SOA recommendations for an SME

Here are some of the recommendations an SME should follow if it is toying with the idea of SOA and doesn't want to come to grief.

• SOA advantages of speed-to-market, reduced cost, reuse, better business-IT alignment, better and faster decision makings have to be tempered with awareness of high implementation failures, increased governance and long-term commitment (Guah,2008,pp139-40). Practitioners advise making governance a priority and ‘think big but start small’ (Sumar,2008).

• REST currently is religion for many who prophesise demise of WS-* and consider this ‘second generation’ style offers better maintenance, performance, scalability, extensibility, simplicity, security and condemn SOAP RPC as ‘DCOM for the Internet’ (Prescod,2002). SOAP uses POST to send its payload so the results cannot be cached thus thwarting scalability. If you are dealing with images then be aware that mashup with image galleries like Flickr is easier with REST (Simpkins,2009,p6). SOAP demands an image payload be packed using base64 encoding while REST allows image to be retrieved as a resource. If the business handles images and has CRUD-like interactions then Restful services commend themselves.

Although lightweight REST architectural style is deemed simpler and leverages existing HTTP protocol with intuitive resource-based URIs for web services and Amazon sees 80% REST and 20% SOAP usage (Anderson,2006), we should adhere to WS-* standards as the trading partners are likely to be using it and expect it. The standardisation, flexibility, reliability, ESB-support and ubiquitous toolkits offering productivity enhancements are compelling argument for SOAP-based services (Simpkins,2009e,p5;Haas,2005). Web services orchestration using process-modelling language, BPEL, require WSDL contract so BPEL cannot be used with Restful services (Simpkins,2009,pp5-6).

A compromise of using both approaches will not be possible for SME as supporting both styles stretches IT skill-base and investment. SOAP solution offers the benefits of large historical investment by standards bodies, tool suppliers, governments and business users and is currently more versatile so recommended despite its need for higher infrastructure investment. The WS-* standards are likely to win in the longrun (Simpkins,2009,p6).

• Protect existing investment by building adapters for legacy applications. Various wrapping approaches are available to expose the functionality (Al-Belushi and Baghdadi,2007).

• Use document/literal wrapped as the encoding model for WSDL as it is most versatile and WS-I compliant (Butek,2005).

• An Eclipse IDE with plugins, jUDDI, MySQL and Tomcat open-source environment is fit for cheap experimentation and implementation without incurring huge licensing costs of commercial products. Apache Synapse ESB can be considered. Eclipse support both SOAP and Restful services.

• Discover domain-specific services and build relationship with suppliers rather than construct everything internally. For example, banks may provide currency conversion service. Publish selected internally developed services in public UDDI to expose image catalogue and win business.

Although many other aspects can be discussed but this should give a head start with tool selection and provide a handle on rather fanatical SOAP vs REST debate.

References

Al-Belushi W. and Baghdadi Y. (2007) ‘An Approach to Wrap Legacy Applications into Web Services’, Proc. Int'l Conf. Service Systems and Service Management (ICSSSM '07), pp.1-6, June 2007.

Anderson, T. (2006) 'WS-* vs the REST', Reg Developer, 26 April [online], http://www.regdeveloper.co.uk/2006/04/29/oreilly_amazon/ (accessed 3 June 2009)

Butek, R. (2005) Which style of WSDL should I use? [online], IBM, http://www.ibm.com/developerworks/webservices/library/ws-whichwsdl/ (accessed 3 June 2009)

Ghah M. W. (2008) Managing Very Large IT Projects in Businesses and Organizations, Idea Group, Pennsylvania

Sumar S. (2008) Making Your SOA Journey Successful – Key Aspects [online], Infosys, available at http://www.infosysblogs.com/soa/2008/08/making_your_soa_journey_succes.html (accessed 3 June 2009)

Prescod, P. (2002) Second Generation Web Services [online], O'Reilly Media, Inc., http://webservices.xml.com/pub/a/ws/2002/02/06/rest.html (accessed 3 June 2009)

Simpkins, N. (2009a) ‘Block 3 part 5: Web services messaging with HTTP’, in T320 E-business Technologies: Foundations and Practice, The Open University, Milton Keynes