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From Alex Karasulu <akaras...@apache.org>
Subject Re: Some thoughts about the SchemaObjects
Date Fri, 03 Feb 2012 23:21:01 GMT
On Thu, Feb 2, 2012 at 10:10 PM, Emmanuel Lecharny <elecharny@gmail.com>wrote:

> For the former issues, which has been raised when we started to try to
> extend the API to allow a user to add new Schema elements locally, we think
> that we must modify the current data structure for schema objects.
>
> Here are a few brain dump and some examples :
>
> First, the SchemaManager will only manage immutable SchemaObjects (ie,
> here, AttributeType), as there is no reason to allow someone to pull a
> SchemaObject from the SchemaManager and to modify it on the fly. That would
> be destructive for the sc hemaManager user, as it may impact other users.
>
>
Right you don't want to mess with the in memory structure (graph of schema
objects) that is managed by the schema manager directly.


> Now, for Studio, being able to pull an AT from teh SM, modify this AT and
> inject it back to the SM is useful.
>

Yes for the schema editor we've discussed this a couple times.


>
> We then discussed about Mutable and Immutable schema objects, and how they
> can help us solving this issue.
>
> If a user want to modify an existing SchemaObject pulled from the
> SchemaManager must first make it mutable :
>
> AttributeType attributeType = schemaManager.**getAttributeType(
> "2.5.4.11" );
> MutableAttributeType mat = new MutableAttributeType( attributeType );
>
> In this case, the resulting instance is a copy of the initial immutable
> object.
>
>
Will the mutable will track the differences (the deltas) in the mutable
from the original schema object being wrapped?


> In order to be able to implement such a proposal, the following hierarchy
> could be enough :
>
>
>   (SchemaObject)<---------------**----(MutableSchemaObject)
>         o                                     ^
>         |                                     |
> {AbstractSchemaObject}                         |
>         ^                                     |
>         |                                     |
>   [AttributeType]<--------------**----[MutableAttributeType]
>
>
>
> where (III) are interfaces, {AAA} are abstract classes and [CCC] are
> normal classes.
>
> The base implementation is :
>
> o (SchemaObject) expose all the SO getters.
> o (MutableSchemaObject) interface expose the SO setters.
> o {AbstractSchemaObject} implements the the SO getters
> o [AttributeType] implements the AttributeType getters
> o [MutableAttributeType] implements the AttributeType setters
>
>
With you here.


> (see an exemple at the end of this mail)
>
> With those classes and interface, it's possible to hide the setters for a
> user manipulating an AT he got from the SchemaManager, but this user has
> the possibility to modify this AT by wrapping it into a new MutableAT.
>
> In order to create new SchemaObject, a user can :
>
> 1) create a MutableSchemaObject, and get its immutable copy :
>
> MutableAttributeType mutableAT = new MutableAttributeType();
> mutableAT.setXXX( yyy );
> ...
> AttributeType attributeType = new AttributeType( mutableAT );
>
> 2) create a new AttributeType using the RFC notation :
>
> AttributeType attributeType = new AttributeType( "( 2.5.4.58 NAME '**attributeCertificateAttribute'
> DESC 'attribute certificate use ;binary' SYNTAX
> 1.3.6.1.4.1.1466.115.121.1.8 )" );
>
> In any case, everything stored in the SchemaManager must be immutable.
>
>
>
SNIP


> Thoughts ?
>
>
I would like to share a view I have in my head about all the in memory
schema data structures we have. Just a quick review as some points/facts
first:

(1) We have schema objects that directly reference other schema objects
resulting a graph of schema objects.

(2) The designed model of schema objects let's the containment hierarchy
naturally walk the graph. Like for example looking at the MAY list of an
ObjectClass will reference actual AttributeType objects in the graph
connected to the ObjectClass. Further walking the AT object to see it's
Syntax and MatchingRules does the same.

(3) Registry objects serve as map structures for rapidly indexing into
pools of schema objects by type based on alias names and their OID.

NOTE:
Contained objects like a Syntax referenced by an AttributeType should not
be directly referenced. Instead the Syntax's OID should be kept in the
AttributeType and an accessor like getSyntax() should use a lookup via the
Syntax Registry. This is important from both an OSGi standpoint and to
easily implement a change mechanism to this grand data structure atomic,
consistent and isolated.

----

I like the Mutator wrappers introduced in this mail thread above: and I
think it's key to implement a proper change algorithm. I also like the idea
of them serving to just store deltas and track changes from the original
immutable objects that they directly reference. This probably will make the
schema editor code a lot easier to implement.

I see a set of mutators being collected/tracked as a group, then applied in
an atomic batch to the main data structure after a validation test to
determine if the resultant graph is consistent. Then the entire structure
can be read and write locked, and changes to it from the mutators applied
throughout, then the structure unlocked. The full structure locking for
readers and writers is acceptable since we rarely perform schema change
operations and it maintains a consistent view.

We should also fire some events to inform those that need to listen to
schema changes that something was altered. Sending those listeners the
deltas or mutator objects might be valuable for them to refresh themselves.

Thoughts?

-- 
Best Regards,
-- Alex

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