Connected Data Objects
# Connected Data Objects

Connected Data Objects (CDO) is a free implementation of a Distributed Shared Model on top of the Eclipse Modeling Framework (EMF).

With CDO, programmers can easily enhance existing EMF models in such a way that they can be stored and subsequently maintained in a central model repository. While object relational mapping against a JDBC data source on the server side is the shipped default, CDO provides for pluggable storage adapters that allow you to develop and use different mappers (like Hibernate- or OODB-based). On the client side, CDO provides a default integration with EMF, the Eclipse Modeling Framework, although other model integrations on top of the CDO protocol are imaginable as well.

## Model integration features

* EMF integration at model level (as opposed to the edit level)
* Support for generated models (just switch two .genmodel properties)
* Support for dynamic models (just load .ecore file and commit to repository)
* Support for legacy models (for compiled models without access to .genmodel)
* Support for the Ecore meta model and descendants

## User interface features

* Eclipse view for working with CDO sessions, transactions, views and resources
* Package Manager dialog per session
* Eclipse editor for working with resources and objects

## Client side features

* Multiple sessions to multiple repositories on multiple servers
* Multiple transactions per session
* Multiple read-only views per session
* Multiple audit views per session (an audit is a view that shows a consistent, historical version of a repository)
* Multiple resources per view (a view is always associated with its own EMF ResourceSet)
* Inter-resource proxy resolution
* Multiple root objects per resource
* Object state shared among all views of a session
* Object graph internally unconnected (unused parts of the graph can easily be reclaimed by the garbage collector)
* Only new and modified objects committed in a transaction
* Transactions can span multiple resources
* Demand loading of objects (resources are populated as they are navigated)
* Partial loading of collections (chunk size can be configured per session)
* Adaptable pre-fetching of objects (different intelligent usage analyzers are available)
* Asynchronous object invalidation (optional)
* Clean API to work with sessions, views, transactions and objects
* CDOResources are EObjects as well
* Objects carry meta information like id, state, version and life span
* Support for OSGi environments (headless, Eclipse RCP, ...)
* Support for standalone applications (non-OSGi)

## Network protocol features

* Net4j based binary application protocol
* Pluggable transport layer (shipped with NIO socket transport and JVM embedded transport)
* Pluggable fail over support
* Pluggable authentication (shipped with challenge/response negotiation)
* Multiple acceptors per server

## Server side features

* Pluggable storage adapters
* Multiple repositories per server
* Multiple models (packages) per repository
* Multiple resources (instance documents) per repository
* Expressive XML configuration file
* Configurable storage adapter per repository (see below)
* Configurable caching per repository
* Clean API to work with repositories, sessions, views, transactions and revisions
* Support for OSGi environments (usually headless)
* Support for standalone applications (non-OSGi)

## DB store features

* Supports all optional features of the CDO Server
* Pluggable SQL dialect adapters
* Includes support for Derby, HSQLDB, MySQL and Oracle (TBD)
* Pluggable mapping strategies
* Includes horizontal mapping strategy (one table per concrete class)
* Includes vertical mapping strategy (TBD, one table per class in hierarchy)
* Supports different mapping modes for collections
