Best Practices Guide for Documenting WSDL-based Web Services

This guide provides a set of best practices that will help you with the task of documenting a web service that is defined by a WSDL.  These best practices were established by the developers at Adivo who have extensive experience in technical documentation, web services design and development.

Start With a Good Web Service Design

A good design can make documenting your web service a much easier task.   Although it might not always be an option, if you have any influence over the design, here are some key areas that you should look out for:

  • Naming conventions - The lack of naming conventions can result in very inconsistent and cryptic names for the methods and parameters exposed by your web service making it more difficult to document them properly.  Applying good naming conventions to the web service API will promote better readability of the documentation.
  • Global components - WSDL supports the use of XML Schema Definition (XSD) elements and types to define method arguments. These schema components can be defined either locally within the parent component or globally so that the component can be reused. By using global components in your web service, you will maximize reuse and reduce the number of components that you need to document.

And even if you do not have any control over the design, a quick review will help you better estimate how much time it will take and set expectations for the completion of the documentation.

Embed Comments inside Your WSDL

The WSDL documentation tag can be used to add comments to methods and arguments, while the XSD annotation tag can be used to add comments to schema components. Both of these types of comments can be included as part of the web service definition making them easy to maintain as the WSDL changes over time.

By embedding comments inside your WSDL, you create a "self-documenting" web service definition that will be easier to understand.

Comment What You Can and Annotate Everything Else

To document your WSDL, you should add comments to the following web service components:

  • Methods - Methods are typically named as verb phrases that denote some type of operation or process that the method performs.  When you add comments to methods, describe what that process does.
  • Method Arguments - Methods can have zero or more input arguments and zero or more output arguments. For input arguments, describe what the argument represents and how it is used by the method. For output arguments, describe what the argument represents and how it was provided by the method.
  • Schema Components - Schema components such as elements and types are used to define input and output arguments. While some arguments may be defined by simple types like strings and numbers, other arguments may have a complex structure defined by a schema element or type. Providing descriptions of the schema components used to defined arguments allows you to document the structure of those arguments.

The descriptions that you add to these web service components should be concise and consist of one or two sentences.  If there is additional information that is important to document, you should consider structuring your comments into two parts: a summary description followed by a remarks section.  The remarks section can be used to include the additional information.

Although the commenting capabilities within the WSDL are quite robust, you may not want to include all of the information that you need for documenting the service in the WSDL itself in order to keep its size to a minimum.  If this is the case you can use a tool like TechWriter to annotate the web service with external comments that can be merged together with the embedded comments to produce the complete documentation.

Use a Documentation Generator

Having a self-documented web service is helpful for web service design and maintenance, but there are many instances where you are going to need actual API documentation. Here are a few examples:

  • Design Documentation - If you are creating a web service for a client, design documentation is typically a required deliverable.
  • Web Service API Documentation - While your web service developer may have the knowledge and expertise needed to read and understand a WSDL, developers that wish to make calls to the web service API may not.  You will need to provide these developers with some form of documentation that will help them use the API. 
  • Design Reviews - Not all participants in a design review are going to have the same level of web service knowledge and expertise.  Your subject matter experts may not be technical at all.  To facilitate such a design review, you will need to provide documentation that anybody can read and understand.

Fortunately there are tools like TechWriter that can be used to generate the web service documentation automatically, leveraging the web service definitions and the comments you've embedded.

Make Documentation Part of Your Development Process

If your project is using automated build tools like Ant, NAnt and MSBuild, you can make generating the documentation part of the automated build process for the system.   By having the documentation as up-to-date as the system itself, your project will benefit in the following areas:

  • Knowledge Capture - While some development methodologies such as Agile ascribe to a "document late" philosophy, projects can suffer greatly when they lose a team member.  The knowledge of a system literally walks out the door.  Documenting as you go minimizes the impact of losing a team member and makes it easier for new team members to ramp up.
  • Communication - Documentation can help communication among project team members.  The project manager can better assess the status of the project.  Subject matter experts can verify that developers are on the right track.  And mistakes can be identified earlier in the project life-cycle.
  • Documentation Quality - Scrambling at the end of the project to throw the documentation together for the final deliverable can result in the API not being documented properly, if documented at all. 

By making documentation part of your development process you will ensure that the documentation is always in sync with the web service, even in extreme programming environments where the WSDL is constantly changing. 

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