Category Archives: Mashup

Redeeming the service description document

A bicycle is a convenient way to go buy cigarettes. Until one day you realize that buying cigarettes is a bad idea. At which point you throw away your bicycle.

Sounds illogical? Well, that’s pretty much what the industry has done with service descriptions. It went this way: people used WSDL (and stub generation tools built around it) to build distributed applications that shared too much. Some people eventually realized that was a bad approach. So they threw out the whole idea of a service description. And now, in the age of APIs, we are no more advanced than we were 15 years ago in terms of documenting application contracts. It’s tragic.

The main fallacies involved in this stagnation are:

  • Assuming that service descriptions are meant to auto-generate all-encompassing program stubs,
  • Looking for the One True Description for a given service,
  • Automatically validating messages based on the service description.

I’ll leave the first one aside, it’s been widely covered. Let’s drill in a bit into the other two.

There is NOT One True Description for a given service

Many years ago, in the same galaxy where we live today (only a few miles from here, actually), was a development team which had to implement a web service for a specific WSDL. They fed the WSDL to their SOAP stack. This was back in the days when WSDL interoperability was a “promise” in the “political campaign” sense of the term so of course it didn’t work. As a result, they gave up on their SOAP stack and implemented the service as a servlet. Which, for a team new to XML, meant a long delay and countless bugs. I’ll always remember the look on the dev lead’s face when I showed him how 2 minutes and a text editor were all you needed to turn the offending WSDL in to a completely equivalent WSDL (from the point of view of on-the-wire messages) that their toolkit would accept.

(I forgot what the exact issue was, maybe having operations with different exchange patterns within the same PortType; or maybe it used an XSD construct not supported by the toolkit, and it was just a matter of removing this constraint and moving it from schema to code. In any case something that could easily be changed by editing the WSDL and the consumer of the service wouldn’t need to know anything about it.)

A service description is not the literal word of God. That’s true no matter where you get it from (unless it’s hand-delivered by an angel, I guess). Just because adding “?wsdl” to the URL of a Web service returns an XML document doesn’t mean it’s The One True Description for that service. It’s just the most convenient one to generate for the app server on which the service is deployed.

One of the things that most hurts XML as an on-the-wire format is XSD. But not in the sense that “XSD is bad”. Sure, it has plenty of warts, but what really hurts XML is not XSD per se as much as the all-too-common assumption that if you use XML you need to have an XSD for it (see fat-bottomed specs, the key message of which I believe is still true even though SML and SML-IF are now dead).

I’ve had several conversations like this one:

– The best part about using JSON and REST was that we didn’t have to deal with XSD.
– So what do you use as your service contract?
– Nothing. Just a human-readable wiki page.
– If you don’t need a service contract, why did you feel like you had to write an XSD when you were doing XML? Why not have a similar wiki page describing the XML format?
– …

It’s perfectly fine to have service descriptions that are optimized to meet a specific need rather than automatically focusing on syntax validation. Not all consumers of a service contract need to be using the same description. It’s ok to have different service descriptions for different users and/or purposes. Which takes us to the next fallacy. What are service descriptions for if not syntax validation?

A service description does NOT mean you have to validate messages

As helpful as “validation” may seem as a concept, it often boils down to rejecting messages that could otherwise be successfully processed. Which doesn’t sound quite as useful, does it?

There are many other ways in which service descriptions could be useful, but they have been largely neglected because of the focus on syntactic validation and stub generation. Leaving aside development use cases and looking at my area of focus (application management), here are a few use cases for service descriptions:

Creating test messages (aka “synthetic transactions”)

A common practice in application management is to send test messages at regular intervals (often from various locations, e.g. branch offices) to measure the availability and response time of an application from the consumer’s perspective. If a WSDL is available for the service, we use this to generate the skeleton of the test message, and let the admin fill in appropriate values. Rather than a WSDL we’d much rather have a “ready-to-use” (possibly after admin review) test message that would be provided as part of the service description. Especially as it would be defined by the application creator, who presumably knows a lot more about that makes a safe and yet relevant message to send to the application as a ping.

Attaching policies and SLAs

One of the things that WSDLs are often used for, beyond syntax validation and stub generation, is to attach policies and SLAs. For that purpose, you really don’t need the XSD message definition that makes up so much of the WSDL. You really just need a way to identify operations on which to attach policies and SLAs. We could use a much simpler description language than WSDL for this. But if you throw away the very notion of a description language, you’ve thrown away the baby (a classification of the requests processed by the service) along with the bathwater (a syntax validation mechanism).

Governance / versioning

One benefit of having a service description document is that you can see when it changes. Even if you reduce this to a simple binary value (did it change since I last checked, y/n) there’s value in this. Even better if you can introspect the description document to see which requests are affected by the change. And whether the change is backward-compatible. Offering the “before” XSD and the “after” XSD is almost useless for automatic processing. It’s unlikely that some automated XSD inspection can tell me whether I can keep using my previous messages or I need to update them. A simple machine-readable declaration of that fact would be a lot more useful.

I just listed three, but there are other application management use cases, like governance/auditing, that need a service description.

In the SOAP world, we usually make do with WSDL for these tasks, not because it’s the best tool (all we really need is a way to classify requests in “buckets” – call them “operations” if you want – based on the content of the message) but because WSDL is the only understanding that is shared between the caller and the application.

