Add support for dynamic fields

[GoogleCodeExporter]

The following proposal suggests the addition of "dynamic fields" (I use this 
name because the suggested feature is somewhat similar to the same feature in 
Apache Solr).

The addition of this feature is required to use LDPath instead of the current 
[Mapping language](http://wiki.iks-project.eu/index.php/RepresentationMapping) 
within the [Apache Stanbol 
Entityhub](http://incubator.apache.org/stanbol/docs/trunk/entityhub.html).

### Dynamic Field and LDPath (proposal)

Currently ldpath only field definitions like

    FIELDNAME = PATH :: FIELDTYPE FIELDCONF

Dynamic fields would allow

    FIELD_PREFIX* = PATH_PREFIX* [:: FIELDTYPE FIELDCONF]


The typical usecase would be to select all properties of a given namespace

   dc_* = dc:* :: xsd:string

Adding this would greatly improve the useability of the already existing 
Wildcard support.

NOTE: While I am using here '*' in the sense of Wildcards one could also 
imaging to allow other kind of pattern definitions.

### Dealing with conflicts

A conflict is of the FIELDNAME of a normal field is the same as 
FIELD_PREFIX{suffix}.

In such cases the statically configured Pattern for FIELDNAME MUST HAVE 
precedence.

e.g. the program

    dc_* = dc:* :: xsd:string
    dc_title = dc:title[@en] :: xsd:string

MUST only select English titles.


### Implementation:

I would suggest to add a 

    listProperties(Node context)

to RDFBackend. This would allow the NodeSelector to filter properties of an 
node against the defined pattern.

Original issue reported on code.google.com by [email protected] on 5 Dec 2011 at 12:13