Network Router User Manual

GINA V4.0 System Administrator Guide – September 2000 207
Glossary
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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.