Which Persistence Specification ?

http://db.apache.org/jdo/jdo_v_jpa.html

There are several competing persistence technologies available for Java. Two of these are "standardised" (via the JCP). When developing your application you need to choose the most appropriate technology for your needs. Java Data Objects (JDO) has been a standard since 2001 with the release of JDO1. It was improved with the release of JDO2. Just to confuse issues the Java Persistence API (JPA) was approved in its JPA1 form, and JDO2.1/JDO2.2 provide updates to JDO2 building on some of the new features of JPA1. Since then we have had JDO3 adding on extra metadata and enhancer standardisation, JPA2 providing criteria queries and JPA2.1 adding some further features. Below we show some of the differences of these 2 standards to give you assistance in selecting what you need. Highlighted in bold are the notable differences where one specification provides something not available in the other.

Feature	JDO	JPA
JDK Requirement	1.3+	1.5+
Usage	J2EE, J2SE	J2EE, J2SE
Persistence specification mechanism	XML, Annotations, API	XML, Annotations
Datastore supported	Any	RDBMS only
Restrictions on persisted classes	no-arg constructor (could be added by compiler/enhancer)	No final classes. No final methods. Non-private no-arg constructor. Identity Field. Version Field.
Ability to persist "transient" fields	Yes	No
Persist static/final fields	No	Not specified
Transactions	Pessimistic, Optimistic	Optimistic, some locking
Object Identity	datastore-identity, application-identity	application-identity
Object Identity generation	Sequence, Table, Identity, Auto, UUID String, UUID Hex	Sequence, Table, Identity, Auto
Change objects identity	Throw exception when not allowed	Undefined !!
Supported types	Java primitive types, wrappers of primitive types, java.lang.String, java.lang.Number, java.math.BigInteger, java.math.BigDecimal, java.util.Currency, java.util.Locale, java.util.Date, java.sql.Time, java.sql.Date, java.sql.Timestamp, java.io.Serializable, boolean[], byte[], char[], double[], float[], int[], long[], short[], java.lang.Object, interface, Boolean[], Byte[], Character[], Double[], Float[], Integer[], Long[], Short[], BigDecimal[], BigInteger[], String[],PersistenceCapable[], interface[], Object[], Enums, java.util.Collection, java.util.Set, java.util.List, java.util.Map,Collection/List/Map of simple types, Collection/List/Map of reference (interface/Object) types, Collection/List/Map of persistable types	Java primitive types, wrappers of the primitive types, java.lang.String, java.math.BigInteger, java.math.BigDecimal, java.util.Date, java.util.Calendar, java.sql.Date, java.sql.Time, java.sql.Timestamp, java.io.Serializable, byte[], Byte[], char[], Character[], Enums, java.util.Collection, java.util.Set, java.util.List, java.util.Map Collection/List/Map of persistable types
Embedded Fields	Embedded persistent objects, Embedded Collections, Embedded Maps	Embedded persistent objects
Access a non-detached field	Throw exception	Undefined !!
Inheritance	Each class has its own strategy	Root class defines the strategy
Operation cascade default	persist, (delete)
Operation Cascade configuration	delete	persist, delete, refresh
Query Language	JDOQL, SQL, others	JPQL, SQL
Query candidates	Candidate without subclasses, Candidate and its subclasses	Candidate and its subclasses
Query of candidate collection	yes	no
Query language case sensitivity	JDOQL lowercase/UPPERCASE	JPQL case-insensitive
Query language aliases	No, but has variables in JDOQL	Yes in JPQL
Query Criteria API	No, available as extension in QueryDSL	Yes
Object retrieval control	Lazy/Eager control, fetch groups	Lazy/Eager control, entity graphs
Bulk update/delete	JDOQL Bulk Delete	JPQL Bulk Delete, JPQL Bulk Update
RDBMS Schema Control	Tables, columns, PK columns, PK constraints, FK columns, FK constraints, index columns, index constraints, unique key columns, unique key constraints	Tables, columns, PK columns, FK columns, unique key columns
ORM Relationships	Full range of Collection, Map, List, Array, 1-1, 1-N, M-N using PC, Non-PC and interface objects	Basic 1-1, 1-N, M-N, Collection, Map
Default ORM column size	256	255
Default ORM identifiers (tables/columns)	No	Yes
Default ORM mappings	Yes, JDBC types defined for Java types	No
Caching interface	L2 Caching API	L2 Caching API

As an overall conclusion "JPA" is a subset of what is available in "JDO".