Glossary

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

attribute

A variable of a class or object. In OracleAS TopLink, attribute describes all instance variables of a class. Every attribute contains a single mapping.

bean class

The implementation of the bean. The bean is accessed from the client using the home and remote interfaces.

branch class

A class that consists of 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.

class

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

class indicator field

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

custom SQL

Any non-OracleAS TopLink-generated SQL used through OracleAS TopLink. This includes hard-coded SQL and stored procedure calls.

Data Definition Language (DDL)

A language that is a part of the SQL. OracleAS TopLink Mapping Workbench can generate DDL scripts that can be used to create tables on the desired database.

dependent classpath

A location where non-bean classes are specified. OracleAS TopLink requires that the bean classes be included here as they are referenced by the project.

descriptor

An OracleAS TopLink object that describes how the attributes and relationships of an object are to be represented in relational database tables. An OracleAS TopLink descriptor is not the same as a deployment descriptor, although it plays a similar role.

direct access

By default, OracleAS TopLink 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 attributes type, then it must be transformed on its way to and from the database

OracleAS TopLink provides five classes of direct mappings.

Compare to relationship mapping.

expressions

The OracleAS TopLink equivalent of an SQL conditional clause

OracleAS TopLink expressions are specified using the Expression and ExpressionBuilder classes.

identity map

A map used to cache objects for performance and to maintain object identity.

Compare to 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

An indirection object is one that acts as a stand-in for another object. In OracleAS TopLink, indirection is implemented through Value Holders, which delay database access by acting as stand-ins for any object relationships.

inheritance

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

J2SE

The Java 2 Platform, Standard Edition (J2SE) is the core Java technology platform. It provides software compilers, tools, runtimes, and APIs for writing, deploying, and running applets and applications in Java.

J2EE

The Java 2 Platform, Enterprise Edition (J2EE) is an environment for developing and deploying enterprise applications. J2EE includes a set of services, APIs, and protocols for developing multi-tier Web-based applications.

J2EE containers

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

Java Data Objects

Java Data Objects (JDO) represent a standard Java model for persistence that enables programmers to create code in Java that transparently accesses the underlying data store without using database-specific code. OracleAS TopLink provides support for most of the JDO specification, however, because OracleAS TopLink is a persistence framework, you may find it easier and more effective to build your applications using OracleAS TopLink functionality rather than JDO.

Java Transaction API Support

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.

leaf class

A 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.

method access

The application registers accessor methods for the attribute.

Compare to direct access.

object identity

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

Compare to identity map.

optimistic locking

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

Compare to pessimistic locking.

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.

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. In addition, if the source object is destroyed, then the target object is destroyed as well.

Compare to independent relationship.

Project Tree

The main interface of OracleAS TopLink Mapping Workbench. The Project Tree shows the high-level information stored in a project.

query manager

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

query optimization

OracleAS TopLink supports two forms of query optimization, joining and batch reading. Their purpose is to optimize database access by reducing the number of database calls required to read a group of objects.

relationship

In OracleAS TopLink, a reference between two OracleAS TopLink-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. OracleAS TopLink provides five classes of relationship mappings.

Compare to direct mapping.

unit of work

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

value holder

A wrapping object used by OracleAS TopLink to delay database access.