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EclipseLink/UserGuide/Glossary (ELUG)

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This glossary contains terms and abbreviations that you should be familiar with when using EclipseLink.


A

attribute

A variable of a class or object. In EclipseLink, an attribute describes all instance variables of a class. Every attribute contains a single mapping. Attributes store primitive data such as integers, and simple Java types such as String or Date.


authentication

The means by which a data source validates a user's identity and determines whether or not the user has sufficient privileges to perform a given action.


B

bean class

The implementation of the bean. The bean is accessed from the client using the home and remote interfaces. bean-managed persistence (BMP)

A scheme for persisting entity beans that requires the developer to manually code the methods that perform the persistence.

Compare to container-managed persistence (CMP).


branch class

Has a persistent superclass and also has subclasses. By default, queries performed on the branch class return instances of the branch class and any of its subclasses. However, the branch class can be configured so that queries on it return only instances of itself without instances of its subclasses.

Compare to leaf class.


C

class

A category of objects. Classes allow data and method to be grouped together.


class indicator field

A field in the table of the root class that indicates which subclass should be instantiated


client session broker

A collection of client sessions, one from each server session associated with the session broker.


connection pool

A collection of reusable connections to a single data source.


custom SQL

Refers to any non-EclipseLink-generated SQL used through EclipseLink. This includes hard-coded SQL and stored procedure calls.

D

data definition language (DDL)

The data definition part of the structured query language (SQL). The Workbench can generate DDL creation scripts that can be used to create tables on the desired database.


database session

A database session provides a client application with a single data store connection, for simple, standalone applications in which a single connection services all data store requests for one user.


default mapping

A relational persistence framework term that refers to making the framework automatically generate the object descriptor metadata (including such things as mappings, login data, database platform, locking, and foreign keys). Default mapping is available for EclipseLink projects using EJB 2.0 CMP applications with OC4J.


dependent class path (IBM WebSphere)

Location where nonbean classes are specified. EclipseLink requires that the bean classes be included here since they are referenced by the project.


deployment descriptor

A set of XML files that provide the additional required information to install an EJB within its server. Typically, this incudes security, transaction, relationship, and persistence information.

Compare with EclipseLink descriptors.


descriptors

An EclipseLink object that describes how an object's attributes and relationships are to be represented in relational database table(s). An "EclipseLink descriptor" is not the same as a deployment descriptor, although it plays a similar role.


direct access

By default, EclipseLink accesses public attributes directly when writing the attributes of the object to the database or reading the attributes of the object from the database.

Compare to method access.


direct mapping

There are two basic ways of storing object attributes directly in a table:

  • The information can be stored directly if the attribute type is comparable to a database type.
  • If there is no database primitive type that is logically comparable to the attribute's type, it must be transformed on its way to and from the database

EclipseLink provides five classes of direct mappings.

Compare to relationship mapping.


E

EclipseLink session broker

A mechanism that enables client applications to transparently access multiple databases through a single EclipseLink session.


Enterprise Java Beans (EJB)

EJB are server-side domain objects that fit into a standard component-based architecture for building enterprise applications with Java. They are objects that become distributed, transactional, and secure components. Workbench uses three types of EJB: session beans, entity beans, and message-driven beans.


expressions

The EclipseLink equivalent of an SQL conditional clause. EclipseLink expressions are specified using the Expression and ExpressionBuilder classes.


entity beans

EJB that represent a persistent data object. EclipseLink uses two schemes for persisting entity beans: bean-managed persistence (BMP) and container-managed persistence (CMP).


F

fetch group

A performance enhancement that defines a subset of object attributes to be loaded initially and ensures that all other attributes are loaded on demand.


H

hub

A common connection point for devices in a network.


I

identity map

Used to cache objects for performance and to maintain object identity.

See also object identity.


independent relationship

A relationship in which the source and target are public objects that exist independently; the destruction of one object does not necessarily imply the destruction of the other.

Compare to private relationship.


indirection

The EclipseLink term for lazy loading.