By now some of you may have already drafted in your head the comment you are going to post explaining why this is not a problem if people just use REST. And it’s true that with REST there is a default categorization of incoming messages. A simple matrix with the various verbs as columns (GET, POST…) and the various resource types as rows. Each message can be unambiguously placed in one cell of this matrix, so I don’t need a service description document to have a request classification on which I can attach SLAs and policies. Granted, but keep these three things in mind:

  • This default categorization by verb and resource type can be a quite granular. Typically you wouldn’t have that many different policies on your application. So someone who understands the application still needs to group the invocations into message categories at the right level of granularity.
  • This matrix is only meaningful for the subset of “RESTful” apps that are truly… RESTful. Not for all the apps that use REST where it’s an easy mental mapping but then define resource types called “operations” or “actions” that are just a REST veneer over RPC.
  • Even if using REST was a silver bullet that eliminated the need for service definitions, as an application management vendor I don’t get to pick the applications I manage. I have to have a solution for what customers actually do. If I restricted myself to only managing RESTful applications, I’d shrink my addressable market by a few orders of magnitude. I don’t have an MBA, but it sounds like a bad idea.

This is not a SOAP versus REST post. This is not a XML versus JSON post. This is not a WSDL versus WADL post. This is just a post lamenting the fact that the industry seems to have either boxed service definitions into a very limited use case, or given up on them altogether. It I wasn’t recovering from standards burnout, I’d look into a versatile mechanism for describing application services in a way that is geared towards message classification more than validation.

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Filed under API, Application Mgmt, Everything, Governance, IT Systems Mgmt, Manageability, Mashup, Mgmt integration, Middleware, Modeling, Protocols, REST, SML, SOA, Specs, Standards

Don’t tell Facebook what you like, tell Twitter

There seems to be a lot to like technically about the announcements at Facebook’s f8 conference, especially for a Semantic Web aficionado. But I won’t have anything to do with it as a user. Along with the usual “your privacy is our toy” subtext, I really don’t like the lack of data portability. “Web 2.0” is starting to look a lot like “AOL 2.0”. Here is a better way to do it.

Taking the new “like” button as a simple example, I’d much rather tell Twitter what I like than Facebook. A simple #like hashtag in a tweet can be used to express positive feelings for what the tweet describes. Here is a quick list of the many advantages of this approach over the newly-introduced Facebook “like” feature.

It’s public

Your tweets are available to all. Your Facebook profile can still consume them, so if you think Facebook does the best job at organizing this information about you and your friends you can still go there to view the results. But other applications and networks can tap into the same data, so you can also benefits from innovation coming out of companies which do not want to be Facebook sharecroppers.

It’s publicly public

By which I mean that there is no pretense of privacy and no nasty surprise when trust is violated. Which is going to happen again and again. Especially when it’s not just a matter of displaying data but also of inferring new information based on the raw data collected. At which point it’s almost impossible to segregate access to the derived information based on the privacy settings of the individual data pieces. On Twitter, it’s all public, we all know it from the start, and as such we’re not fooled into sharing more than we should. See the fallacy of privacy settings.

It works on all things

Rather than only being on a web page, you can use a #like hashtag to describe any URI (dereferenceable or not) or even plain text. Just like RDF allows the value of an attribute to be either a URI or a scalar value (string, number…). For example, you can express that you like a quote or a verse of a poem by including them directly in the tweet. It’s not as identifiable as something that has a URI, but it can still be part of your profile. And smart consumers of this data might still be able to do some processing on it (e.g. recognizing it as a line from a song).

It can still be 1-click

You don’t necessarily have to copy/paste a URL (or text) into twitter. A web site can still do this for you, as long as it has your permission to post on your behalf. With that approach, it looks exactly like the Twitter “like” button to the user. You don’t have to be a Twitter user, just to have a Twitter account. No need for a Twitter client or to visit the Twitter web site if you don’t want to. It’s also OK if you have zero followers, Twitter is just a technical conduit in this approach.

It can evolve

The success of Twitter is also the success of self-organization as illustrated by the emergence of @replies, #hashtags and RT, directly form the users. Rather than having Facebook decide what verbs make sense to allow users to express their thoughts on the Web, let people decide and see what verbs emerge (e.g. to describe what you like, dislike, are curious about, are considering buying, etc). The only thing we need is an understanding that the hashtag qualifies the user’s attitude towards what’s described by the rest of the tweet. Or maybe hashtags should not be reused for this, maybe we need a new breed, “semtags” (semantic tags), with a different syntax, e.g. “^like”. This way you can semtag a hashtag, e.g. “^like #nyc” might replace “I ♥ NY” on twitter feeds (and tee shirts). It can be as simple or as complex as needed, based on what sticks in the real world. Nerds like me will try to qualify it (e.g. “^!like” for “I don’t like”) and might even come up with ontologies (^love subClassOf ^like). These experiences will probably fail and that’s fine. Evolution strives on failures.

It is transparent

Even if you let a site write these messages on your twitter feed, you can see exactly what goes on. There is no secret channel as with Facebook. The fact that it goes on your Twitter timeline acts as a validation, ensuring that only relevant, human-readable messages get added to your profile. Which is the only way in which we can maintain control of our profile information. If sites start to send too much information or opaque information you’ll see it. And so will your followers. This will put pressure on sites to make the posted data sparse and meaningful, because they know that their users won’t want to scare away their followers with social spam. See, for example, how the outcries over foursquare spam seem to have forced a clean-up (or at least so it looks to me, but maybe it’s just because I’ve unfollowed the spammers). Keeping social profiling on a human scale is a bug, not a feature.

