more info on NotifyingSail

Signed-off-by: Jeen Broekstra <jeen.broekstra@gmail.com>

Author: abrokenjester

doc/sail/index.adoc

@@ -178,9 +178,9 @@ The abstract base classes use the naming convention ``methodname**Internal**`` t
 
 For example, the query method `AbstractSailConnection.getStatements()` provides a lot of book keeping: it ensures pending updates are flushed, acquires a read lock on the connection, verifies the connection is still open, and takes care of internally registering the resulting `Iteration` from the query for resource management and concurrency purposes. In between all of this, it calls `getStatementsInternal`. The only job of this method is to answer the query by retrieving the relevant data from the data source.
 
-=== NotifyingSail and NotifyingSailConnection
+=== NotifyingSail and AbstractNotifyingSail
 
-The `NotifyingSail` and `NotifyingSailConnection` interfaces provide basic event handling for SAIL implementations. Its main goal is to provide a messaging mechanism for closely-linked SAIL implementations (for example, a "Sail stack" where a reasoner is to be kept informed of changes to the underlying database). 
+The `NotifyingSail` and `NotifyingSailConnection` interfaces provide basic event handling for SAIL implementations. The main goal of these interfaces is to provide a messaging mechanism for closely-linked SAIL implementations (for example, a "Sail stack" where a reasoner is to be kept informed of changes to the underlying database). 
 
 .NotifyingSail interfaces
 [[figure-notifying-sail]]
@@ -213,18 +213,28 @@ interface SailConnectionListener {
     + statementRemoved(Statement st)
 }
 
+abstract class AbstractNotifyingSail
+abstract class AbstractNotifyingSailConnection
 Sail <|-- NotifyingSail
 SailConnection <|-- NotifyingSailConnection
-NotifyingSail *-- NotifyingSailConnection
-NotifyingSail - SailChangedListener
-SailChangedListener - SailChangedEvent
-NotifyingSailConnection - SailConnectionListener
+NotifyingSail "1" *- "*" NotifyingSailConnection
+NotifyingSail "0..1" o-- "*" SailChangedListener
+SailChangedListener -d- SailChangedEvent
+NotifyingSailConnection "0..1" o- "*" SailConnectionListener
+
+AbstractNotifyingSail -u-|> NotifyingSail
+AbstractNotifyingSail -u-|> AbstractSail
+AbstractNotifyingSailConnection -u-|> NotifyingSailConnection
+AbstractNotifyingSailConnection -r-|> AbstractSailConnection
 ....
 
 As can be seen in diagram <<figure-notifying-sail>>, the `NotifyingSail` interface provides the option of registering one or more `SailChangedListener` implementations. When registered, the listener will be messaged via the `sailChanged` method. The contents of the message is a `SailChangedEvent` that provides basic info on what has been changed.
 
 More fine-grained event data is available at the Connection level. The `NotifyingSailConnection` allows registering a `SailConnectionListener`, which receives a message for each individual statement added or removed on the connection. 
 
+RDF4J also provides base implementation classes for these two interfaces. As can be seen in diagram <<figure-notifying-sail>>, these classes - `AbstractNotifyingSail` and `AbstractNotifyingSailConnection` - are extensions of the AbstractSail(Connection) classes that add 
+default implementations of the methods defined in the NotifyingSail(Connection) interfaces.
+
 === StackableSail
 
 TODO