from the crowd was: Isn't REST just pushing the interoperability protocol to the data type, not solving the interoperability problem? Here's my take: application protocols are about expectation management. Even though it's generic, the HTTP methods + metadata + response codes provide a wide range of signs, signals, and expectations for communication. So, while it's not aligned to what you're doing specifically, it means that we can discover & communicate, generically, almost any piece of information -- a very valuable form of interoperability.


This does not, of course, solve the the data (MIME) type tower of babel. That's the next battle. There is a tradeoff between intertwingling syntax and semantics. Doing so, like with XML Schema and its ilk, is easier for programmers, but harder to interoperate if the domain is business-biased. There's more potential for disagreement when designing a data format for an industry than for some general-purpose infrastructure. On the other hand, using a generic syntax, whether Microformat-based XHTML, is a bit harder to program with, requiring tools support, but arguably could lead to better interoperability. And, taking this progression further, a completely generic logical data format, like RDF/XML, is even harder to program for, but once the tools exist (similar to SQL query engines), the potential is vast.


A more few reflections. Why do people misunderstand REST? For example, REST and WOA are about anarchy & avoiding standardization according to this gentleman. Who are these WOA people he speaks of? This strikes me as a projected argument, something that's derived from the emotional reaction of "I'm afraid you are saying X", when the Other isn't actually saying X. It reminds me of the early days of Extreme Programming, where pundits claimed "Egads, XPers say you should not design your software!"

Another example, is "You REST people think it will take everything over and be the only architecture!" Which is again, an emotionally projected argument, something I don't think anyone is actually saying. The points are that effective architecture at scale requires emergent properties to be induced through constraints, and that networked hypermedia might be a shift in thinking in the way that objects were a shift, and deserves attention. (Apparently we're in the mid-70's Smalltalk phase of that revolution, however. :-)

There are two common angles where I think people miss the point of REST here:

  1. When people don't believe there's such a thing as emergence;
  2. When people don't get/remember or relate solid software engineering principles to their distributed systems. In particular: interface segregation, and stable dependencies and abstractions. REST is really just a pattern that takes those principles seriously for a collaborative information system.

On to the further talks....


Sanvija's talk brought out the most useful debate of the day -- there's so much more dialogue that could (and SHOULD) happen on every one of those slides, to absorb where we misunderstand each other. Stefan's blog entry captures a lot of my questions and comments that I made during this session; afterwards I thanked Sanjiva for putting up with me. ;-) Hopefully this one will be posted in InfoQ.com sooner rather than later, it was a fun time.


Pete Lacey went through demonstrating the 'ilities' of REST, where he discussed the constraints and properties in more detail and, in code showed an XHTML-based (but also Atom and plain XML representation-based) REST API for an expense reporting system. He proceeded to show integration via a Microformat browser, curl, ruby, Microsoft Excel, and Word.

This sort of demo is very important, as it's the only way I think people will begin to get what serendipitous reuse is about. Not everything is encoded in a managed business process -- Microsoft Office still glues a vast amount of business activity together!


Dan Diephouse discussed building services with the Atom Publishing Protocol. I enjoyed this: it was hands on, code-oriented, and wasn't just a love-in: we spoke equally of the benefits and current open challenges with this approach to publishing data on the web.


And, though I met him at lunch, I unfortunately missed Jim Webber's final talk of the track day, due to some work commitments! Hopefully I'll catch the video when it's posted on InfoQ.

Kent Beck gave the first keynote speech at QCon, which was a good talk on the trend towards honest relationships, transparency, and sustainable commitments in software development: the "agile way" is aligned with the broader business trends like Sarbanes-Oxley, greater transparency, board and management accountability, etc.. He claimed during the keynote (I'm paraphrasing):


"Agility is an attitude regarding one's response to change."


I asked him the following two part question:


"There seem to be two trends in industry -- the Agile methods movement, which is about Agility as an attitude, and the Agile architectures movement, which is about introducing enterprise-level and "systems of systems" level architectures that help to enable greater agility. The questions are:


1. Do you believe architecture actually can enable greater agility? Regardless of what religious school you belong to, SOA, REST, Data Warehousing, etc.


