Contains the core classes that provide the implementation of the JCR API.

The following table lists the core JCR interfaces and the corresponding Jackrabbit implementation classes found in this package.

JCR interfaces and Jackrabbit implementations
JCR interface | Implementation class
--- | ---
{@link javax.jcr.Repository Repository} | {@link org.apache.jackrabbit.core.RepositoryImpl RepositoryImpl}
{@link javax.jcr.Session Session} | {@link org.apache.jackrabbit.core.SessionImpl SessionImpl}
{@link javax.jcr.Workspace Workspace} | {@link org.apache.jackrabbit.core.WorkspaceImpl WorkspaceImpl}
{@link javax.jcr.Item Item} | {@link org.apache.jackrabbit.core.ItemImpl ItemImpl}
{@link javax.jcr.Property Property} | {@link org.apache.jackrabbit.core.PropertyImpl PropertyImpl}
{@link javax.jcr.Node Node} | {@link org.apache.jackrabbit.core.NodeImpl NodeImpl}

A Jackrabbit repository instance can be created using the static {@link org.apache.jackrabbit.core.RepositoryImpl#create(org.apache.jackrabbit.core.config.RepositoryConfig) RepositoryImpl.create(RepositoryConfig)} method. Classes in the {@link org.apache.jackrabbit.core.jndi org.apache.jackrabbit.core.jndi} package provide a mechanism for binding a Jackrabbit repository in a JNDI directory context.

A `SessionImpl` instance is created upon successfully login to the `Repository` (see `Repository#login(Credentials, String)`).

A `Session` is always tied to the `Workspace` specified in the `Repository#login(Credentials, String)` call. A workspace represents a persistent tree of repository items (i.e. `Node`s and `Property`s). The items in a workspace are 'visible' to all sessions accessing it (subject to their access rights, of course). A `WorkspaceImpl` instance represents a specifc workspace as seen by the session that accesses it.

Every repository item is uniquely identified by its `ItemId`. The id of a node (`NodeId`) consists of the node's uuid. The id of a property (`PropertyId`) consists of the parent node's uuid and the name of the property.

## Item managers

Every `SessionImpl` instance has its own `ItemManager`. The per-session instance of `ItemManager` acts as item factory (i.e. it creates `NodeImpl` and `PropertyImpl` instances) and provides item access by item id and item caching.

The data (or state) of an item is represented by the following classes in the subpackage `state`:

- {@link org.apache.jackrabbit.core.state.ItemState ItemState}
- {@link org.apache.jackrabbit.core.state.PropertyState PropertyState}
- {@link org.apache.jackrabbit.core.state.NodeState NodeState}

There's one `SharedItemStateManager` for every workspace. It provides item state caching and it guarantees that there's only one (persistent) item state instance for any distinct item id in that workspace.

Every session has its own `SessionItemStateManager` that consists of the session's `TransientItemStateManager` and the workspace's `SharedItemStateManager`.

Each item (i.e. `NodeImpl` and `PropertyImpl`) instance is holding an `ItemState` instance. When e.g. a session is modifying a property by changing the property's value, a new transient item state is created by the session's `TransientItemStateManager`. This transient state is actually wrapping the (old) shared state (copy on write). The `PropertyImpl`'s state is then replaced by the new transient state.

Transient (i.e. unsaved) modifications are 'session-local', i.e. they are not visible to other sessions. When the modifications are saved they become instantly visible to all sessions accessing the same workspace.