Alfredo,

You wrote:
> I wanted to repeat ALL of Jeff's wonderful essay because it captures the
> essence of IMAGE databases.  IMAGE has built-in redundancy for safety
> (just as airplanes have built-in redundancy for safety).  Pointers in
IMAGE
> are not necessary at all.  Pointers are there just for performance
reasons,
> to avoid serial scans.  You can dynamically add/delete/rebuild pointers
at
> any time (witness these Adager functions: PathAdd, PathDel, PathFix,
>  MastPack, DetPack).

I want to include that Codd & Dates conception of a relational database
includes exactly the features you described (contrary to what Jeff wrote --
if I understand him correctly).

QUESTION:  Does Adager now allow one to rebuild pointers "at any time",
including while the database is open by other users?

IMAGE seems to have been designed so as to allow some relational style
features to be added in the future.    For instance, I would like to have
relational style "Primary Keys" (a.k.a. unique keys) in detail datasets.
Having a relational type primary key also strongly implies support of
concatenated keys.
      While I don't know how hard it would be to add concatenated keys to
IMAGE,  support of a unique key check would be fairly straight forward.
To wit:
    1.  Add a  unique key command to DBSCHEMA.
    2.  Add a unique key flag to the root file.
    3.  Add a new unique key error status code to DBPUT and DBUPDATE.
    4.  Modify DBPUT and DBUPDATE (with CIUPDATE option) to check the
length of the chain on the primary key path before adding or updating;  if
the length is already > 0 then set the new error status and quit.

If I understand the IMAGE internals correctly then the system overhead of
this check would be negligible.   While concatenated keys might well
involve more re-programming for HP's engineers the performance implications
would again be negligible.

When the DBQUIESE and multiple database UNDO (MXUNDO) commands come on line
in the next year or so IMAGE will have two more key relational features to
add to IMAGE/SQL.    The addition of a unique key option for detail
datasets would bring IMAGE very close to Codd's minimal definition of a
relational database.

Not bad for a database released just 2 years after the first public
publication of the earliest relational model!

- Cortlandt