[Gzz] PEG model_management--tjl

[Tuomas Lukka]

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PEG model_management--tjl: What are Spaces in the new system?
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:Author:   Tuomas J. Lukka
:Last-Modified: $Date: 2003/04/02 17:03:07 $
:Revision: $Revision: 1.1 $
:Status:   Incomplete

The Space system was hastily ported from Gzz for the demo deadline.
It needs rethinking.

Issues
======

- What are the relevant concepts in this PEG?

    RESOLVED:
        
        - RDF Model

        - RDF Node

        - Node content

        - Xanalogical transclusions

        - Xanalogical links

- Why the abbreviated name?
    
    RESOLVED: This is a name that will be written SO often
    that acronymizing it is appropriate. All views &c will
    carry an instance of this class.

- Do we really need the "home" member in FFC?

Introduction
============

First, let's reiterate some important differences from Gzz's Space construction.
In Gzz, a Cell was bound to its Space, and Space also provided the facilities 
for
getting a Cell's content.

In Jena, the situation is dramatically different. Actually, I think it's better;
more natural for RDF at least. RDF nodes and RDF statements are completely 
independent of the Model, and the RDF Model ("space") is just a collection
of Statements, with some optimizations.

For Fenfire, we do still need some abstract notion of a node's content; 
basically,
a mapping between nodes and enfilades, as well an index for use in xu links.
One alternative would be to wrap RDFNodes into Cell-like objects but that would
be very inefficient as well as inelegant.

Changes
=======

I propose the following FFC (FenFire Context) class::

    package org.fenfire;

    class FFC {
        public jena.Model model;
        RDFNode home; 

        NodeContent content;
        
        EnfiladeOverlapIndex enfiladeOverlap;
        XuIndexer xuLinks;
    }

(replace ``jena.`` by ``com.hp.hpl.mesa.rdf.jena.model.``)
This class would be frozen at birth.
at the same time, remove for now IndexManager.

The org.fenfire.NodeContent interface is defined as follows::

    class NodeContent {
        /** Get the vstream in this cell.
         *  Never returns <code>null</code>.
         */
        Enfilade1D getEnfilade(RDFNode node);

        /** Set the vstream in this cell.
         */
        void setEnfilade(RDFNode node, Enfilade1D vstream);
    }

This class would also be frozen.

The classes EnfiladeOverlapIndex and XuIndexer would also be frozen.