Inline Vs. External Policy Attachment SCA Policy Framework

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Inline Vs. External Policy AttachmentSCA Policy
Framework

• Sanjay Patil
• Anish Karmarkar

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Inline Vs. External Policy Attachment
Comparison Criteria Inline Policy Attachment (IPA) External Policy Attachment (EPA)
Separation of roles Developer (creates composite) Deployer (attaches policy sets) Mixes the two roles. Simpler model when SCDL documents are to be manually edited for attaching policy sets Maintains separation of the roles. Composite developer does not have to deal with policy sets. Enables independent management of the policy attachment data (separate from that of SCDL)
Domain-wide policy attachment Not supported Easier to describe domain-wide policy attachment rules
Fine grained policy attachment (per message/operation) Complicates the SCDL Syntax (by duplicating the relevant message/ operation constructs in the SCDL for the purposes of inline policy attachment) Expressions can be formulated for externally attaching policy sets at the message/operation level without requiring any changes to the SCDL metamodel
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EPA is sufficient, prevalent and simpler

• EPA supports all the use cases addressed by IPA
  and more
• Usage of EPA seems to be more prevalent
• Supporting both the mechanisms (EPA and IPA)
  makes the specs complex
• Definition of each mechanism
• Processing rules when EPA and IPA are used
  together

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Other Considerations

• What does it mean to disallow IPA but still allow
  component implementation code to specify defaults
  for policy sets?
• How to handle the scenario where a composite
  developer wants to experiment with attaching
  different policy sets to a SCDL without involving
  the external policy attachment mechanism?

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Proposal

• Option I Support only EPA, remove support for
  IPA, and disallow component implementation code
  to specify policy defaults
• Cleaner architecture
• Simpler specifications and conformance rules
• Minimal/no loss of functionality
• Option II IPA as an optional feature, not to be
  used together with EPA (Note an attribute on
  composite element indicates whether IPA or EPA is
  to be used, with EPA as the default)
• Allows use of IPA while reducing complexity (no
  need to define overriding rules, etc)

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Bindings

• Arguments for the Inline Vs. External Policy
  Attachment discussion also apply for bindings
  attachment
• Treatment of bindings attachment can be based
  upon the resolution for Policy Attachment