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 |
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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 |
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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 |
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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
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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.