It is persisted in many places

Who do you think is more likely to be around in 20 years, Facebook or the Library of Congress? Tweets are archived in many places, including Twitter itself, of course, but also Google, Bing and the Library of Congress. Plus, it’s very easy for you to set up a system to save all your tweets. Even if Twitter disappears, all the data in your profile that was built from your tweets will still be around. And if Google, Bing and the Library of Congress all go dark before Facebook, well that’s fine because the profile data from your tweets can be there too.

In effect, you should think of Facebook as a repository and Twitter as a stream. Don’t publish directly to one repository. Publish to a stream and benefit from all the repositories and other consumers that tap into it. It’s a well-known enterprise integration pattern (message bus), but it’s not just good for enterprise applications.

In fact, more than Twitter itself it’s this pattern that I want to encourage. Twitter is just the most obvious implementation, at this time, of a profile data bus. It already has almost everything we need (though a more fine-grained authorization model, or a delegated authorization model, would make me more likely to allow sites to tweet on my behalf). What matters is the switch from social networks owning data to you owning your data and social networks competing on how much value they can deliver to you based on the data. For example, LinkedIn might be the best for work connections, Facebook for personal connections, Google for brute search/retrieval of information, etc. I don’t want to maintain different profile data and privacy settings for each of them. I have one global privacy settings, which controls what I share with the world. Based on this, I want these sites to compete on the value they provide to me. It may not be what Facebook wants, but if what works best for us.

If you like this proposal, you know what you have to do. Go ahead and tweet:


Or just retweet it.

[UPDATED 2010/5/6: See the next post for some clarifications.]


Filed under Everything, Facebook, Google, Mashup, RDF, Semantic tech, Social networks, Twitter

Expanding on “twitter with a brain”

Chuck Shotton recently made a compelling case (“Twitter with a Brain“) for Twitter tools to allow the user to change the protocol endpoint. That is, instead of always going to, you can tell your Twitter client to send all requests to Why would you do this? You should read his blog entry, but in short his point is that the intermediary can add all kinds of new features that neither the Twitter client nor Twitter itself support. As always in computer science, a new level of decoupling adds opportunities for extensions (and breakage too, of course).

I fully agree with what he writes and I would very much like to see his call to action answered. In fact, I want more than what he is asking for. So here is my call to action:

1) It’s not just Twitter

Why just Twitter? This should be true for any client using any protocol. Why not also the APIs for the various Google and Yahoo services? The APIs for the other social networks beyond Twitter? For shopping sites like Amazon and EBay? Etc. And of course to all the various Cloud providers out there. Just because I am using the Amazon EC2 API it doesn’t mean I necessarily want the requests to go straight to Amazon. Client tools should always make the endpoint configurable, period.

2) It’s not just the clients, it’s also (and especially) the third party sites

Chuck’s examples are about features that the Twitter clients could provide but don’t, so an intermediary would be an easy way to hack support for them (others presumably include modifying the client – if open source -, writing a plug-in for it – it there is such mechanism -, or running a network interceptor on the local client – unless the protocol is encrypted-).

That’s nice and I’d love to see this, but the big deal for me is less with clients and more with third party sites. You know, all these sites that ask for your Twitter login/password. Or those that ask for your GMail/Yahoo account info to retrieve a list of your contacts. I never grant these requests, but I would consider it if they allowed me to tell them what endpoint URL to use. For example, rather than using my Twitter login to go straight to, they would use a login/password that I create and talk to The requests would be in the exact same shape as what they send today to Twitter, just directed to another URL. There, I could have a proxy that only allows some requests (e.g. “update twitter background image” but not “send update”) and forwards them using my real Twitter credentials. Or, for email accounts, I could have a proxy that allows requests that read my address book but not those that read my mails. The goal here is not to add features, it is to delegate trust in a fine-grained (and audited) manner. This, to me, is the burning need, rather than a 3rd place to implement Twitter lists.

I would probably write these proxies using a PaaS platform like the Google App Engine. Or maybe even Yahoo Pipes. I have long struggled to think of use cases for which Yahoo Pipes hits the sweetspot, and this may well be it. Especially if people write modules to handle specific APIs (e.g. a “Twitter API” module that shows all operations and lets you enable/disable them one by one in a pipe). The one thing missing would be a way for a pipe to keep a log of its invocations, for auditing.

You want access to my email and social network accounts? Give me the ability to filter you requests and you’ll get access. If it’s blind trust you want, I am afraid I have a very limited supply.

[Note: I wanted to add this as a comment on Chuck’s blog, but he doesn’t seem to allow them: “go start your own blog and/or shut up and eat your vegetables” is his recommendation. Since I already have my own blog, I guess I don’t have to eat my vegetables if I don’t want to. I just hope my kids don’t learn about this rule or they’ll be blogging in no time.]

[UPDATED 2009/11/30: WRT to Chuck’s request, it looks like it’s being done already. But no luck with the third party sites so far, which is what I most want to see.]


Filed under Automation, Everything, Google App Engine, Implementation, Mashup, PaaS, Portability, Protocols, Security, Social networks, Twitter, Yahoo

PaaS as a satisfying and success-ready hobbyist platform

I don’t know anyone in Silicon Valley who can code and doesn’t fantasize about writing an accidental killer app. One that gets designed during a long layover in DEN and implemented in a rainy weekend (El Nino is my VC). One that was only supposed to meet the needs of a few friends and is used by half of the world a few months/years later.

