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Management of Instance Lists in an Object Oriented System

IP.com Disclosure Number: IPCOM000114162D
Original Publication Date: 1994-Nov-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 98K

Publishing Venue

IBM

Related People

Chen, C: AUTHOR [+2]

Abstract

A uniform method of managing instance lists to provide object information at run time is described. In an object oriented system, most objects exist within specific 'supertype/subtype' hierarchies. Subtype objects inherit attributes from their supertype objects. A supertype object serves as an abstract representation for all of its subtypes. There may be zero, one, or many 'instances' of an 'object' existing in the system simultaneously. To manage the instances of objects, an instance list needs to be maintained for each object. Depending on the object, instance lists may also be desired at the supertype object level as well.

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Management of Instance Lists in an Object Oriented System

      A uniform method of managing instance lists to provide object
information at run time is described.  In an object oriented system,
most objects exist within specific 'supertype/subtype' hierarchies.
Subtype objects inherit attributes from their supertype objects.  A
supertype object serves as an abstract representation for all of its
subtypes.  There may be zero, one, or many 'instances' of an 'object'
existing in the system simultaneously.  To manage the instances of
objects, an instance list needs to be maintained for each object.
Depending on the object, instance lists may also be desired at the
supertype object level as well.

      A description of a working implementation with the option of
supporting instance lists for supertype objects only where they are
needed is presented.  This implementation relies on a process that
extracts necessary information from the object models used during
analysis.

      With a uniform method of managing instance lists in an object
oriented system, the following information can be acquired for any
object much easier during system execution:
  o  Total number of instances
  o  The first instance that satisfies given criteria
  o  The last instance, that satisfies given criteria
  o  The first instance
  o  The last instance

      The instances of a supertype object are the collection of all
instances of its subtype objects.  Creating a subtype instance causes
the newly created instance to be added to its own and to its
supertype's instance lists.  If an instance list is maintained for
each object in the system, each instance creation/deletion may cause
several different instance lists to be updated as well.  Managing
additional instance lists requires more system memory and adds
performance overhead.  A key to maintaining a balance between memory
utilization and system performance is to only support instance lists
on the objects that require it to function.

      As a design point, an instance list is automatically maintained
for each true subtype or stand-alone object in the system.  With the
instance lists of all true subtype and stand-alone objects, each
instance created can be located in the system during execution.  In
order to extend the instance support to supertype objects, each
developer must indicate the requirement for a supertype instance list
in models used for analysis.  This information is extracted and used
to control the ma...