api20/src/java/javax/jdo/package.html - db-jdo - Git at Google

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 <html>
 <head>
 <title>JDO package</title>
 <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
 </head>

 <body bgcolor="#FFFFFF">
 This package contains the JDO specification interfaces and classes.
 <P>There are two major objectives of the JDO architecture:
 first, to provide application programmers a transparent,
 Java-centric view of persistent information, including enterprise data
 and locally stored data; and second, to enable pluggable implementations
 of data stores into
 application servers.  Data stored in data stores is presented as
 instances of persistence-capable classes.
 <P>JDO defines interfaces and classes to be used by application programmers
 when using classes whose instances are to be stored in persistent storage
 (persistence-capable classes), and specifies the contracts between
 suppliers of persistence-capable classes and the
 runtime environment (which is part of the JDO implementation).
 <P>The JDO architecture defines a standard set of contracts between an
 application programmer and an JDO vendor. These contracts focus on the
 view of the Java instances of persistence capable classes.
 <P>The JDO PersistenceManagerFactory is the boostrap class for a JDO
 application.  The application gets an instance of the
 PersistenceManagerFactory by construction or via JDNI lookup.
 <P>The application acquires an instance of the JDO PersistenceManager by
 calling the getPersistenceManager method on an instance of JDO
 PersistenceManagerFactory.
 <P>The JDO PersistenceManager is the primary interface for JDO-aware
 application components:
 <ul>
 <li>it gives access to the current Transaction interface;
 <li>it is the factory for the Query interface;
 <li>it contains methods for managing the life cycle of persistent instances.
 </ul>
 <P>A JDO PersistenceManager instance supports any number of JDO instances
 at a time. It is responsible for managing the identity of its
 associated JDO instances. A JDO instance is associated with either
 zero or one JDO PersistenceManager. It will be zero if and only if the
 JDO instance is transient nontransactional. As soon as the instance is made persistent
 or transactional, it will be associated with exactly one JDO PersistenceManager.
 <P>A JDO PersistenceManager instance supports one transaction at a time,
 and uses one connection to the underlying data source at a time. The JDO
 PersistenceManager instance might use multiple transactions serially,
 and might use multiple connections serially.
 <P>Normally, cache management is automatic and transparent. When instances
 are queried, navigated to, or modified, instantiation of instances and
 their fields and garbage collection of unreferenced instances occurs
 without any explicit control. When the transaction in which persistent
 instances are created, deleted, or modified commits, eviction is
 automatically done by the transaction completion mechanisms.
 <P>Operations on persistent JDO instances at the user's choice might be
 performed in the context of a transaction. That is, the view of data
 in the data store is transactionally consistent, according to the
 standard definition of ACID transactions.
 <P>The Transaction interface is used to mark the beginning and end of a
 application-defined unit of work.  The PersistenceManager allows the
 application to get the instance that manages these transactional
 boundaries via the currentTransaction method.
 <P>The persistent manager instance is a factory for query instances,
 and queries are executed in the context of the persistent manager instance.
 The actual query execution might be performed by the JDO PersistenceManager
 or might be delegated by the JDO PersistenceManager to its data store.
 The actual query executed thus might be implemented in a very different
 language from Java, and might be optimized to take advantage of particular
 query language implementations.
 <P>Extents are collections of data store objects managed by the data store,
 not by explicit user operations on collections. Extent capability is a
 boolean property of classes that are persistence capable. If an instance
 of a class that has a managed extent is made persistent via reachability,
 the instance is put into the extent implicitly.
 </body>
 </html>
	<!--
	Copyright 2005 The Apache Software Foundation.

	Licensed under the Apache License, Version 2.0 (the "License");
	you may not use this file except in compliance with the License.
	You may obtain a copy of the License at

	http://www.apache.org/licenses/LICENSE-2.0

	Unless required by applicable law or agreed to in writing, software
	distributed under the License is distributed on an "AS IS" BASIS,
	WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	See the License for the specific language governing permissions and
	limitations under the License.
	-->

	<html>
	<head>
	<title>JDO package</title>
	<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
	</head>

	<body bgcolor="#FFFFFF">
	This package contains the JDO specification interfaces and classes.
	<P>There are two major objectives of the JDO architecture:
	first, to provide application programmers a transparent,
	Java-centric view of persistent information, including enterprise data
	and locally stored data; and second, to enable pluggable implementations
	of data stores into
	application servers. Data stored in data stores is presented as
	instances of persistence-capable classes.
	<P>JDO defines interfaces and classes to be used by application programmers
	when using classes whose instances are to be stored in persistent storage
	(persistence-capable classes), and specifies the contracts between
	suppliers of persistence-capable classes and the
	runtime environment (which is part of the JDO implementation).
	<P>The JDO architecture defines a standard set of contracts between an
	application programmer and an JDO vendor. These contracts focus on the
	view of the Java instances of persistence capable classes.
	<P>The JDO PersistenceManagerFactory is the boostrap class for a JDO
	application. The application gets an instance of the
	PersistenceManagerFactory by construction or via JDNI lookup.
	<P>The application acquires an instance of the JDO PersistenceManager by
	calling the getPersistenceManager method on an instance of JDO
	PersistenceManagerFactory.
	<P>The JDO PersistenceManager is the primary interface for JDO-aware
	application components:
	<ul>
	<li>it gives access to the current Transaction interface;
	<li>it is the factory for the Query interface;
	<li>it contains methods for managing the life cycle of persistent instances.
	</ul>
	<P>A JDO PersistenceManager instance supports any number of JDO instances
	at a time. It is responsible for managing the identity of its
	associated JDO instances. A JDO instance is associated with either
	zero or one JDO PersistenceManager. It will be zero if and only if the
	JDO instance is transient nontransactional. As soon as the instance is made persistent
	or transactional, it will be associated with exactly one JDO PersistenceManager.
	<P>A JDO PersistenceManager instance supports one transaction at a time,
	and uses one connection to the underlying data source at a time. The JDO
	PersistenceManager instance might use multiple transactions serially,
	and might use multiple connections serially.
	<P>Normally, cache management is automatic and transparent. When instances
	are queried, navigated to, or modified, instantiation of instances and
	their fields and garbage collection of unreferenced instances occurs
	without any explicit control. When the transaction in which persistent
	instances are created, deleted, or modified commits, eviction is
	automatically done by the transaction completion mechanisms.
	<P>Operations on persistent JDO instances at the user's choice might be
	performed in the context of a transaction. That is, the view of data
	in the data store is transactionally consistent, according to the
	standard definition of ACID transactions.
	<P>The Transaction interface is used to mark the beginning and end of a
	application-defined unit of work. The PersistenceManager allows the
	application to get the instance that manages these transactional
	boundaries via the currentTransaction method.
	<P>The persistent manager instance is a factory for query instances,
	and queries are executed in the context of the persistent manager instance.
	The actual query execution might be performed by the JDO PersistenceManager
	or might be delegated by the JDO PersistenceManager to its data store.
	The actual query executed thus might be implemented in a very different
	language from Java, and might be optimized to take advantage of particular
	query language implementations.
	<P>Extents are collections of data store objects managed by the data store,
	not by explicit user operations on collections. Extent capability is a
	boolean property of classes that are persistence capable. If an instance
	of a class that has a managed extent is made persistent via reachability,
	the instance is put into the extent implicitly.
	</body>
	</html>