I am not talking about seasoned entrepreneurs, who have a network, discipline, resources and enough experience to know that it takes a lot more than a cool idea. Rather, about programming hobbyists (who may of may not be programmers in their day jobs),

By definition, hobbyists only do things that are satisfying. In the rarefied air of Silicon Valley, it also helps if there is a conceivable “upside” to dream about. Platform as a Service (PaaS, e.g. Google App Engine) provides both to software-oriented hobbyist. And make it very cheap (borderline free), which doesn’t hurt.


In a well-crafted PaaS environment, the development process and the result are both satisfying. I am not a Google shrill, but GAE is a fair example. The barrier to entry is very low (the download is less than 10MB and contains all you need to get started). In an hour you have an application running locally. In an hour and 5 minutes you have it deployed and accessible on the web for all. And yet this ease of bootstrap does not come at the cost of too many longer-term limitations (now that the environment has gown a bit from the original limitations and provides scheduled and background jobs). Unlike Yahoo Pipes, for which the first impression is “nifty!” and the second is “gimme a textual representation of my pipe now!”.

Beyond the easy ramp-up, the main source of satisfaction developing in a PaaS environment is that you spend 99% of your time working on the application. Not the OS, not the firewall, not the application container, not the database. Not to mention having to deal with your co-lo provider or the leased line for the servers in the basement. If you are a hobbyist with only a few spare hours per week, that’s a make or break deal. It also means that you have a fighting chance of developing a secure application because you are responsible for a much smaller surface of attack.

Eons ago (in computing time), Visual Basic was the name of the game for these people. More recent was the rise of PHP. It dramatically lowered the barrier to adoption and provided a quick route to a working web application. I know several non-professional developers (e.g. web designers) who are scared of any “normal” programming language but happily write PHP (often of equivalent complexity BTW). Combine this with the wide availability of ISP-managed PHP environments and you get close to what GAE gives you. At the risk of adding to the annoying trend of retroactively cloudifying everything, I think of ISP-hosted PHP as the first generation of PaaS. But it is focused on “show what’s in the DB” scenarios rather than service-centric / mash-up / web 2.0 integration. And even for DB-centric scenarios, by and large PHP coders don’t want to think too much about model and queries (and it shows). I think Google decided to go with Python rather than the easy route of aping the hosted PHP environments in large part to avoid hitting such ceilings down the road. Not surprisingly, PHP support is currently the most requested GAE feature, ahead of Perl and Ruby. Lets see if Google tries to get the PHP community on board or prefers to stay clear of such PaaS legacy (already!).

Ready for success

In the unlikely event that your application catches fire and sees wide adoption (which is not impossible, especially if well integrated in a social network), what are you going to do about it? Keeping in mind two constraints: first, this is a part-time hobby of yours. Second, don’t dream of riches. We are talking about an influx of facebookers or twitterers here, with no intention to pay for anything. But click they will. If you were going to answer: “I get funding and hire a real IT staff” then think again. You most likely won’t get funding for your toy app without revenue potential. And even if you do, by the time you have it it’s too late and people have moved on because you were not there when the spotlight was on you.

With a PaaS-based application you have a fighting chance. If the spike is short enough, you may not even hit the limit of the free quota. If it does, you have the choice of whether you are willing to pay to support the extra traffic or not. No change in code required (though it may be advised anyway, if your app wasn’t architected for efficient scaling – PaaS doesn’t entirely take this off your hands).

That “sudden spike” story is a commonly-invoked use case for EC2. And it’s probably true for a start-up with an IT staff (of at least one full-time person). But despite Amazon’s efforts (and other providers such as RightScale) this type of scaling is something you have to architect for and putting it in place takes away from the time you spend coding application features. It also means that you are responsible for more infrastructure (OS and application container at least). Not to mention that IaaS providers don’t usually offer free resources for limited usage, the way Google does (I suspect 99% of GAE apps never get over this quota). Even if a small EC2 instance is not very expensive (though it adds up over time if you keep it up for that occasional user), the difference between “free” and “cheap” is significant. As an application provider you’d like for this not to be the case with your users, but as a consumer of infrastructure service you’re on the other side of the deal, aren’t you?

There is a reason why suburbia-bound SUVs are advertised crossing mountain streams. The “I could if I wanted to” line has appeal. For the software hobbyist, knowing that your application won’t crash if it happened to meet success (even if only for a couple of days, e.g. the Slashdot effect) is a good feeling (“I could if *they* wanted to”). In truth this occasion is rare (and likely to end up like this), but you are ready for the eventuality. And if there are enough such hobbyists, then statistically some will encounter it.

The provider’s upside

That last point brings the topic of the PaaS provider’s upside in this. I have read several critical comments arguing that no company will rewrite their application for GAE (true) and that no start-up will write their new code for it either because of the risk of lock-in (also true: “being bought by Google” is not a bad outcome but “has to be bought by Google” is a bad exit strategy). But I think this misses the point of casting such a wide nest and starting with creating a great tool for hobbyists.

After all, Google has made a great business monetizing millions of small sites none of which makes much money by itself. At the very least least this can grow the web and, symbiotically, Google. With  two possible upsides:

  • Some of these hobbyist applications may actually take off and Google becomes their natural partner/godfather (including managing their user accounts). For example, wouldn’t it be nice for Google if Craigslist or Twitter was running on GAE?
  • The platform eventually evolves into something that makes sense for start-ups, SMBs and/or enterprises to use. Google works out the kinks with less demanding users first.

