90. Within the heterogeneous NATO environment, experience has shown that different services implement differing standards, or even different profiles of the same standards. This means that the interfaces between the services of the Core Services (CS) need to be tightly defined and controlled. This is the only way to achieve interoperability between diverse systems and system implementations. Recommendations for the use of specific open standards for the individual CES are laid down in the C3B document “CES Standards Recommendations - The SOA Baseline Profile” [SOA Baseline].
91. Experience shows that while open standards are a good starting point, they are often open to different interpretations which lead to interoperability issues. Further profiling is required and this has been independently recognized by NCI Agency (under ACT sponsorship) and Nations.
92. The Service Data Sheet (SDS) (for example [DEU SDS]) and SIP (for example [NC3A RD-3139], NCI Agency) have chosen slightly different approaches. The SIP tries to be implementation agnostic, focusing on interface and contract specification, with no (or minimal, optional and very clearly marked) deviations from the underlying open standard. The SDS is more implementation specific, providing internal implementation details and in some cases extends or modifies the underlying open standard, based on specific National requirements. Previous experience with the former CES WG while working on [SOA Baseline] is that Nations will not accept any implementation details that might constrain National programmes. Therefore, a safer approach seems to focus on the external interfaces and protocol specification.