Introduction to Pathmaker

Tandem Databases and TMF
Introduction to Pathmaker and Pathway
1–40 067867 Tandem Computers Incorporated
Database Creation
As stated earlier, a production database is normally created and controlled by a
specially authorized individual in a business, such as a database administrator.
For testing purposes, the Pathmaker product provides a utility program named
PMPROJECT that can assist in creating Enscribe files. The NonStop SQL product
must be used to create a test SQL database.
Before creating a database, consult the applicable Tandem reference manual for further
details.
Overview of TMF The Tandem Transaction Monitoring Facility (TMF) product is a part of the
Encompass data management system. The TMF product simplifies the following
tasks:
Maintaining database consistency
Protecting data from damage caused by system failures
TMF and Database Consistency
One of the steps that must be performed during database design is the establishment
of certain criteria for the relationships between data.
For example, an account balance must always equal its credits minus its debits. When
the data satisfies this criterion, it is considered consistent.
The TMF product helps maintain consistency by ensuring that concurrent transactions
do not interfere with each other. The TMF product also ensures that any changes to
the database resulting from a transaction become permanent only after the entire
transaction is complete.
Remember, a transaction is a multistep operation that changes the database. While
these changes transform the database from one consistent state to a new consistent
state, they can make it inconsistent at points during the transformation.
For example, consider a banking transaction that transfers money from a savings
account to a checking account. If a system failure occurs after the withdrawal from the
savings account but before the deposit to the checking account, the database will be
inconsistent.
To maintain consistency, the TMF product works with an application to ensure that
one of the following is true:
All of the changes a transaction attempts to execute are permanent.
None of the changes is permanent.
In either case, the effect on the database is that consistency is preserved; that is, the
database does not reflect any partial transactions.