Interesting times

Two closing thoughts, which I’ll leave undeveloped for now:

  • There is an especially good synergy between mobile apps and PaaS. Once you get past the restaurant tip calculators, many mobile apps need a server-hosted sidekick to do the heavy lifting of gathering/storing/transforming data. As a hobbyist, you want to spend most of your time making you mobile app cool. Which leaves even less time for administrating server components. On the server side, you are even less likely to want to deal with anything but application logic. PaaS is especially attractive in these scenarios. Google and Microsoft have to navigate these waters carefully but look for some synergy/integration stories around GAE + Android and Azure + Windows Mobile respectively. Not clear what Apple’s story is here or if they think they need one. If it surfaces as an issue then we have yet another reason to restart the “Apple buys Adobe” rumor. Or maybe Sanjiva will get a middle-of-the-night call from Steve Jobs…
  • A platform to build/run your application is one thing. A way to reach users is another (arguably much more critical). Things like mobile app stores (especially Apple’s of course), Facebook and next generation app stores. But this goes  beyond the scope of this post.

Just to be clear, I am not in any way suggesting that PaaS is only for hobbyists. I am just saying that right now it is a great tool for them, the best way for an individual programmer to have fun and have an impact. This doesn’t take away from the value that PaaS will eventually deliver to larger organizations.

[UPDATED 2009/10/4: Microsoft Azure apparently supports PHP.]


Filed under Cloud Computing, Everything, Google, Google App Engine, Implementation, Mashup, Microsoft, PaaS, Utility computing, WSO2

REST in practice for IT and Cloud management (part 2: configuration management)

What benefits does REST provide for configuration management (in traditional data centers and in Clouds)?

Part 1 of the “REST in practice for IT and Cloud management” investigation looked at Cloud APIs from leading IaaS providers. It examined how RESTful they are and what concrete benefits derive from their RESTfulness. In part 2 we will now look at the configuration management domain. Even though it’s less trendy, it is just as useful, if not more, in understanding the practical value of REST for IT management. Plus, as long as Cloud deployments are mainly of the IaaS kind, you are still left with the problem of managing the configuration of everything that runs of top the virtual machines (OS, middleware, DB, applications…). Or, if you are a glass-half-full person, here is another way to look at it: the great thing about IaaS (and host virtualization in general) is that you can choose to keep your existing infrastructure, applications and management tools (including configuration management) largely unchanged.

At first blush, REST is ideally suited to configuration management.

The RESTful Cloud APIs have no problem retrieving resource descriptions, but they seem somewhat hesitant in the way they deal with resource-specific actions. Tim Bray described one of the challenges in his well-considered Slow REST post. And indeed, applying REST to these “do something that may take some time and not result exactly in what was requested” scenarios is a lot less straightforward than when you’re just doing document/data retrieval. In contrast you’d think that applying REST to the task of retrieving configuration data from a CMDB or other configuration store would be a no-brainer. Especially in the IT management world, where we already have explicit resource models and a rich set of relationships defined. Let’s give each resource a URI that responds to HTTP GET requests, let’s turn the associations into hyperlinks in the resource presentation, let’s mint a MIME type to represent this format and we are out of the office in time for a 4:00PM tennis game when all the courts are available (hopefully our tennis partners are as bright as us and can get out early too). This “work smarter not harder” approach would allow us to present this list of benefits in our weekly progress report:

-1- A URI-based scheme makes the protocol independent of the resource topology, unlike today’s data stores that usually struggle to represent relationships between stores.

-2- It is simpler to code against than CIM-over-HTTP or WS-Management. It is cross-platform, unlike WMI or JMX.

-3- It makes it trivial to browse the configuration data from a Web browser (the resources themselves could provide an HTML representation based on content-type negotiation, or a simple transformation could generate it for the Web browser).

-4- You get REST-induced caching and scalability.

In the shower after the tennis game, it becomes apparent that benefit #4 is largely irrelevant for IT management use cases. That the browser in #3 would not be all that useful beyond simple use cases. That #2 is good for karma but developers will demand a library that hides this benefit anyway. And that the boss is going to say that he doesn’t care about #1either because his product is “the single source of truth” so it needs to import from the other configuration store, not reference them.

Even if we ignore the boss (once again) it only  leaves #1 as a practical benefit. Surprise, that’s also the aspect that came out on top of the analysis in part 1 (see “the API doesn’t constrain the design of the URI space” highlight, reinforced by Mark’s excellent comment on the role of hypertext). Clearly, there is something useful for IT management in this “hypermedia” thing. This will largely be the topic of part 3.

There are also quite a few things that this RESTification of the configuration management store doesn’t solve:

-1- The ability to query: “show me all the WebLogic instances that run on a Windows host and don’t have patch xyz applied”. You don’t have much of a CMDB if you can’t answer this. For an analogy, remember (or imagine) a pre-1995 Web with no search engine, where you can only navigate by starting from your browser home page and clicking through static links step by step, or through bookmarks.

-2- The ability to retrieve the configuration change history and to compare configurations across resources (or to a reference configuration).

This is not to say that these two features cannot be built on top of a RESTful IT resource model. Just that they are the real meat of configuration management (rather than a simple resource-by-resource configuration browser) and that your brilliant re-architecture hasn’t really helped in addressing them. Does a RESTful foundation make these features harder to build? Not necessarily, but there are some tricky aspects to take care of:

-1- In hypermedia systems, the links are usually part of the resource representation, not resources of their own. In IT management, relationships/associations can have their own lifecycle and configuration properties.

