There's an article on InfoQ entitled "Code First" Web Services Reconsidered which begins
Are you getting started on developing SOAP web services? If you are, you have two development styles you can chose between. This first is called “start-from-WSDL”, or “contract first”, and involves building a WSDL service description and associated XML schema for data exchange directly. The second is called “start-from-code”, or “code first”, and involves plugging sample service code into your framework of choice and generating the WSDL+schema from that code. With either development style, the end goal is the same – you want a stable WSDL+schema definition of your service. This goal is especially important when you’re working in a SOA environment. SOA demands loose coupling of services, where the interface is fixed and separate from the implementation.
With either development style, the end goal is the same – you want a stable WSDL+schema definition of your service. This goal is especially important when you’re working in a SOA environment. SOA demands loose coupling of services, where the interface is fixed and separate from the implementation.
There are lots of problems with this article, the main one being that choosing between “contract first” and “code first” SOAP Web Services development styles is like choosing between putting a square peg in a round hole and putting a round peg in a square hole. Either way, you will have to deal with the impedance mismatch between W3C XML Schema (XSD) and objects from your typical OO system. This is because practically every SOAP Web service toolkit does some level of XML<->object mapping which ends up being lossy because W3C XML Schema contains several constructs that don’t really map well to objects and objects may contain constructs that don’t really map well to W3C XML Schema depending on your platform choice.
The only real consideration when deciding between “code first” and “contract first” approaches is whether your service is concerned primarily with objects or whether it is concerned primarily with XML documents [preferrably with a predefined schema]. If you are just moving around data objects (i.e. your data model isn’t much more complex than JSON) then you are better off using a “code first” approach especially since most SOAP toolkits can handle the basic constructs that would result from generating WSDLs from such types. On the other hand, if you are transmitting documents that have a predefined schema (e.g. XBRL or OOXML documents) then you are better off authoring the WSDL by hand than trying to jump through hoops to get the XML<->object mapping technology in your off-the-shelf SOAP toolkit to do a great job with these schemas. Unfortunately, anyone consuming your SOAP Web service who is using an off-the-shelf SOAP toolkit will likely have interoperability issues when their toolkit tries to process schemas that fully utilize a significant number of the features W3C XML Schema. If your situation falls somewhere in the middle, then you’re probably screwed regardless of which approach you choose.
One of the interesting consequences of the adoption of RESTful Web services is that these interoperability issues have been avoided because most people who provide these services do not provide schemas in the W3C XML Schema. Thus discouraging the foolishness of XML<->object mapping based on XSD that causes interoperability problems in the SOAP world. Instead, most vendors who expose RESTful APIs that want to provide an object-centric programming model for developers who don’t want to deal with XML either create or encourage the third party creation of client libraries on target platforms which wrap their simple, RESTful Web services with a more object oriented facade. Examples of vendors who have gone with this approach for their RESTful APIs include
That way XML geeks like me get to party on the raw XML which is in a simple and straightforward format while the folks who are scared of XML can party on objects using their favorite programming language and platform. The best of both worlds.
“Contract first” vs. “Code first”? More like do you want to slam your head into a brick wall or a concrete wall?
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