The MIB module allows a management application to
select a set of MIB object instances whose values need 
to be collected on a periodic basis. The term 'data' in 
the context of this MIB is used to generically refer to 
the values of the selected set of object instances. 

Once the required setup is done, the MIB implementation 
carries out the following periodic tasks:
  - collects the required object values into local
    file-like entities called VFiles (virtual files).
  - transfers the VFiles to specified locations.
  - carries out VFile management operations.

Some of the key features of this MIB are:
  a) Allows grouping of MIB objects into groups called 
     data groups. The constraint is that the MIB objects 
     grouped into a data group, need to have the same 
     semantic MIB index. So it is possible to group MIB 
     objects belonging to different MIB tables into a 
     single data group as long as the above constraint is 
     met.
     For e.g. it is possible to group ifInOctets from 
     ifTable, ifHCInOctets from ifXTable, 
     dot3StatsExcessiveCollisions from dot3StatsTable 
     into a single data group.

  b) Allows the application to specify a set of instances 
     (of the MIB objects in a data group) whose values 
     need to be collected. 

  c) The required data can be collected for each such 
     data group on a periodic basis into a virtual file
     (VFile). A VFile is an abstraction of a file. 

  d) The format of the contents of the VFile, can be 
     specified by the application. 

  e) An application can also specify a collection period. 
     A collection period is an interval of time during 
     which data is collected into a VFile. After the 
     collection period ends, the VFile is frozen, and a 
     new VFile is created for storing data. The frozen 
     VFile is then transferred to a specified destination. 
     An application can choose to retain such frozen 
     VFiles on the device for a certain period of time, 
     called the retention period. 

         Data Collection MIB vs Bulkfile MIB
         ***********************************
   The data collection MIB can pretty much do what the
   CISCO-BULK-FILE-MIB (Bulkfile MIB) can do. The 'manual' 
   mode of the Data collection MIB is similar to the way 
   in which the Bulkfile MIB operates.

   However the data collection MIB is mainly targetted 
   for medium to high-end platforms which have sufficient
   local storage (volatile or permanent) to store VFiles.
   Locally storing VFiles, helps minimize loss of data 
   during temporary network outages. If the local store 
   is permament, then the collected data is also available 
   across agent restarts.  

   The data collection MIB has more powerful data 
   selection features than the Bulkfile MIB. It allows 
   grouping of MIB objects from different tables into 
   data groups. It also incorporates a more flexible 
   instance selection mechanism, where the application 
   is not restricted to fetching an entire MIB table. 

                Definitions:
                ************
    Base objects: 
    *************
    MIB objects whose values an application needs to 
    collect.

    Data group:
    ***********
    A group of base objects. Can be of 2 types: 'object' 
    and 'table'. An 'object' type data group can consist 
    of only one fully instantiated base object. A 'table'
    type data group can consist of more than one base
    objects, each a columnar object in a conceptual
    table. In addition a 'table' type data group can
    specify the instances of the base objects whose 
    values need to be collected. In the context of this 
    MIB, collecting data for a data group means fetching 
    the values of the associated base object instances 
    and storing them into VFiles.

    Virtual File (VFile):
    *********************
    A VFile is a file like entity used to collect data. 
    An agent might choose to implement a VFile as a 
    simple in-memory buffer, or it might choose to
    use a file in it's filesystem. An application does
    not really need to know the location of a VFile 
    - the MIB provides mechanisms to transfer the 
    VFile to application specified locations. However 
    if the implementation supports it, the application 
    can specify the location of the VFiles.

    Current VFile:
    **************
    The VFile into which data is currently being 
     collected.

    Frozen VFile:
    *************
    A VFile which is no longer used for collecting 
    data. Only frozen VFiles can be transferred to 
    specified destinations.

    Collection interval:
    ********************
    A collection interval is associated with a VFile.
    It is the interval of time over which a VFile 
    is used to collect data. 
    This interval of time can be specified by the 
    application. However there are conditions under 
    which a collection interval can be shorter than 
    the specified time. For e.g. a collection 
    interval is prematurely terminated when the 
    maximum size of a VFile is exceeded, or when 
    there is an error condition.

    Polling period:
    ***************
    A polling period is associated with a data 
    group. It determines the frequency at which 
    the base objects of a data group should
    be fetched and stored into a VFile.

    Data collection operations:
    **************************
    A generic term used to refer to operations 
    that are carried out while collecting data. 
    These include:
       - Periodically creating new VFiles for 
         collecting data.
       - Transferring frozen VFiles either 
         automatically or on demand.
       - Fetching base object values and storing 
         them into current VFiles, either periodically 
         or on demand.
       - Deleting frozen VFiles, either periodically 
         or on demand.