History Service
                      ===============

The HistorySvc collates information about the source and properties of
the job, services, algorithms, algtools, and data objects. Five
differnt objects are recorded by the HistorySvc, as listed below. They
all inherit from the HistoryObj base class.


Objects:
   HistoryObj
      <- JobHistory
      <- ServiceHistory
      <- AlgorithmHistory
      <- AlgToolHistory
      <- DataHistory

JobHistory
----------
 1 per job

  - release version
  - osname
  - hostname
  - os version
  - machine name
  - run directory
  - cmt config
  - start time

ServiceHistory
--------------
  1 per service instantiation

  - link to IService
  - link to JobHistory
  - properties of service

AlgorithmHistory
----------------
  1 per algorithm instantiation

  - alg type
  - alg version
  - alg name
  - properties
  - list<AlgorithmHistory> of all sub algorithms
  - link to Algorithm
  - link to JobHistory

AlgToolHistory
--------------
  1 per algtool instantiation

  - alg tool type
  - alg tool version
  - alg tool name
  - properties
  - link to AlgTool
  - link to JobHistory

DataHistory
-----------
  1 per data object in store

  - storeName
  - dataKey
  - dataClassID
  - link to AlgorithmHistory of alg that created it



Navigating the HistorySvc
-------------------------

Get the history service the normal way with the serviceLocator.

From the service, the following can be accessed:

 Job:
  -> get jobHistory
  -> get all properties of job

 Service:
  -> get SeriviceHistory of a given IService
  -> get all ServiceHistory objs
  -> get properties of a given IService

same for Algorithms, AlgTools

 Data:
  -> get DataHistory obj given (clid,key,store)


Each history object contains links back to the object that it references,
eg an AlgorithmHistory obj will contain a pointer to the Algorithm,
as well as links to a higher level history object. That means that
a DataHistory obj will link back to the AlgorithmHistory obj of the
Algorithm where it was created, and the AlgorithmHistory obj will link
back to the JobHistory of the current job.

The HistorySvc uses the AlgContextSvc to determine which algorithm
is currently being executed, and is thus dependent on the info that
this svc returns. Since AlgTools are NOT instrumented by the
AlgContextSvc, any DataHistory obj that is created by an AlgTool
will report its parent Algorithm as the Algorithm that called
the AlgTool, and not the AlgTool itself. Similarly, if a DataHistory
obj is created from outside an Algorithm, then no AlgHistory obj
will be linked to it.