Siemens V 4.0 manual Job receiver, Join, Lazy evaluation, Local transaction, Navigating access

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Glossary

job receiver

see →server

join

We talk about a join when two or more database tables (i.e. persistent classes) are linked for a database query.

lazy evaluation

Lazy evaluation is when an expression can only ever be evaluated to the extent that is required, as dictated by its use.

In connection with Persistency Service, the procedures used to access persistent objects follow a lazy evaluation strategy. When an object is accessed, the directly deref- erenced object is loaded, rather than the transitive shell of all the references subobjects.

local transaction

A transaction which is restricted to one process is called a local transaction. A →distributed transaction includes all the local transactions.

navigating access

In object-oriented database systems, an object is generally accessed directly using a reference. If this is done on a number of levels, it is called navigating access.

notification

In a hierarchical client/server architecture, only one client can instruct one server. However, in some cases, e.g. for alarms, the reverse information flow is required. In these cases, the server sends a notification to the client. Technically, this is done using an →asynchronous call.

Even the results of →asynchronous calls and →time requests can be presented to the client in the form of a notification. This must be modeled technically.

object-oriented transaction

The transaction principle in GINA is object-oriented. This means that, in contrast to the conventional transaction concept, both the →persistency of objects and communication between objects in the form of calls using the T-ORB undergo transaction monitoring.

Persistency Service

The Persistency Service provides the user programs with an object-oriented view of the related database system.

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