Overview.java

/*
 * Copyright (c) 2011-2013, 2015, 2016 Eike Stepper (Berlin, Germany) and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *    Eike Stepper - initial API and implementation
 */
package org.eclipse.emf.cdo.doc;

import org.eclipse.emf.cdo.server.IPermissionManager;

import org.eclipse.net4j.util.security.IAuthenticator;

/**
 * Overview
 * <p>
 * CDO is a pure Java <i>model repository</i> for your EMF models and meta models. CDO can also serve as a
 * <i>persistence and distribution framework</i> for your EMF based application systems. For the sake of this overview a
 * model can be regarded as a graph of application or business objects and a meta model as a set of classifiers that
 * describe the structure of and the possible relations between these objects.
 * <p>
 * CDO supports plentyfold deployments such as embedded repositories, offline clones or replicated clusters. The
 * following diagram illustrates the most common scenario: <p align="center">{@image cdo-overview.png}
 *
 * @default
 * @author Eike Stepper
 */
public class Overview
{
  /**
   * Functionality
   * <p>
   * The main functionality of CDO can be summarized as follows:
   * <dl>
   * <dt><b>Persistence</b>
   * <dd>Persistence of your models in all kinds of database backends like major relational databases or NoSQL
   * databases. CDO keeps your application code free of vendor specific data access code and eases transitions between
   * the supported backend types.
   * <p>
   * <dt><b>Multi User Access</b>
   * <dd>Multi user access to your models is supported through the notion of repository sessions. The physical transport
   * of sessions is pluggable and repositories can be configured to require secure authentication of users. Various
   * authorization policies can be established programmatically.
   * <p>
   * <dt><b>Transactional Access</b>
   * <dd>Transactional access to your models with ACID properties is provided by optimistic and/or pessimistic locking
   * on a per object granule. Transactions support multiple savepoints that changes can be rolled back to. Pessimistic
   * locks can be acquired separately for read access, write access and the option to reserve write access in the
   * future. All kinds of locks can optionally be turned into long lasting locks that survive repository restarts.
   * Transactional modification of models in multiple repositories is provided through the notion of XA transactions
   * with a two phase commit protocol.
   * <p>
   * <dt><b>Transparent Temporality</b>
   * <dd>Transparent temporality is available through audit views, a special kind of read only transactions that provide
   * you with a consistent model object graph exactly in the state it has been at a point in the past. Depending on the
   * chosen backend type the storage of the audit data can lead to considerable increase of database sizes in time.
   * Therefore it can be configured per repository.
   * <p>
   * <dt><b>Parallel Evolution</b>
   * <dd>Parallel evolution of the object graph stored in a repository through the concept of branches similar to source
   * code management systems like Subversion or Git. Comparisons or merges between any two branch points are supported
   * through sophisticated APIs, as well as the reconstruction of committed change sets or old states of single objects.
   * <p>
   * <dt><b>Scalability</b>
   * <dd>Scalability, the ability to store and access models of arbitrary size, is transparently achieved by loading
   * single objects on demand and caching them <i>softly</i> in your application. That implies that objects that are no
   * longer referenced by the application are automatically garbage collected when memory runs low. Lazy loading is
   * accompanied by various prefetching strategies, including the monitoring of the object graph's <i>usage</i> and the
   * calculation of fetch rules that are optimal for the current usage patterns. The scalability of EMF applications can
   * be further increased by leveraging CDO constructs such as remote cross referencing or optimized content adapters.
   * <p>
   * <dt><b>Thread Safety</b>
   * <dd>Thread safety ensures that multiple threads of your application can access and modify the object graph without
   * worrying about the synchronization details. This is possible and cheap because multiple transactions can be opened
   * from within a single session and they all share the same object data until one of them modifies the graph. Possible
   * commit conflicts can be handled in the same way as if they were conflicts between different sessions.
   * <p>
   * <dt><b>Collaboration</b>
   * <dd>Collaboration on models with CDO is a snap because an application can opt in to be notified about remote
   * changes to the object graph. By default your local object graph transparently changes when it has changed remotely.
   * With configurable change subscription policies you can fine tune the characteristics of your <i>distributed shared
   * model</i> so that all users enjoy the impression to collaborate on a single instance of an object graph. The level
   * of collaboration can be further increased by plugging custom collaboration handlers into the asynchronous CDO
   * protocol.
   * <p>
   * <dt><b>Data Integrity</b>
   * <dd>Data integrity can be ensured by enabling optional commit checks in the repository server such as referential
   * integrity checks and containment cycle checks, as well as custom checks implemented by write access handlers.
   * <p>
   * <dt><b>Security</b>
   * <dd>The data in a repository can be secured through pluggable {@link IAuthenticator authenticators} and
   * {@link IPermissionManager permission managers}. A default security model is provided on top of these low-level
   * components. The model comprises the concepts of users, groups, roles and extensible permissions.
   * <p>
   * <dt><b>Fault Tolerance</b>
   * <dd>Fault tolerance on multiple levels, namely the setup of fail-over clusters of replicating repositories under
   * the control of a fail-over monitor, as well as the usage of a number of special session types such as fail-over or
   * reconnecting sessions that allow applications to hold on their copy of the object graph even though the physical
   * repository connection has broken down or changed to a different fail-over participant.
   * <p>
   * <dt><b>Offline Work</b>
   * <dd>Offline work with your models is supported by two different mechanisms:
   * <ul>
   * <li>One way is to create a <b>clone</b> of a complete remote repository, including all history of all branches.
   * Such a clone is continuously synchronized with its remote master and can either act as an embedded repository to
   * make a single application tolerant against network outage or it can be set up to serve multiple clients, e.g., to
   * compensate low latency master connections and speed up read access to the object graph.
   * <p>
   * <li>An entirely different and somewhat lighter approach to offline work is to check out a single version of the
   * object graph from a particular branch point of the repository into a local CDO <b>workspace</b>. Such a workspace
   * behaves similar to a local repository without branching or history capture, in particular it supports multiple
   * concurrent transactions on the local checkout. In addition it supports most remote functionality that is known from
   * source code management systems such as update, merge, compare, revert and check in.
   * </ul>
   * </dl>
   */
  public class Functionality
  {
  }

  /**
   * Architecture
   * <p>
   * The architecture of CDO comprises applications and repositories. Despite a number of embedding options applications
   * are usually deployed to client nodes and repositories to server nodes. They communicate through an application
   * level CDO protocol which can be driven through various kinds of physical transports, including fast intra JVM
   * connections.
   * <p>
   * CDO has been designed to take full advantage of the OSGi platform, if available at runtime, but can perfectly be
   * operated in stand-alone deployments or in various kinds of containers such as JEE web or application servers.
   * <p>
   * The following chapters give an overview about the architectures of applications and repositories, respectively.
   */
  public class Architecture
  {
    /**
     * Client Architecture
     * <p>
     * {@link org.eclipse.emf.cdo.doc.programmers.client.Doc01_Architecture @inline}
     *
     * @see org.eclipse.emf.cdo.doc.programmers.client.Doc01_Architecture
     */
    public class Client
    {
    }

    /**
     * Repository Architecture
     * <p>
     * {@link org.eclipse.emf.cdo.doc.programmers.server.Architecture @inline}
     *
     * @see org.eclipse.emf.cdo.doc.programmers.server.Architecture
     */
    public class Repository
    {
    }
  }
}