-2- Be careful that you can really maintain the address of a resource. It’s one thing to make sure that a UUID gets maintained as a resource configuration changes, it’s another to ensure that a dereferenceable URI remains unchanged. For example, the admin server of a cluster may move over time from one node to another.

More fundamentally, the ability to deal with multiple resources at the same time and/or to use the model at different levels of granularity is often a challenge. Either you make your protocol more complex to account for this or your pollute your resource model (with a bunch of arbitrary “groups”, implicit or explicit).

We saw this in the Cloud APIs too. It typically goes something like this: you can address an individual server (called “foo”) by sending requests to Drop the “foo” part of the URL and now you can address all the servers, for example to retrieve their configuration or possibly to reboot them. This gives me a way of dealing with multiple resources at time, but only along the lines pre-defined by the API. What if I want to deal only with the servers that host nodes of a given cluster. Sorry, not possible. What if the servers have different hosts in their URIs (remember, “the API doesn’t constrain the design of the URI space”)? Oops.

WS-Management, in the SOAP world, takes this one step further with Selectors, through which you can embed some kind of query, the result of which is what you are addressing in your message. Or, if all you want to do is GET, you can model you entire datacenter as one giant virtual XML doc (a document which is never assembled in practice) and use WSRF/WSDM’s “QueryExpression” or WS-Management’s “FragmentTransfer” to the same effect. BTW, I have issues with the details of how these mechanisms work (and I have described an alternative under the motto “if you are going to suffer with WS-Addressing, at least get some value out of it”).

These are all non-RESTful atrocities to a RESTafarian, but in my mind the Cloud REST API reviewed in part 1 have open Pandora’s box by allowing less-qualified URIs to address all instances of a class. I expect you’ll soon see more precise query parameters in these URIs and they’ll look a lot like WS-Management Selectors (e.g. Want to take bets about when a Cloud API URI format with an embedded regex first arrives?

When you need this, my gut feeling is that you are better off not worrying too much about trying to look RESTful. There is no shame to using an RPC pattern in the right circumstances. Don’t be the stupid skier who ends up crashing in a tree because he is just too cool for the using snowplow position.

One of the most common reasons to deal with multiple resources together is to run queries such as the “show me all the WebLogic instances that run on a Windows host and don’t have patch xyz applied” example above. Such a query mechanism recently became a DMTF standard, it’s called CMDBf. It is SOAP-based and doesn’t attempt to have anything to do with REST. Not that it didn’t cross the mind of a bunch of people, lead by Michael Coté when CMDBf first emerged (read the comments too). But as James Governor rightly predicted in the first comment, Coté heard “dick” from us on this (I represented HP in CMDBf and ended up being an editor of the specification, focusing on the “query” part). I don’t remember reading the entry back then but I must have since I have been a long time Coté fan. I must have dismissed the idea so quickly that it didn’t even register with my memory. Well, it’s 2009 now, CMDBf v1 is a DMTF standard and guess what? I, and many other SOAP-the-world-till-it-shines alumni, are looking a lot more seriously into what’s in this REST thing (thus this series of posts for me). BTW in this piece Coté also correctly predicted that CMDBf would be “more about CMDB interoperation than federation” but that didn’t take as much foresight (it was pretty obvious to me from the start).

Frankly I am still not sure that there is much benefit from REST in what CMDBf does, which is mostly a query interface. Yes the CMDBf query and its response go over SOAP. Yes in this case SOAP is mostly a useless wrapper since none of the implementations will likely support any WS-* SOAP header (other than paying the WS-Addressing tax). Sure we could remove it and send plain XML over HTTP. Or replace the SOAP wrapper with an Atom wrapper. Would it be anymore RESTful? Not one bit.

And I don’t see how to make it more RESTful. There are plenty of things in the periphery the query operation that can be made RESTful, along the lines of what I described above. REST could make the discovery/reconciliation tasks of the CMDB more efficient. The CMDBf query result format could be improved so that from the returned elements I can navigate my way among resources by following hyperlinks. But the query operation itself looks fundamentally RPCish to me, just like my interaction with the Google search page is really an RPC call that happens to return a Web page full of hyperlinks. In a way, this query (whether Google or CMDBf) can at best be the transition point from RPC to REST. It can return results that open a world of RESTful requests to you, but the query invocation itself is not RESTful. And that’s OK.

In part 3 (now available), I will try to synthesize the lessons from the Cloud APIs (part 1) and configuration management (this post) and extract specific guidance to get the best of what REST has to offer in future IT management protocols. Just so you can plan ahead, in part 4 I will reform the US health care system and in part 5 I will provide a practical roadmap for global nuclear disarmament. Suggestions for part 6 are accepted.


Filed under API, Application Mgmt, Automation, Cloud Computing, CMDB, CMDB Federation, CMDBf, DMTF, Everything, IT Systems Mgmt, Mashup, Mgmt integration, Modeling, REST, SOAP, SOAP header, Specs, Standards, Utility computing

/me thinks Google Wave looks like IRC

If you’re not yet seasick with all the reviews of Google Wave, here are a few additional thoughts.

My mental picture for a Wave is that of an IRC channel on which each message is an edit to an XML doc. And where the IRC server (or a bot, like Zakim) keeps a log of all messages. I think it’s the use of bots in Wave as in IRC that pushed me towards this view. The character-per-character update reminded me of the arguments about the comparative values of the Unix “talk” command and IRC. And if the IRC comparison holds water, hang on for the upcoming bot wars. BTW, doesn’t this Wave Federation Protocol look like an ideal opportunity to resurrect the IRC bot attack code that leveraged server splits?

