HP 3000 Manuals

Getting Started with HP IMAGE/SQL

Methods of Accessing Databases 

TurboIMAGE/XL and IMAGE/SQL both offer a variety of tools for accessing
databases and both provide techniques for concurrency control, which
regulates access by more than one user at a time.

Interactive Access 

TurboIMAGE/XL interactive access is through Query/3000, which lets you
find database entries and report on them using the Query command
language.  In IMAGE/SQL, the interactive interface is known as ISQL,
which uses Structured Query Language (SQL) to access the database and
display query results.

Programmatic Access 

A major difference between TurboIMAGE/XL and IMAGE/SQL is in the
programmatic interface.  TurboIMAGE/XL provides a set of intrinsics that
you use in application programs to open databases, obtain locks, retrieve
data, unlock data items and data sets, and close a database.

IMAGE/SQL uses embedded SQL programming.  You insert standard SQL
statements in an application program, then you preprocess the program to
convert the SQL statements into valid procedure calls in the language you
are using.  The converted code is compiled and linked with a library of
IMAGE/SQL routines.  You can prototype and test your queries in ISQL
before using them in an application, thus saving development time.
Embedded SQL also includes a set of dynamic statements that let your end
users perform queries, inserts, updates, and deletes through your
applications.

Locking Mechanisms 

In TurboIMAGE/XL, you use the DBLOCK intrinsic in certain access modes to
provide locking at the database level, the data set level, or the data
item level.  Locking must be explicitly requested by the user; it is
required for concurrent updates.  You can request locks conditionally in
TurboIMAGE/XL, which means that the call returns if the lock request
fails.

In IMAGE/SQL, locking is provided when:

   *   it is implicitly specified when the data is accessed (such as when
       inserting, deleting, or updating.)  The whole data set is locked
       until the end of the transaction.  For example,

              BEGIN WORK

              SELECT * FROM Turbo.Dataset

              DELETE FROM Turbo.Dataset      <-----  LOCK begins
                  WHERE Mynumber=25

              SELECT * FROM Turbo.Dataset

              COMMIT WORK                    <-----  UNLOCK occurs

   *   it is explicitly specified by the LOCK TABLE statement.

Locking is unconditional and applies at the table level; row and page
level locking is not supported.  Refer to the ALLBASE/SQL Reference 
Manual for more details.

MPE/iX 5.0 Documentation