Herbjorn Wilhelmsen

One of the fundamental goals when designing service-oriented solutions is to attain a reduced degree of coupling between services, thereby increasing the freedom and flexibility with which services can be individually evolved. Achieving the right level of coupling "looseness" is most often considered a design issue that revolves around the service contract and the consumer programs that form dependencies upon it. However, for the service architect there are opportunities to establish intermediate layers of abstraction within the service implementation that further foster reduced levels of coupling between its internal moving parts so as to accommodate the evolution and governance of the service itself. These intermediate abstraction layers are created by the application of Service Façade, a design pattern focused on intra-service design. When designing a service, th... (more)

SOA Pattern of the Week (#5): Service Decomposition

A service inventory is a living body of services that individually will need the freedom to evolve independently over time. What we learned when documenting the SOA design pattern catalog is that there are patterns that emerged not only at design-time but also during this post-implementation evolutionary stage in a service's lifecycle. There is one common scenario that repeatedly surfaced in many projects: When we model and design services during early stages of SOA adoption we are constrained by current infrastructure and technology. These constraints require that we limit the s... (more)

SOA Pattern of the Week (#4): Service Normalization

Like data normalization, the Service Normalization pattern is intent on reducing redundancy and waste in order to avoid the governance burden associated with having to maintain and synchronize similar or duplicate bodies of service logic." You can see it introduces the Pattern on our publisher page. When designing data architectures, you can easily end up with different databases or even different database tables containing the same or similar data. This has been the root of many well documented data maintenance and quality issues that helped establish data normalization as widel... (more)

The Case for Single-Purpose Services

Introduction Services are useful, but they come with a price tag. The cost of developing a service is higher than the cost of developing a traditional (non-service-oriented) application, primarily due to the extra work and infrastructure required. Another common concern when creating and consuming services is the possibility of a performance hit. Together these issues hint that even if you've decided to wholeheartedly adopt SOA, you may not want or need to move all your functionality into services. This is where the application Service Encapsulation becomes a focal point as we ne... (more)

SOA Pattern of the Week (#2): Non-Agnostic Context

Should a service only be considered a service if it's reusable? The answer to this question, as asserted by this pattern, is a firm "no." While agnostic services (services providing multi-purpose logic with reuse potential, as per the Agnostic Context pattern), receive the most attention during service modeling and design phases, it can often be short-sighted to focus only on agnostic service logic. Non-agnostic logic represents any type of functionality that is unique to a given business process or task. In other words, non-agnostic logic is single-purpose in nature and therefo... (more)