2. How do Agile teams, with the attitude, build productive relationships with Enterprise Architecture teams, whose goals and attitudes often are at odds with the executing team?"


Kent's Answer for #1 (paraphrasing): "I've always believed that design matters, from the smallest implementation detail, to the largest architectural arrangement of software. Design can enhance communication."


Kent's Answer for #2 (paraphrasing again): "It can be a hard thing, but it's important to recognize that the EA saying 'you can't code without our approval', and the developer having to wait three months, doesn't have to be about a power struggle. There are two different principles and values at play here, both attempting to get to agility. The goal must be to get past the noise of the specifics like 'you need to build things this way' and find a shared understanding of the principles that underlie such decisions. If I, as an Agile team leader, believe in principles like the time value of money, or in the lean principle of flow, I'm going to try my best to ensure that there is a shared understanding of their impacts. Similarly I would hope to understand the principles that underly the EA's decisions and policies. It's the only way to get past the politics."


Richard Gabriel, always thought provoking, gave two talks that I attended. The first was:


"Architectures of extraordinarily large, self-sustaining systems"


So, assuming a system that was trillions of lines of code, millions of elements, thousands of stakeholders, beyond human comprehension, and must provide advantages over an adversary, how would you design such a system?

Firstly, a reflection on the requirements. The "gaining advantages over an adversary" part of this description seems to be similar to the Net Centric Warfare (NCW) movement -- it's very Strategy as Competition oriented, I'm not sure I agree it's the right frame of mind for thinking of this sort of thing, but it probably belies who is funding the effort. Lately I have noticed that NCW is becoming more and more "Web-like" and less "SOA-like". The publication, Power to the Edge, a revised treatise on NCW concepts, really screams out "Web!", or at least some successor to it. Strassmann more or less predicted this in the early 90's while he was running the DoD, and correctly surmised that it's political and human comprehension that's holding up the transition.

Back to the talk. Dick Gabriel explored three approaches to design:

  1. inverse modeling is tractable -- meaning, we can work out the design of the system top-down, and in advance
  2. inverse modeling is intractable -- meaning, stepwise refinement (ala. 'agile design')
  3. evolutionary design -- wherein we use evolutionary techniques, such as genetic algorithms, to "grow" a solution. The design is indistinguishable from the implementation this case.

On #3, he pointed to Adrian Thompson's work on Evolutionary Electronics. This was some of the creepiest, coolest, and most bizarre results one could imagine: Adrian literally "grew" a 10x10 section of an FPGA, using genetic algorithms, to solve a simple tone discrimination task. It executes the task flawlessly. The problem is, they don't actually know how it all works! See the paper here.

Reflection: I was surprised he did not speak about the work on "collaborative systems" or "systems of systems" by Mark Maier (of IEEE 1471-2000 fame) and Eberhardt Rechtin. This approach fits in with Roy Fielding's REST dissertation on the beginnings of an architecture science: inducing emergent properties on a system by way of constraints. I was going to speak with him about it, but he was mobbed by several attendees at the end, and figured I'd get my chance some other day....

Dick noted that "the Internet" as a whole isn't really an "ultra large scale system" that he's looking at because it doesn't have a directed purpose. This is curious -- the Web, an application of the internet, had a goal: increase the sharing information of any type, globally, exploiting Reed's law.

The Web doesn't have an adversary though... does it? Hmmm, maybe it does.

Dick's second talk was a repeat of his OOPSLA presentation 50 in 50, a whirlwind tour of many programming languages over the past 50 years, accompanied by music. This presentation is available via OOPSLA podcast, and while it doesn't quite work without the visuals, I recommend it if you're interested in how much creativity there has been out there (and how, we're only starting to regain some of that creativity now after 10+ years of JavaJavaJava). Hopefully the slides will be eventually made available as a Quicktime...


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