James

							  SLAng specification compiler
         and checker
• Spin-off work from SLAng specification
• Tools demos
  – Specification compiler
     • Generates checker from SLAng language specification
  – SLAng checker
     • Partly an application
     • Partly a component
         – Can be part of an application server
         – Can be part of an external monitor
         – Can (possibly) be re-implemented using EJBs.
         Where does SLA checker
            component go?
                     Measurement service
                            Here!



  Provider                                   Service consumer
                           Internet                Here!
      Here!


In short: Anywhere that a decision has to be made about an SLA.
                           But!
• Monitoring using a third party has a DIFFERENT
  SEMANTICS to monitoring at ASP or client side.
• Client was saying:
   – I want good service
• Client is now saying:
   – I want the third party to get good service, and I believe
     that if it does, then I too will get good service.
• SLAng will need modification if we apply the
  latter semantic.
• Trust issues and implementation are different in
  each case.
       SLA checker application
• Component features
   – Load/save SLAs
   – API for monitoring data
   – API for performing checks, retrieving
     violations/guidance values
   – Database storage (SLAs/monitoring data)
   – OCL checker
• Application features/.
   – View SLAs
   – View events
   – Check SLAs
              Specification compiler
•    Idea:
    1.   Understanding of SLA language based on specification
    2.   Parties will make agreements based on their understanding of
         the specification.
    3.   SLA checker must:
         1.   Report all violations implied by the specification (no false
              positives)
         2.   Not report violations not implied by the specification (no false
              negatives)
    4.   Specification is in machine readable form.
    5.   Therefore: Compile SLA check from specification.
    6.   If we trust our compilation process, then we trust our checker.
                   What is generated?
Specification:                   Implementation:
         SLAng       Compiler:   SLAng database schema
         syntax                  SLAng API/Java objects
         model                   SLAng XML reader/writer
                                 User interface classes

      SLAng                      Event database schema
      semantic                   Event API/Java objects
      model
                                 User interface classes


     SLAng                       Java checks
     semantic                    Violations API
     constraints
          Compiler architecture


XMI Reader    Intermediate   Context     Code
(DOM based)   document       objects     generation
              model                      Procedure
              (DOM for                   (execute
              XMI)                       velocity
                                         engine)
                             Velocity
                             templates