Wednesday, October 16, 2002

WS DevCon: Yasser Shohoud: The Right Way to Build Web services Yesser delivered a clear message, true for anyone building component-oriented software – nail the interfaces first, then think about internal component design. In Web Services world this practice is also applicable. One should start with WSDL first. Then design service internals using classes and data structures. Point taken. There’s little support in “developer tools” for this kind of workflow, so Yesser have called upon the audience to write their congressman and demand better “tools”.  By “tools” Yasser really meant VS.NET and seemed to brush off the reminders from the audience that there are in fact other developer tools that do support WSDL-first workflow. Being firmly in VS.NET camp, I nevertheless wasn’t impressed with the way Yasser made VS.NET the center of the world of dev tools.   WS DevCon: David Seidel & Mark Ericson:  Web Services Diagnostics David and Mark gave some good tips of how to ease debugging web services. Some of the tips: -          Use HTTP headers to transport logging messages -          Always compare cashed WSDL with the original to make sure that the other end is still using the same definition They also gave a demo of SOAPscope (looks like very interesting product). Contrasting with the previous speaker, they gave generous information about other diagnostic tools out there, including their direct competitors. Some of the tools I’ve noted: proxyTrace, xmldiff   WS DevCon: Andres Aguiar : DeKlarit Demo DeKlarit seems like a truly useful product, especially for people who are can start an application with a brand new database schema (as oppose to build an application on top of existing database). The design of the product and the way it integrates in VS.NET is very well done as well. Detailed product review by Chris is here.      WS DevCon: Don Box: What’s in a Name: Types and semantics in a web service universe Brian has a good account of this talk, so won’t repeat it.   I find it hard to crystallize key messages of this talk. Don seemed to spend most of his slot making an elaborated preamble and we out of time before delivering the key message. I think he wanted to explain how to achieve compatibility of types with XML Schema and  WSDL. XML Schema allows in fact substitutions of one type with another ‘compatible’ type using substitutionGroup attribute. How to use it with WSDL isn’t clear to me.      WS DevCon: Panel Here are some bits of the panel discussion I had time to jot down (lots of detail missing). Q: Thoughts on denial of service attack against Web Services? A: (Noan, Tim, Clemens): There’s no simple answer. SOAP makes such attacks easier to do and harder to protect against. To some extent, DOS is better solved at the network infrastructure level. When the flood of request hits your SOAP server, its probably too late. Q: Why does Microsoft has two SOAP stacks? A: (Don, carefully choosing words) Msft will make it really really simple to choose one over the other. [Read this any way you like…] Q: Any performance metrics that compare Axis against .NET SOAP? A: (Glen, Don) Axis is much faster than Apache SOAP. .NET Remoting is the fastest tech for distributed apps. Q: How valuable it is to become Web Services expert? A: (Don, others) In 5 years WS experts will be as valuable as TCP/IP expects today. Unless you work for msft .net group or other “plumbing shop” there will not be much opportunity to makes loads of money. Q: Why don’t we see lots of commercial public WS out there? A: (Don, Sam, others) MSN will have more consumer oriented with future releases (ex: mappoint) Most of the WS implementation will be done in the context of enterprise in-house developments, which in fact constitutes the majority of current and future software projects.      WS DevCon: Christopher Dix: .NET, XSLT and Web Services In my view, Chris has presented a truly original way to use XSLT and to build Web Services. The idea is simple. Fundamentally, a Web Service is nothing more than a processor that takes XML input and generates XML output. XSLT is a language to define transformations of one XML document in to another. If one thinks about WS and XSML in these terms, they are indeed pretty close. As Don put it “SOAP is XSLT with a longer wire”. So what Chris did was to create a Web Service almost entirely in XSLT. I say “almost” because you still need to write basic plumbing (HTTP listener, trigger XSLT) in “regular” code. The question is: how is it useful? After his talk I’ve bounced an application idea with Chris and others. I started thinking about how to expose inference engines and/or expert systems as Web Services. This problem is coming from the product I’m working on. Any application that is based on inference engine (such as CLIPS) is defined in terms of ‘facts’ and ‘rules’ about those facts. If one can find a mapping between CLIPS rules and XSLT templates; as well as mapping between CLIPS facts and SOAP messages – then you might have a generic WS interface to any inference engine application. That would be pretty cool. Now, I don’t pretend to know how to build such mapping. But I promised Chris I’ll spend some time thinking about it :)      WS DevCon: Scott Seely: Using inheritance with WS Scott has shown a design pattern that allows people to use class inheritance with classes that implement web services. I did not grasp all the fine details of the code and unfortunately I can’t find the code examples on Scott’s site. But from what I remember, he’d end up with a base class that would dispatch calls to sub-classes based on the type information found in WSDL. For many sub-classes you would end up with unmanageable switch-case construct. Then again, maybe I just didn’t get it…      WS DevCon: Noah Mendelsohn: XML Schema what you might not know (and might or might not like!)   Apart giving an overview of the finer points of XML Schema language Noan made a very interesting point about the spec: XML Schema is not just for XML documents. It was designed to be a generic language to describe data structures. So far, the usual use-case is to use it to define the structure of XML document. Noan made it very clear that nothing in the spec restricts its usage to describe data schemas held in other mediums such as in-memory representation, relational database, etc.   After the talk I’ve asked Noah is he knew if XML Schema is already being used beyond XML. I was specifically interested to know if databases would support XML Schema as a way to define the database schemas. Turns out, major DB players (DB2, SQL Server, Oracle) have fact started to work on it.   Memorable quote: “There is no such thing as simple feature”

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