By default, when EclipseLink retrieves a persistent object, it retrieves all of the dependent objects to which it refers. When you configure indirection (also known as lazy loading, lazy reading, and just-in-time reading) for an attribute mapped with a relationship mapping, EclipseLink uses an indirection object as a place holder for the referenced object: EclipseLink defers reading the dependent object until you access that specific attribute. This can result in a significant performance improvement, especially if the application is interested only in the contents of the retrieved object, rather than the objects to which it is related.

EclipseLink supports a variety of types of indirection, including: value holder indirection, transparent indirect container indirection, and proxy indirection.


inheritance

Describes how a child class inherits the characteristics of its parent class. EclipseLink supports multiple approaches to database implementations that preserve the inheritance relationship.


in-memory query

A query that is run against the shared session cache.


instantiate

Create an instance of a Java class.


J

JCA

The Java EE Connector architecture (JCA) adapter is a way to persist Java objects to a nonrelational data source, such as XML.


Java SE

The Java Platform, Standard Edition (Java SE) is the core Java technology platform. It provides software compilers, tools, runtimes, and APIs for writing, deploying, and running applets and applications in Java.


Java EE

The Java Platform, Enterprise Edition (Java EE) is an environment for developing and deploying enterprise applications. Java EE includes a set of services, APIs, and protocols for developing multitiered web-based applications.


Java EE Containers

A Java EE container is a run-time environment for Enterprise Java Beans (EJB) that includes such basic functions as security, life cycle management, transaction management, and deployment services. Java EE containers are usually provided by a Java EE server, such as Oracle Containers for J2EE.


Java Messaging Service (JMS)

The JMS API is a protocol for communication that provides asynchronous communication between components in a distributed computing environment.


Java Naming and Directory Interface (JNDI)

The JDBC specification recommends using a JNDI naming service to acquire a connection to a database. EclipseLink supports acquiring a database connection in this fashion. To take advantage of this feature, construct and configure an instance of org.eclipse.persistence.sessions.JNDIConnector and pass it to the project login object using the setConnector method.


Java Persistence API (JPA)

The Java Persistence API (JPA) provides a POJO persistence model for object-relational mapping in both Java EE and Java SE applications.


Java Transaction API (JTA)

The Java Transaction API (JTA) specifies the interfaces between a transaction manager, a resource manager, an application server, and transactional applications involved in a distributed transaction system.


just-in-time reading

A synonym for indirection.

L

lazy loading

A synonym for indirection. This is the term used for indirection in the Java Persistence API (JPA).


lazy reading

A synonym for indirection.


leaf class

Has a persistent superclass in the hierarchy but does not have subclasses; queries performed on the leaf class can return only instances of the leaf class.

Compare to branch class.


locking policy

A mechanism that ensures one user does not overwrite another users's work. EclipseLink descriptors support optimistic and pessimistic locking policies.


M

mappings

Describe how individual Java objects and attributes relate to a data source.


message-driven beans

An EJB that processes asynchronous Java Messaging Service (JMS) messages. For EclipseLink clients, a message-driven bean is simply a JMS consumer with no conversational state and no home or remote interfaces.


method access

The application registers accessor methods for the attribute.

Compare to direct access.


N

named query

An EclipseLink query that is created and stored, by name, in a session for later retrieval and execution.


O

object identity

Ensures that each object is represented by one and only one instance in the application; that is, multiple retrievals of the same object return references to the same object instance, not multiple copies of the same object. Violating object identity can corrupt the object model.

See also identity map.


object-relational data type

The object-relational data type paradigm extends traditional relational databases to include object-oriented functions. Oracle, IBM DB2, Informix, and other DBMS databases allow users to store, access, and use complex data in more sophisticated ways.The object-relational data type standard is an evolving standard concerned mainly with extending the database data structures and SQL (SQL 3).

Object-relational data type descriptors describe Java objects that you map to special relational database types that correspond more closely to object types. Using these special object-relational data type database types can simplify mapping objects to relational database tables. Not all relational databases support these special object-relational data type database types.


optimistic locking

Also known as write locking; allows unlimited read access to objects. A client can write an object to the database only if the object has not changed since it was last read.

Compare to pessimistic locking.