Leaving IRC aside, the other obvious lens through which to look at Wave is the good old WS/REST debate. Let’s brace ourselves for the “is Wave RESTful” analysis that are sure to follow. I’ll note, tongue in cheek, that an alternative (to XMPP) way to implement a Wave could be provided by the WS specifications currently being worked on in the W3C Web Services Resource Access working group : send a succession of WS-RT “Put” messages to a WS-Eventing event sink that, in turn, acts as an event source. Or formalize the sink/source combination more cleanly as a broker from WS-BrokeredNotification. Finally a non-management use case for these specifications! Good luck doing character-by-character updates over this, but I am not sure that this is the most fundamental part of Wave anyway (though it makes for a good demo).

Nick Gall is right to separate the “technology showcase” aspect from the “killer app” aspect. The demo is very nice but it takes more than cool technology to change years of habits and social conventions, supported by hundreds of tools. So I am not sure how much of a killer app this collaboration demo is, however nice. On the other hand, I can see how the underlying framework (or at least the techniques used to create it) could quickly spread. I need more time looking at the federation protocol to decide what I think about it. This blog entry clearly describes the three Ps (product, platform, protocol) and some of the history.

As far as how this may relate to systems management, I don’t see too much alignment from a modeling perspective. What really matters in IT models are the relationships between the entities and Wave puts a lot more focus on the content of each wave than its relationships with others. At least for now. The underlying synchronization techniques on the other hand seem more readily applicable. The Rasmussen brothers previously created Google Maps which I found very inspiring from an IT management point of view. Years later the IT management industry still hasn’t caught up with them.


Filed under Everything, Google, JavaScript, Mashup

Is notification wrapping getting a bum rap?

Looks like the question of whether to wrap SOAP-based notifications is back. Like Gil I prefer to stay away from wrapping notifications but my reasons are somewhat different.

I am not convinced by WSDL-centric arguments one way or the other. Proponents of wrapping say that it gives them a WSDL they can use for creating a generic listener, while opponents say that avoiding wrapping gives them a WSDL that generates useful code (payload-aware). I am not a big fan of WSDL-based code generation, but even if you are going to do it nobody says that you have to do it based on the WSDL document that ships with the specification. You’re free to modify the WSDL any way you want before feeding it to your code generation tool, as long as the result correctly describes the messages. One can write an infinity of WSDL documents for a given set of messages, some more precise and others more high-level (in which you quickly hit an xs:any). So, if the spec gives you a WSDL where the payload is xs:any and you know that in your case the payload is going to be sec:intrusionDetected, feel free to insert that element in the WSDL before running wsdl2java or whatever.

At the end, the question is not about what the WSDL in the specification looks like. The question is simply to what extent you know ahead of time the payload of the events you are going to have to handle. And you’d better know enough about the payload to create whatever logic your event consumer has to apply to the notification. Whether that’s through WSDL or some other mean. If you are not going to apply any payload-dependent logic (“generic sink”) then you don’t need to know anything about the payload. And I don’t see why someone needs a wrapper to create a generic sink.

Rather, what I don’t like about wrapping notifications is that you force them to be handled only as notifications, not as regular SOAP messages. You put them in a separate world and you make it hard for someone to create a service that can be invoked either in a subscription-driven way or in a direct way.

Here is a made-up example: consider a message to indicate that a physical intrusion has been detected in a building. There are many possible consumers for this message (local security staff, private security company, police, sound alarm, the cell phone of the owner, audit log, etc…). There are many possible sources for the message. In some cases, the message does not come from a subscription (e.g. a homeowner calls the security company and the operator enters data in a system that produces the message, or the sensor is hard-coded to sound the alarm). In others, there is a subscription (e.g. a home alarm system allows someone to register phone numbers and email addresses to which to send intrusion alerts). Sometimes something that starts as a subscription-based notification gets forwarded to someone who did not register for anything. It’s a good thing if web services that consume this message do not have to know (if they don’t care) whether this message originated because of a subscription or not. All they need to worry about is that there is a message that they have to respond to (e.g. by dispatching a patrol of clowns with orange lights on their car).

Here is a simpler analogy. Imagine that you have a filter in your email client to move all messages from Joe to a given folder. How much would you like to have to write the rule twice, one for messages that Joe sends to you directly and one for messages that Joe sends to a mailing list to which you are subscribed? Not very much I imagine.

At the same time, most notification systems are aware that they are processing notifications and there may be notification-related data that you’d like to have available in a consistent way (e.g. enough information to manage the subscription that resulted in you receiving this message). That’s fine but you don’t need an intrusive wrapper for this. Just use a SOAP header. It’s out of the way if you don’t care about it and it’s right there if you do (if you want to subject yourself to a two-year-old rant about how the SOAP processing model is unfortunately underutilized, be my guest).

One place where you need some kind of wrapping is when delivering several events at a time (either because you use pull-style retrieval or because you find it more efficient to push them in batches). If that’s what you’re after (and you want to handle it within one SOAP message rather than boxcarring a set of SOAP messages) then go ahead define a wrapper but make it a specialized wrapper that serves this purpose: collecting notifications and properly attaching whatever metadata to each. That’s a real purpose, not some WSDL make-believe.

Another use case is if you apply some transformation to the notification before sending it. Say that instead of returning a large notification you filter it by running an XPath on it and returning a serialization of the resulting node set (assuming you first solve the XPath serialization conundrum). You’d need some kind of wrapper to contain the result and put it in context, but again that should be a specialized wrapper for you filter mechanism. Not a generic wrapper.

