157. The following guiding principles derived from the WS-I Basic Profile[5] are proposed to drive the development of a consolidated SIP/SDS Profile:
158. The Profile SHOULD provide further clarifications to open and NATO standards and specifications. This cannot guarantee complete interoperability, but will address the most common interoperability problems experienced to date.
The Profile SHOULD NOT repeat referenced specifications but make them more precise.
The Profile SHOULD make strong requirements (e.g., MUST, MUST NOT) wherever feasible; if there are legitimate cases where such a requirement cannot be met, conditional requirements (e.g., SHOULD, SHOULD NOT) are used. Optional and conditional requirements introduce ambiguity and mismatches between implementations. The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in [IETF RFC 2119].
The Profile SHOULD make statements that are testable wherever possible. Preferably, testing is achieved in a non-intrusive manner (e.g., by examining artefacts "on the wire").
The Profile MUST provide information on externally visible interfaces, behaviour and protocols, but it SHOULD NOT provide internal implementation details. It MAY also state non-functional requirements to the service (e.g., notification broker must store subscription information persistently in order to survive system shutdown).
The Profile MUST clearly indicate any deviations and extensions from the underlying referenced specifications. It is RECOMMENDED that any extensions make use of available extensibility points in the underlying specification. The extensions MUST be made recommended or optional in order to not break interoperability with standard-compliant products (e.g. COTS) that will not be able to support NATO specific extensions. Extensions SHOULD be kept to the minimum.
When amplifying the requirements of referenced specifications, the Profile MAY restrict them (e.g., change a MAY to a MUST), but not relax them (e.g., change a MUST to a MAY).
If a referenced specification allows multiple mechanisms to be used interchangeably, the Profile SHOULD select those that best fulfil NATO requirements, are well-understood, widely implemented and useful. Extraneous or underspecified mechanisms and extensions introduce complexity and therefore reduce interoperability.
Backwards compatibility with deployed services is not a goal of the SIP, but due consideration is given to it.
Although there are potentially a number of inconsistencies and design flaws in the referenced specifications, the SIP MUST only address those that affect interoperability.