P

packet

A piece of a message transmitted over a packet-switching network. One of the key features of a packet is that it contains the destination address in addition to the data.


packet time-to-live

A number of hops that session data packets can take before expiring. The default is 2.

See also packet.


persist

In object technology, the storage of an Java object by a data source. pessimistic locking

Objects are locked before they are edited, which ensures that only one client is editing the object at any given time.

Compare to optimistic locking.


POJO

Plain Old Java Object.

In EclipseLink, POJO means just a regular Java object model class and is used to refer to using the EclipseLink API directly rather than using EclipseLink API indirectly by way of CMP or JPA.


primary key

A field (or combination of fields) that uniquely identifies a record in the data source.


private relationship

A relationship in which the target object is considered to be a private component of the source object; the target object cannot exist without the source and is accessible only through the source object; furthermore, if the source object is destroyed, the target object is destroyed as well.

Compare to independent relationship.


proxy indirection

A type of EclipseLink indirection.

The Java class Proxy lets you to use dynamic proxy objects as place-holders for a defined interface. Certain EclipseLink mappings can be configured to use proxy indirection, which gives you the benefits of EclipseLink indirection without the need to include EclipseLink classes in your domain model or use weaving.

Q

query manager

An object, owned by a descriptor, that controls the way the descriptor accesses the database. The query manager generates its own default SQL to access the database in a transparent manner.


query optimization

EclipseLink supports two forms of query optimization: joining and batch reading. Their purpose is to optimize database access through reducing the number of database calls required to read a group of objects.


R

relationship

In EclipseLink, a reference between two EclipseLink-enabled objects.


relationship mapping

Persistent objects use relationship mappings to store references to instances of other persistent classes. The appropriate mapping class is chosen primarily by the cardinality of the relationship. EclipseLink provides five classes of relationship mappings.

Compare to direct mapping.


Remote Method Invocation (RMI)

A set of protocols that enable Java objects to communicate remotely with other Java objects.


remote session

A remote session is a client-side session that communicates over RMI with a corresponding client session and server session on the server side. Remote sessions handle object identity and marshalling and unmarshalling between client side and server side.


S

service channel

A name of the EclipseLink coordinated cache channel to which sessions subscribe in order to participate in the same coordinated cache.


session beans

EJB that represent a business operation, task, or process. EclipseLink can use session beans to make the regular Java objects they access persistent, or to wrap other legacy applications.


stale data

An artifact of caching, in which an object in the cache is not the most recent version committed to the data source.


T

transparent indirect container indirection

A type of EclipseLink indirection.

Using this type of EclipseLink indirection, you can configure indirection for any relationship attribute of a persistent class that holds a collection of related objects as any of the following:

  • java.util.Collection
  • java.util.Hastable
  • java.util.List
  • java.util.Map
  • java.util.Set
  • java.util.Vector

EclipseLink will use an indirection object that implements the appropriate interface and also performs just-in-time reading of the related objects. When using transparent indirection, you do not have to declare the attributes as ValueHolderInterface.

Newly created collection mappings use transparent indirection by default if their attribute is not a ValueHolderInterface.

For JPA entities or POJO classes that you configure for weaving, EclipseLink weaves value holder indirection for one-to-one mappings and transparent indirect container indirection for collection mappings.


U

unit of work

A transactional EclipseLink session that allows for a transaction to occur at the object level not only the database level. Changes to objects are not visible globally until the unit of work is committed.


V

value holder indirection

A type of EclipseLink indirection.

Persistent classes that use indirection must replace relationship attributes with value holder attributes. A value holder is an instance of a class that implements the ValueHolderInterface interface, such as ValueHolder. This object stores the information necessary to retrieve the object it is replacing from the database. If the application does not access the value holder, the replaced object is never read from the database. To obtain the object that the value holder replaces, use the getValue and setValue methods of the ValueHolderInterface. A convenient way of using these methods is to hide the getValue and setValue methods of the ValueHolderInterface inside get and set methods.

For JPA entities or POJO classes that you configure for weaving, EclipseLink weaves value holder indirection for one-to-one mappings and transparent indirect container indirection for collection mappings.



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