Develop .NET Web Services Contract First with Christian Weyer's WSCF VS Add In

Hats off to Christian Weyer for creating his WSCF 'Web Services Contract First' tool to help provide Visual Studio tool support for building web services by starting with the XML schema and then generating the code.

The key to creating interoperable web services is to ‘build from the centre out’ and start by designing the messages that will be exchanged on the wire (the contract) and then work back to the implementation model that is used at the sender and receiver.  There are two basic approaches to building web services 'contract first' in .NET: code-based or schema-based.  The first approach is to start with the code and add Webmethod and XML Serialization attributes and allow .NET to generate the 'contract' (the WSDL file).  The second apporach involves XML Schema first and using this to create the WSDL file and generate the code, which happens to be Simon Guest’s number 1 recommendation for building interoperable web services.  Visual Studio has good support for the code-based approach to web service design, but up to now hasn't provided much support for the XML Schema approach.  This is where Christian’s WSCF tool comes in.

The tool performs two key tasks.  Firstly, the WSCF tool allows you to create the WSDL file from an XML Schema that describes the web services message.  Secondly, the WSCF tool can generate the code for the client- and server-side web services proxy classes that can be called from your .NET code.

Christian has a useful walk-through that illustrates how the WSCF tool can work.  The steps include:

• Using the Visual Studio XML Editor to create a schema for the data or entities that will be used in the web services messages.
• Creating a second schema that models the messages that will be sent and received by the web service.  This is done by imports the first schema file (using xs:import).  I liked keeping these two schemas separated using this technique.
• Using the WSCF tool to take this second schema and match up the web service operations with the messages to create the WSDL file.  I like that this step highlights the availability of Request/Response and One-Way message exchange patterns.
• Using the WSCF tool to create client- and server-side proxies from this WSDL file (including supporting public properties, serializable classes and collections).

As well as being a VS plug in the tool can also be run from the command line, making it easy to run as part of build process for instance.

While not everyone will want to design web services starting from the XML Schema, for those that do this tool will be a useful timesaver.  It also helps drive home the concept that web services are about messages and not objects.

Christian spoke about this tool and the general ‘contract first’ approach at a recent INETA-sponsored presentation at IrishDev.  You download the slides as well as reading good summaries from Marcus Mac Innes Contract First, Guinness Second as well as Keiran Lyman with Contractual Obligations (or, 'First Contact with Contracts').