Web Services Abuse

Web Services is arguably one of the most significant advance in enterprise software systems in the last 5 years. Web Services have provided a mechanism to unlock and expose data and business logic buried within legacy systems in a uniform and standardized fashion. This is significant because most enterprises use a multitude of different software systems for various operational and strategic functions. These systems tend to be very different in their architectures, platforms, programming languages, interfaces and data stores. Web Services has made it is possible to have a single standard mechanism to access all systems.

Business processes in enterprises often involve accessing more than one system and require information flow among different systems. With Web Services-based standardized programmable access to all systems, we now have an opportunity to create so-called "composite applications" which allow seamless transfer of data and invocation of business logic across multiple systems.

SOAP is an important standard for Web Services. While the simpler REST-based Web Services are popular, SOAP is important in Web Services where security and reliability are important. For both SOAP- and REST-based Web Services, XML is the de facto standard for the format in which data is produced and consumed by services. This text-based format with a standardized and well understood structure is one of the reasons for the easy adoption of Web Services.

While Web Services is a great choice for enterprise system integration, it is also widely used where it probably shouldn't be. The primary scenario where Web Services is not the best choice is when it is used to integrate sub-systems within a system built by the same vendor, and in particular when there is a large amount of data transfer among these sub-systems. Often sub-systems owned by different development sub-groups are built independently without attempting to standardize on common infrastructure and inter sub-system service contracts. This is typically a result of development groups growing unmanageably large (see A Few Good Men) and sub-groups inherited from mergers and acquisitions. Each sub-system tends to adopt its own architecture, frameworks, metadata and data formats, and access mechanisms, ending up looking very different even though they may all be part of the same product suite sold by the same vendor. When it comes time for these sub-systems to talk to each other, the challenge is easily addressed with the magic words - Web Services. Each sub-system builds a Web Services layer and now they can all talk to each other fine. Problem solved. In reality though, there is a great deal of inefficiency in this approach. Often these sub-systems live in the same runtime and communication among them does not involve crossing process boundaries. In these cases, what should be simple co-located service API calls exchanging objects between sub-systems, becomes an inefficient process with unnecessary penalty of protocols such as SOAP and the overhead of XML processing. XML is by nature verbose and parsing of XML is expensive even with modern parsers. When the volume of data is large, the performance overhead of object->XML->Object transformations can be very significant. Data exchanges in binary format are typically orders of magnitude more efficient that text-based formats. This study illustrates graphically a benchmark that support this argument.

The need for loose coupling among sub-systems is often cited as a reason for integrating them through Web Services. The specious argument goes like this - if two sub-systems expose APIs and share object models, any change to one sub-system will require re-compilation of the other which is undesirable. However, what is often overlooked is that even with Web Services, if the format of the XML data produced by a service changes, the consumer of the XML has to re-work the business logic code requiring re-compilation and re-deployment.

The right paradigm for designing systems is to adopt the M13 services paradigm. All business functionality is thought of in terms of services. Services do not necessarily mean Web Services. One defines Java service interfaces that produce and consume serializable Java objects, and builds their implementations. This should be independent of how the services are exposed and invoked. An external declarative provisioning mechanism is available that dictates the best mode of service consumption - plain Java APIs, Web Services, EJBs etc. The underlying infrastructure insulates the author of the service from the provisioning and lets him/her focus on the service contract and business logic. It also allows for employing the optimal service invocation mechanism depending on the scenario. Of course, this requires all sub-systems to conform to a common service authoring paradigm such as M13.

Web Services are great for exchanging small targeted data between disparate systems. It may be the wrong choice when you have full control over systems on either end of the wire. In those cases, consider more efficient alternatives.