Re: [Tracker] Proposed future for Tracker - Smaller modules

[Philip Van Hoof <philip codeminded be>]

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On 8/09/2014 12:34, Martyn Russell wrote:

Hi Martyn,

> Module = tracker-store - ontology (database schema) - libstemmer
> (stemming library used by libtracker-fts) - libtracker-common (type
> and various utilities) - libtracker-data (database access and
> implementation) - libtracker-fts (SQLite module for tokenising) -
> tracker-store (daemon providing DBus interface)
>
> Module = libtracker-sparql - libtracker-bus (DBus and read/write
> access to the DB) - libtracker-direct (readonly access to the DB) -
> libtracker-sparql-backend (internal implementation) -
> libtracker-sparql (public facing library to the DB)


My proposal would be to keep tracker-store, ontology and
libtracker-sparql together (as one project).

The reason for that is that the actual goal of libtracker-sparql was
to provide what libsqlite is for a RDMBS and SQL, but for RDF and SPARQL.

Without tracker-store, libtracker-sparql can't work.

By splitting the ontologies into a separate project, managed by the
Nepomuk organization or not, we could someday refactor
libtracker-sparql to support multiple instances of installed ontologies.

Ideal in that scenario would be that tracker-store becomes an impl.
detail of libtracker-sparql (it'll manage the instances of stores on a
on-demand basis).

The only real three reasons of existence of tracker-store are:

        - GraphUpdated
        - The fact that SQLite isn't MVCC and we need WAL journaling
          and checkpointing done by a separate 'writer' process
        - Providing a ontology

When your process links with libtracker-sparql and uses direct-access
mode, it effectively has everything it needs to deal with meta.db.

The eventual dependency tree would look like this:

Your program depends on:
|
+- nepomuk-ontology
|
+-libtracker-sparql
  `- Internally uses libexec/tracker-sparql-store

This API:

https://developer.gnome.org/libtracker-sparql/stable/TrackerSparqlConnection.html

Would look like:

#include <nepomuk/2006-2008/ontology.h>
#include <tracker-sparql.h>

static void something ()
{
  GError *error = NULL;
  Ontology *ontology = nepomuk_ontology_2006_2008_new ("session id");
  TrackerSparqlConnection *con =
        tracker_sparql_connection_get_for_ontology (ontology)
  TrackerSparqlCursor *cursor = tracker_sparql_connection_query (con,
                "select ?a { ?a nie:title 'something in nepomuk' }",
                NULL, &error);


  while (tracker_sparql_cursor_next (cursor, NULL, NULL)) {
        g_print ("%s\n", tracker_sparql_cursor_get_string());
  }

  g_object_unref (cursor);
  g_object_unref (con);
  g_object_unref (ontology);
}

This would internally deal with starting and stopping a
libexec/tracker-sparql-store, and no global "tracker-store" would be
needed anymore (the fact that multiple users share the same "session
id", creates the central storage for users of that "session id").

Storage could go to:
~/.tracker/sessions/$session-id/nepomuk-2006-2008/meta.db or something

Kind regards,

Philip

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