Platforms

Java	J2EE J2SE Android (Open Handset Alliance) Supported Frameworks: Spring, OSGi, DataNucleus, Restlet, Griffon, Guice
.NET	.NET Framework (3.5, 4.0) .NET Compact Framework (2.0-3.5) Windows (XP, Vista) Windows Mobile / PocketPC, Windows Phone Mono (partial) Supported Frameworks: Castle, Eiffel, Spring.net

Languages

Java	JDK 5+ Scala
.NET	C# Visual Basic

Commands

Sessions	Start and end
Database files	Create, open, close, and delete
Transactions	Commit and Rollback
Objects	Store, retrieve, update (incl. cascaded), replicate, delete (incl. cascaded)
Messaging	TCP/IP

Transparency

Language constructs	Primitive types Strings Arrays Multi-dimensional arrays Inner classes Java/C# collections Classes without public constructors .NET structs Blobs (stored outside of DB file)
Non-Intrusive	Without deriving from a specific base class Without implementing a specific interface Without modifications to source code Without implementing Serializable
Private Fields	Storable
File I/O	Pluggable
Reflector	Pluggable Generic
Aliases	Class aliasing for class-to-class mappings
Transparent Persistence	Programmatic or via byte-code instrumentation

Query Languages / APIs

Object oriented	LINQ Native Queries (NQ) Query By Example (QbE) S.O.D.A.
SQL	Only via replication to many relational databases With Third-Party products (e.g. DataNucleus' Sql4o)
XML	With Third-Party products (e.g., Xstream)

Modes / Concurrency

Operation Modes	Local Client/Server
Threads	Multiple
Transactions	Multiple, parallel
Semaphores	Available
Read-Only Mode	Available

Scalability and Performance

Performance benchmark	Up to 55x faster than Hibernate/MySQL See PolePosition open-source benchmark
In-Memory Mode	Available
Client-side	Single-process execution available
Server-side	Server-side query execution available
DB-aware Collections	Available
Object Caching	Available
Pagination	Server-side cursors (lazy queries)
Indexing	BTree field indexes
BTree Query Processor	Big Sets

Replication

db4o Replication System (dRS)	100% object-oriented: simply replicate objects, not tables Uni- and bi-directional db4o to db4o db4o to relational databases (RDBMS), via Hibernate (Java only) db4o to Versant Object Database (VOD, Java only)
UUID	Unique Universal Identity over all DB instances
Synchronization	Querying Update Delete Conflict resolution

Reporting

For Java objects	Actuate BIRT Elixir Report Jaspersoft JasperReports Jinfonet JReport
For .NET objects	Microsoft Visual Studio ReportViewer

Security and Encryption

DB file Encryption

Pluggable File I/O for custom encryption With Third-Party products (e.g. XTEA)

Availability, Reliability, Zero-Admin

Transactions	ACID Commit-recovery on system failures
Thread Safety	Available
Automatic Recovery	Available
Online-Backup	Available
Free Space Management	Defragmentation API available

Internationalization

Unicode

Available

Refactoring

Schema Versioning	Automatic recognition and maintenance
Renaming	Classes, fields by API Access to values of removed fields by API or with ObjectManager UI

Memory and File Size

DB library footprint	~1 MB
Minimal RAM footprint	Application-dependent; deterministic; typically < 3 MB
Maximum DB file size	254 GB / database file