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White Paper:
InterPlex
Enterprise Gateway
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Login
And Initialization Procedures
The
gateway will perform login and initialization functions the first time a
user or application requests data from the DMS database via InterPlex SQL.
It is important to note that the DataServer’s user-id and
password of the application will be passed through for verification in the
InterPlex SQL product. Therefore,
matching user-ids/passwords should be maintained within InterPlex SQL via
the administration functions. Once the user-id has been authorized, the user catalog is retrieved
from the mainframe. This user
catalog is maintained on the mainframe and is held in memory on the
computer where the gateway is executing until the user logs off.
It contains all the accessible tables, public and private, for the user
as well as the identity of the generated mainframe procedures used for
fast access and updates.
Overview Of ANSI SQL
Transactions
An
ANSI SQL transaction is a logical unit of work that takes a database from
one consistent state to another. It
comprises one or more SQL statements.
According to the ANSI SQL standard, a transaction begins with the
user’s first SQL statement, and ends with an explicit commit or
rollback.
Commit
and/or rollback will terminate the SQL transaction.
A commit of a SQL transaction makes permanent the changes resulting
from all the SQL statements in the transaction.
Rolling back a SQL transaction cancels any changes resulting from
the SQL statements in the transaction.
After a transaction is rolled back, the affected data is in the
state it was before the statements in the ANSI SQL transaction were
executed.
There
are two basic types of transactions, Single-Site or Remote Transaction and
Distributed
Transaction.
A Remote or Single-Site transaction contains SQL statements, which
reference one or more tables, all of which reside at the same node.
A distributed transaction contains SQL statements, which reference
data on two or more distinct nodes of a distributed database.
InterPlex
SQL supports Single-Site or Remote
transaction processing. Two-Phase commit processing only applies to
distributed transactions although a single-site transaction must be able
to perform commit and rollback processing as well as presumed abort.
The Unisys data sources are considered another Database
Node with the presumed abort model in effect by the InterPlex
Enterprise gateway. Presumed
abort means that if a failure occurs during a transaction before the
commit/rollback phase, the transaction is assumed to have failed and a
rollback occurs.
Transparency
Issues
The
InterPlex Enterprise gateway product provides client applications with
SQL-based access to the Unisys DMS database.
InterPlex Enterprise gateway and the DataServer provide a single
consolidated view of an organization’s data and services.
The client’s view is that of a single logical database comprising
a distributed database with multiple independent databases, integrated
with services provided by the DataServers procedures and functions.
These procedures and functions provide a number of benefits such as
encapsulation of business rules and access to Unisys DMS legacy systems.
This
simple client view is necessary to allow many different client
implementations, ranging from PCs to mainframes and different client
interfaces to store and retrieve data.
By supporting this client environment, InterPlex Enterprise gateway
becomes a cooperating server in the DataServer environment.
It
is not enough to provide this coherent view of data for new applications,
but also must provide for the integration of existing data and services
from pre-existing applications and systems.
It must be possible to make changes in the location, number and
function of servers in a complex environment over time as the information
processing needs of the organization change.
It is only through a complete cooperative server environment;
supplied by InterPlex and the DataServer that this can be achieved in the
Unisys ClearPath IX or 2200 mainframe environment.
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UNISYS Integrators