Barriers to Sharing Services
Effectively sharing services on a large scale isn't without its challenges and requires a suitable infrastructure to be fully realized. The following environmental characteristics need to be addressed to share services across an SOA effectively.

Platform Diversity
Services are typically created according to the constructs of their native technology environment. This leads to environment-specific technical biases that negatively impact both communication and sharing with other services that are developed using different technology stacks. Given a distributed set of services, it's likely that there will also be differences in the underlying infrastructure, such as communication protocols, technology platforms, and standards, which will impede sharing if not mediated. As such, a vendor/technology-neutral approach is required to span the heterogeneous technology environments.

Geographic Dispersion
If knowledge of a service's physical location is an enabling factor in communicating between services, changes to the service's location or taking a service off-line for maintenance purposes will restrict its ability to communicate and be shared. Without service virtualization, load balancing and failover are impossible. The physical location of a service should be transparent to consumers of that service.

Policy Inconsistency
Infrastructure-related policies can negatively impact service sharing if they're "hard wired" to individual services in an SOA. If this occurs, differences in policies can prevent multiple consumers from sharing a service. For example, one potential consumer of a service may have stringent security requirements, a rigorous Service Level Agreement (SLA), and strict message reliability requirements, while another potential consumer may have minimal security requirements, a low SLA (if at all), and lack message reliability requirements altogether (Table 1).

Without separating infrastructure policy from the physical service, these incompatibilities can prevent sharing this service.

To enable mass consumption of services through service sharing, the functioning of the individual services has to be separated from the underlying infrastructure that enables communication between services. According to Gartner, "SOA is about designing systems as autonomous shared services that are 'black boxes.' The interaction between these black boxes is precisely described through an agreement, which can also be viewed as a 'contract' between services. Thus, organizations have greater capability to modify, extend, or improve individual services independently in cases where there is no change to the underlying contract."

Amplifying Service Consumption
If sharing of services is both an organizational and IT goal, there has to be an environment that facilitates seamless and reliable communication between services but masks the underlying technical complexity of service interaction and communication. The same networking principles that have been applied to distributed technologies for decades - computer networking, storage area networks, and phone networks - can be applied to SOAs to achieve maximum levels of service sharing. Networks allow computers, phones, storage systems, or services, and hence their users, to be linked together for connectivity and sharing in distributed systems.

Amplification of service sharing and consumption can be achieved by including the following functionality in your SOA:

• Creating a network of services that can scale as business needs require
• Building business-driven policy into the network so that IT can dynamically serve the changing needs of the organization
• Mediate between technology incompatibilities that exist in heterogeneous environments to decouple the underlying technical complexity from the operation of the service-oriented solution

By providing this level and breadth of functionality, SOAs can maximize the number of potential consumers that access a service, and align IT with changing business needs.

Introducing Services Networking
A services network consists of services, service consumers, and software intermediaries that mediate the technical incompatibilities that would otherwise limit communication. This is done by separating, or decoupling, the policies that govern the technology infrastructure of an SOA from the business logic found in its services. The services network can then focus on issues related to delivering seamless service communication separate and apart from managing the business function of the services.

A services network assumes heterogeneity in and across IT environments, and mediates between disparate protocols, standards, and message formats. By enabling seamless communication, these mediation capabilities encourage the consumption of business services, which leads to high degrees of service sharing. For instance, let's say a company has an organization-wide approvals process that it has encapsulated as a software service. Assuming that the services network mediates the technology-related issues in the SOA , widespread sharing of the approvals service can occur. Furthermore, while still sharing the service, a legal approval can be treated differently than a purchase order approval according to their respective SLA policies. The base approvals process is used across the organization, enabling consistency, and specific organization needs are also addressed. This focus on global service interoperability delivers an environment that is tolerant of change and inclusive of past, current, and future technology infrastructure.

The mediation capabilities enabled through the use of services networks deliver:

• A vendor/technology-neutral approach that gives IT the freedom to choose the best approach for each project - a choice of platform, messaging provider, security framework, etc.
• Preservation of investment for existing IT assets and technologies
• Future-readiness that insulates SOAs from future technology enhancements and business changes

By mitigating communication issues that exist between services in the network, optimal levels of service sharing can be achieved.

Conclusion
By adopting a SOA-based approach that encourages the sharing of services, such as services networking, organizations can successfully implement IT practices and strategies that enable business agility and deliver successful results. Given its inclusive nature and tolerance of diversity, a services networking approach is the best way to build a successful SOA-based solution.