It’s been a while since I really thought about this. My recollection may be flawed but I think I was already holding this position in the OASIS WS-Notification technical committee (which completed its work by publishing three standards in October 2006). I remember David Hull making a very eloquent case in the same direction (“wrapping” as policy-advertised option, not a part of the base framework), and strong pushback from IBM. I learned a lot about pub/sub systems from my WS-Notification committee co-chair, IBM’s Peter Niblett (a leading expert on the topic) while working on WS-Notification, but this is one area in which he did not convert me.

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Filed under Everything, Mashup, Mgmt integration, Middleware, SOAP, SOAP header, Specs, Standards, Tech

Oracle acquires ClearApp for composite application management

Oracle (and more specifically the middleware and applications management part of Oracle Enterprise Manager) has just acquired ClearApp. The company is based in Mountain View (California) and their QuickVision product is a very advanced management tool for composite applications, especially BPEL-based and Portal-based applications.

More information about the acquisition is available from this page and the press release. Information about the QuickVision product can be found on the ClearApp site.

QuickVision is a very complementary addition to our existing products and the acquisitions that we have made over the last year in the application management domain. Let’s take a performance management use case to see how they relate to one another conceptually (this is not an integration roadmap, just a comparison of the features of the existing products): Oracle Real User Experience Insight (from the Moniforce acquisition) will tell you that your users are seeing a performance degradation for a specific function of your Web application. If this is a stand-alone Java application, you can go straight into the Enterprise Manager App Server Diagnostic Pack to start from a URL and analyze where processing time is spent (servlet, JSP, EJB, JDBC…). AD4J (from the Auptyma acquisition) provides deep insight into the JVM. It will give you the line number and call stack of the slow methods. For example, it might lead you to a specific database call that is taking a long time to return. You can then follow the trail deep into the database using the Oracle Database Diagnostic and Tuning packs.

But if your application is a composite application (for example one that makes use of a BPEL process to orchestrate services deployed on different application servers), then you would have a hard time finding which application server to focus on. The QuickVision product fills that gap, taking a BPEL process from its invocation point into all its successive steps and into the code that the different steps invoke. So you can see if the problem is within the BPEL execution (e.g. you loop too many times) or inside an invoked Web service. In that case, QuickVision will lead you to the class that implements that service, at which point you have all the context that you need to fire off AD4J and do a fine-grained analysis of the problematic Java code as described above.

In this scenario (and assuming that the root cause is the slowness of a database query executed by a web services that has been invoked through a BPEL process), the chain of management capabilities goes something like this:

User Experience Insight
    -> QuickVision
        -> App Server Diagnostic Pack
            -> Database management packs

A variation on this would be if the service monitored was a SOAP service as opposed to a Web page. Oracle Web Services Manager could then be used as an alternative to Real User Experience Insight to alert you that something was amiss with the application performance. The rest of the flow would be the same.

At the end, it’s not just about managing Web services or Web sites, it’s about managing the whole SOA application.

Of course, QuickVision is not limited to performance analysis, even though that’s my favorite feature. For example, I could have picked a dependency analysis scenario.

To my new colleagues joining us from ClearApp, welcome!

[UPDATED 2008/9/9: InfoQ coverage of the acquisition by Dilip Krishnan.]


Filed under Application Mgmt, BPEL, Business Process, Everything, IT Systems Mgmt, Manageability, Mashup, Mgmt integration, Modeling, Oracle

WSO2 Mashup Server

I see that WSO2 has just released version 1.0 of their Mashup Server. Congratulations to Jonathan and the rest of the team. I haven’t played with the earlier betas of the Mashup Server but I have read enough about it to be interested. Now that it’s been released, it might be a good time to invest a few hours to look into it (I just downloaded it and I filled a small documentation bug already). I know (and like) many of the WSO2 guys (Jonathan, but also Sanjiva and Glen) from the early days of the W3C WSDL working group. Plus, you have to give credit to a company that offers visibility on its web site not just to its board and management team but also to its engineers.

But the Mashup Server is not interesting to me just because I know some of its authors. There are tow more important reasons. One is that it is the integration product in WSO2’s portfolio that is the most different in its approach from the many integration products in Oracle Fusion Middleware. We want Oracle Enterprise Manager to do an outstanding job at managing Oracle Fusion Middleware, but we also want it to manage other integrations approaches as well (we manage Tomcat for example). At this point there is of course no market demand for managing WSO2’s Mashup Server, but from an architectural perspective it’s a good alternative to keep in mind along with the BPEL, ESB, ODI, etc that are already in heavy use. I am always interested in perspectives that help make sure that the most abstract application/service management concepts remain suitably abstracted, so learning a bit about the Mashup Server can’t hurt. I’ll know more once I’ve looked at it, but my impression is that the Mashup Server is somewhere between BPEL and Ruby on Rails (or TurboGears) in terms of declarativity and introspectability (yes I like to make up words) for management purposes.

This may well be sweet spot and it’s my second reason for being interested in the Mashup Server. I am always interested in tools that help with quick prototyping and the best tool is different for each job. The Mashup Server is pretty unique and I can imagine it being a nice tool for some management integration prototypes once the participating services have been suitably XML-ized (something that that Oracle Fusion Middleware makes easy).

Interestingly, the release of this JavaScript-based platform comes on the same day that Joe Gregorio declares JavaScript to be the new SmallTalk.

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Filed under Everything, JavaScript, Mashup, Mgmt integration, Tech, WSO2