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From "Alex Karasulu" <akaras...@apache.org>
Subject [BigBang] [ApacheDS] Progress report
Date Mon, 31 Dec 2007 19:24:37 GMT
Hello,

I am posting the conclusions of my conversations yesterday with Emmanuel
regarding the ServerEntry API and various related matters here for tracking
and availability to the community.  Also I am adding additional information
on how far we have progressed in phase II.


Background
=========

The Entry API is a new programming interface for managing entries, their
attributes and the values in those attributes.  This API is going to replace
the JNDI interfaces (Attribute and Attributes) we were using up until this
point as part (phase II) of the big bang refactoring initiative.  We have
discovered several shortcomings with using JNDI interfaces and one of them
deals with how entries, attributes and values are managed.  The server-side
specific extension is a ServerEntry.  Unlike JNDI interfaces it's interfaces
are DN and schema aware.  These new interfaces are designed to prevent
anomalies that result with attribute and value containment when schema is
not properly consulted.

Likewise we are replacing other JNDI constructs like the NamingEnumeration
with a new interface that is better suited to operations within the lower
data handling layers of the server.  The Cursor interface is the new
interface that will replace NamingEnumerations.  This API is more
specifically geared towards our needs and prevents several issues we've
faced with the JNDI NamingEnumeration interface which is generalized to
accommodate every naming system that SUN could think of.


ServerEntry Factory
==============

A ServerEntry requires knowledge of schema information to make sure things
like, removal, addition and value lookups occur properly.  A ServerEntry
extends Entry.  The LDAP codec which could operate on a client or on a
server must [de]marshal LDAP PDU's into these objects.  Rather than
instantiate these objects itself we realized that it is best off delegating
instantiation to some kind of factory which can be handed to it.  This way
if in a server the proper kinds of entries with schema knowledge are created
transparently, and on the client side schema a different kind of factory can
be used which does not need schema information.

We have a bit of a chicken and egg problem while configuring the server.
The server needs ServerEntry instances for the RootDSE and for the root of
partitions (the namingContexts).  To start the server some minimum of schema
information is required.  For this reason we plan to make the
DirectoryService either extend the EntryFactory interface or have it contain
a reference to an EntryFactory implementation.  Further more the default
constructor on the DefaultDirectoryService will initialize the bootstrap
schemas needed to minimally startup the server so it can initialize
properly.  This way the DirectoryService object or it's contained
ServerEntryFactory will be able to instantiate ServerEntry objects on behalf
of requestors with a means to access at least a minimal set of schema
information.

Emmanuel and I were debating whether to use containment or inheritance.  I
prefer containment myself but Emmanuel pointed out that the interface for
ServerEntryFactory is simple and has a single method.  So perhaps having
DirectoryService extend this interface for now is more pragmatic.  If the
interface grows we can re-factor and use containment instead.  Emmanuel can
comment but I think he wants to avoid calls like:

directoryService.getEntryFactory().newEntry( new LdapDN( "..." ) );

Instead with extension we would have:

directoryService.newEntry( new LdapDN( "..." ) );

So the later looks like a cleaner approach.  I will soon implement this.  I
already committed a portion of this in this revision:

    http://svn.apache.org/viewvc?view=rev&revision=607763


Cursor API Progress
===============

I guess most of you see the commit messages go by and notice that I am
working in my sandbox on the Cursor API which is to replace the use of
NamingEnumerations in the core.  I did this so I would not break many things
in the big bang which some of you are working on.  This has not progressed
as rapidly as I wanted it to.  However there are some deep changes that will
impact several aspects of the server and the way it conducts search
operations so this is not a simple matter.

I do have what feels like an almost complete interface.  The Cursor is
working well and solving several issues that we have had with
NamingEnumerations.  It will also allow us to eventual (after 2.0 I guess)
move the search algorithm out of the Partitions.  There are also several
freedoms that come with this new API that I am discovering as I use it
specifically because it is bidirectional with next() and previous() methods
unlike the NamingEnumeration which is not.

Right now I am really worried about the impact this has on the server.  It
takes a lot for me to branch privately so I may abandon this work if the
next week or two does not make me more confident.

Alex

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