HP 3000 Manuals

HP IMAGE/SQL Administration Guide

How IMAGE/SQL Works 

IMAGE/SQL users can select data in mapped tables in the same way that
data in ALLBASE/SQL tables is selected.

To understand how this is accomplished, you need to know:

   *   What files are used by IMAGE/SQL
   *   How IMAGE/SQL files are used
   *   What takes place during the attach/detach process
   *   How IMAGE/SQL maps TurboIMAGE/XL security
   *   How IMAGE/SQL maps TurboIMAGE/XL data types
   *   What takes place at run time

IMAGE/SQL Files 

IMAGE/SQL creates two files:  ATCINFO in the same group and account as
the DBEnvironment and DBNameTC in the same group and account as the
TurboIMAGE/XL database.  This is shown in Figure 3-1 .


          Figure 3-1.  Files Created by IMAGE/SQL 

These files contain information about the relationships between all
attached TurboIMAGE/XL databases and their DBEnvironments.  Specifically:

ATCINFO       is a permanent privileged file in the same group and
              account as the DBEnvironment.  It contains mapping
              information about each TurboIMAGE/XL database attached to
              the DBEnvironment.  One ATCINFO file exists for each
              DBEnvironment.

              It is named ATCINFO unless a file equation has been set
              before the attach.  Its name is placed in the DBECon file
              of the DBEnvironment so that it can be located whenever
              IMAGE/SQL needs to use or update the information in this
              file.

DBNameTC      is a permanent privileged file in the same group and
              account as the TurboIMAGE/XL database.  It contains the
              fully qualified names of the DBEnvironments to which the
              TurboIMAGE/XL database is attached.  This information is
              used to let external utilities such as DBUTIL know that the
              database is attached to one or more DBEnvironments.

What Takes Place During an Attach? 

An attach is the process that establishes the connection between the
TurboIMAGE/XL database and the DBEnvironment.  Figure 3-2  shows a
TurboIMAGE/XL database and DBEnvironment before the TurboIMAGE/XL
database is attached.


          Figure 3-2.  A TurboIMAGE/XL Database and a DBEnvironment Before the Attach 

When the TurboIMAGE/XL database is attached to the DBEnvironment, several
events take place:

   1.  The ATCINFO and DBNameTC files are created.

   2.  Definitions of the TurboIMAGE/XL mapped tables are placed in the
       system catalog of the DBEnvironment.  These entries in the system
       catalog identify the tables as mapped tables.  The naming
       convention for SQL tables is OwnerName.TableName.  By
       default, in mapped tables, IMAGE/SQL specifies the database
       name as the owner name and the data set name as the table
       name.  Thus, the naming convention for mapped tables is
       MappedDatabaseName.MappedDataSetName.  (At attach time, you must
       substitute a different owner name if an already attached database
       has the same name.)

   3.  The TurboIMAGE/XL database creator (DBC) is defined in the ATCINFO
       file as an IMAGE/SQL user.  (For security reasons, all other
       IMAGE/SQL users must be explicitly added by the DBC.)

Figure 3-3 shows an attached database.


          Figure 3-3.  An Attached TurboIMAGE/XL Database 

What Takes Place During a Detach? 

When a database is detached, you can no longer use SQL to access
TurboIMAGE/XL data.  All views based on mapped tables are dropped.  This
includes views created by users, as well as IMAGE/SQL-created views.
Mapped table definitions are removed from the system catalog and all
mapping information about the detached TurboIMAGE/XL database is removed
from the ATCINFO file.

If you are detaching the only TurboIMAGE/XL database attached to the
DBEnvironment, the ATCINFO file is deleted and its name is removed from
the DBECon file.  If you are detaching the TurboIMAGE/XL database from
the only DBEnvironment it is attached to, the DBNameTC file is deleted.

Detach if you plan to restructure the database or if you want to remove
all mapping information about the database from the ATCINFO file.

When the database is detached, all customized mapping information
(alternative data types and added IMAGE/SQL users) is lost and must be
remapped when the database is reattached.  IMAGE/SQL utility command
files are useful for this purpose (refer to Tasks 12 and 13 in Chapter
2).  but to protect database security, be sure command files that contain
passwords and other sensitive information are carefully controlled.  (A
message notifies you when IMAGE/SQL commands containing maintenance words
or passwords have been logged.)

MPE/iX 5.0 Documentation