Saturday, December 15, 2007

Book Review: Loosely Coupled - The Missing Pieces…

This is a review of the book "Loosely Coupled: The Missing Piece of Web Services", by Doug Kaye. In a previous posting I expressed delight that an author had dedicated a book to this important topic. This perhaps is not the definitive book on loose coupling but there is plenty of value for the reader.

Doug has an easily readable style and sticks to a high level but there is enough technical substance to keep and IT architect or IT manager interested. You will find no code snippets and no programming standard specifications described in this book but there are some good diagrams and deep insights into SOA and how an organization should deliver SOA.

This book was published in 2003 and I kept expecting the information to be dated. There was no mention of an Enterprise Service Bus (ESB) but Doug Kaye describes a number network models, mediation tools and deployment options which have been incorporated into what vendors now label as an ESB. More importantly some of the missing pieces he describes in 2003 are still missing at the end of 2007. Security, transaction integrity and business semantics still do not have accepted solutions within SOA and these missing pieces are described in this book. The WS-* standards have progressed somewhat since the writing of "Loosely Coupled" but basics of SOAP, WSDL and UDDI were in place and many for the WS standards are foretold.

Doug has good perspective on what is required in the corporate world. He advises everyone to have your "elevator pitch" ready for that occasion when the CEO gets into the elevator with you and asks something like "So what's this I keep hearing about web services? What are they and why are they so important" (p27). Doug offers a response that suggests he is either a fast talker or works in a building that is much taller than mine, but the concept of having something ready like this is important if you are going evangelize about web services.

There is only one chapter dedicated to Loose Coupling and Doug has not tried to say everything there is to say on the subject. This justified in his statement "…loose coupling is a methodology or style, rather than a set of established rules and specifications" (p. 131). Figure 10-1 provides a table describing 10 types of coupling and descriptions of tightly and loosely coupled approaches to each. This is a good approach as it is not easy to describe coupling succinctly. I found this approach in another posting although interestingly the contents are different. I have found that in my previous posting that it is difficult to label types and coupling and the three column approach will enable me to do this more effectively. The book covers late binding, heterogeneity, routing and transformations well.

It is true to say that this book is more to do about its subtitle "The Missing Pieces of Web Services" than Loose Coupling. Doug makes the bold prediction that when we have solved all the pieces of the puzzle in the future that it will be so commonplace that "Web services won't be mentioned by the IT trade press, and the topic won't be tracked by analysts". The book searches through these missing pieces in most of the chapters. The fact that Web Services is still a strong topic for analysts and vendors is evidence suggesting that we have not yet found all those missing pieces.

Doug Kaye provides a good description of transaction control although I found the book I read earlier by Krafzig et al to have more detail in this area. Doug has two strong chapters on the problems of web services security and covers this topic in a thorough and systematic way. A couple of reviews have suggested that the book by Mark O'Neil also provides good coverage of Web Service security.

The chapter on deployment option talks about commercial opportunities for third parties in the delivery of services and services infrastructure. This discussed Web Service Networks, Distributed Web Service Networks, Web-Service Delivery Networks and Web Service Providers. Doug takes the service vendor view in his final chapter on providing external services. Both these chapters had little relevance to me. Four years after this book was written I have not been flooded with vendors wanting to sell me services or wanting to host infrastructure for me to operate my web service applications. Perhaps the money is not there, or perhaps it is just easier to use open source products or set up our own infrastructure. I still think Web Services provides some opportunities for commercial intermediaries, but until the vendors are out there and dealing in the government sector it will be difficult for me to get excited about this topic.

Doug writes a couple of good chapters on the management of simple and complex web services projects. In particular he deals with timing the project around web services approaches that have not yet been delivered. The chapter on Service Level Agreements (SLAs) was an important piece of the completion of the web services picture.

The book concludes with a number of checklists that anyone embarking on an SOA project should refer to. This should help the SOA project manager get their ducks in line to navigate the difficult road ahead.

In summary, this was a well written book about the evolving phenomenon of Web Services. There are some valuable insights into Loose Coupling but an exhaustive technical treatment of coupling and the programming patterns that can reduce coupling is out of the scope of this book. There are some important insights to be found, especially on the subjects of security, evangelizing and commercial arrangements. I expect I will refer to this book many times in the future.

Loosely Coupled: The Missing Pieces of Web Services, Doug Kaye ; RDS Press 2003, ISBN 1881378241

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