Github user afs commented on the issue:
https://github.com/apache/jena/pull/274
This adds `NamedGraph` - a graph wrapper that carries around a graph name.
The problem is now that graphs in a general dataset only have an associated
name by virtue of the slot in the map they occupy, unlike ones from a quad
dataset where the graph is a `GrahView`, a restriction of the "G" slot of the
quad to a specific name.
The updated test case on
[JENA-1381](https://issues.apache.org/jira/browse/JENA-1381) shows this - it
tests three kinds of dataset in memory.
| Dataset factory | Implementation | Characteristics | Status (before PR) |
| --------------- | -------------- | --------- | ---- |
| `create()` | `DatasetGraphMap` | Copy-in on add graph | No
graph index |
| `createGeneral()` | `DatasetGraphMapLink` | Link to added graphs | No
graph index |
| TIM | Quads | `getGraph` returns a `GraphView` | OK |
| TDB | Quads | `getGraph` returns a `GraphView` | OK |
**`create()`** : `DatasetGraphMap` can change to use a `NamedGraph` by
changing the `GraphMaker` interface to take a name and then using
`NamedGraphWrapper` aroudn an in-memeory graph.
**`createGeneral()`** : `DatasetGraphMapLink` can either change to return a
`NamedGraph` which mean
the graph returned by `getGraph` is not the graph added, or can remain not
supporting test query graph. The general dataset is already less aligned with
the other implementations and can be considered "special purposes only" -
usually complex mixtures of graph types or inference graphs.
The javadoc for `DatasetFactory` is supposed to discourage use of the
linking `createGeneral`.
The recent commits provide this and update the javadoc in `DatasetFactory`.
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