evolution/doc/Design

The Evolution Project specification
Miguel de Icaza.


* Introduction

	Evolution is a project aiming at providing the free software
	community with a professional, high-quality tool for managing
	mail, appointments, tasks and other personal information
	tools.  

	We want to make Evolution a system that addresses our needs
	(the free software development community) and we believe that
	by addressing our needs, we will provide a system that will
	scale in the years to come for other users that are just
	starting to use computers and the internet.

	The main objectives of Evolution are to provide these powerful
	features, and to make the user interface as pretty and
	polished as possible.

	Evolution is a GNOME application and a number of auxiliary
	CORBA servers that act as the storage backends. 

	Evolution will copy the best user interface bits and the best
	ideas and features found on contemporary groupware systems.

* Evolution internals.

	Evolution can store its information locally (files for mail,
	calendar and address book) or on a remote server (imap/pop,
	cap, ldap).  

	Given the importance of syncing in this modern PDA world,
	the Evolution GUI acts as a client to the data repository.
	The data repository is a GUI-less CORBA server called Wombat.

	Wombat provides a unified access system to the calendar and
	addressbook data (doing mail is a bit hard, so we are leaving
	this as a TODO item for now).

	Wombat's CORBA interfaces are notifier-based.  This means that
	CORBA requests sent to Wombat do not return values
	inmediately, but rather than for Wombat requests the user has
	to provide a CORBA object that will be notified of what
	happened.

	Yes, that sounds hairy.  It is actually pretty simple.  It
	basically means that you submit requests to Wombat, and a
	callback is invoked in your code when the request has been
	carried away. 

	This enables a Palm to sync to the repository without having
	the GUI for Evolution running.  It also means that volunteers
	will be able to write text-based and web-based versions of
	Evolution (not me though :-).

* Evolution as a platform

	Evolution is more than a client for managing the above
	information: Evolution is a platform for building groupware
	applications that use the above components to get their work done.

	To achieve this Evolution is designed to be scriptable, and it
	exports its internals trough CORBA/Bonobo.  It is implemented
	as a collection of Bonobo containers and Bonobo components.

	There is a clean separation between the views (the user
	interface) and the model (the view).  The views that we are
	writing are GNOME based, and they talk to the Wombat CORBA
	server.

	Wombat takes care of notifications to the various clients for
	the data. 

* The overall organization

	A bar similar to outlook provides shortcuts for accessing the
	various resources managed by Evolution: mail folders,
	contacts, tasks, journal entries, notes, messages and other
	user-defined destinations. 

* User interface widgets

** The ETable package

	This package provides a way of displaying and editing tables.

	Tables are displayed based on a TableColumn definition that
	defines the layout used for the display.  Table Columns can be
	nested, and the package does grouping of information displayed
	according to the criteria defined there.

	This is used in multiple places troughout evolution: it is
	used for the Mail summary display, for the TODO display and
	TODO new data entry and for the address book.

	Nesting in the address book can be performed on various
	fields.  For example, a first level of nesting could be
	"Company" and a second level would be "Country" the result is
	a 2-level tree that can be collapsed expanded and contains the
	information sorted/grouped by those two criteria.

	The user interface for this will be copied from Outlook: the
	possibility of adding and removing fields with drag and drop
	as well as grouping using drag and drop.

* The Mail system

** The Mail sources

	The mail system will support 4 sources of mail:

		POP3 (transfer to a local file).
		IMAP
		Local mbox format in $MAIL.
		Local mbox format that have other delivery points.

	On top of that, it will be possible to browse existing mbox
	archives (and possibly other formats in the future, like
	Mailbox and Maildir).

** Storing the mail

	Mail that gets incorporated into the system is stored in mbox
	format, and summary files are provided for quick access to the
	files.  No modifications to the file on disk is performed (I
	am not quite sure about this, perhaps we want to add the
	status flags and some method for adding metadata to the mail).

	Summary files are rebuilt on demand or rebuild if the mbox
	file and the summary file have got out of sync.

	A Metadata system that will enable us to attach information to
	a message will have to be designed and implemented (enabling
	users to add annotations to mails, and special keywords and
	flags in a per-message fashion).

** Folders

	Michael Zucchi is working on a system that will let users
	easily define rules for splitting their incoming mail into
	physical folders.  

	A further refinement to Folders are Virtual Folders.  This
	basically provides a powerful search and viewing facility for
	mail.  It works like this: when a mail is "incorporated" into
	Evolution it is scanned and indexed.

	Then users can enter queries into Evolution that will search
	the entire database of messages.	

** Virtual folders

	Virtual folders will enable users to read/browse their mail in
	new ways: by specifying search criterias, these folders will
	contain messages that match the criteria given.  

	There is more information about this in the libcamel
	directory. 

	We will index all headers from a message, and possible the
	contents of messages and keep those on a separate file, to
	enable users to query their mail database.

** Mail summary display

	The summary will be displayed using the ETable package, to
	enable users to add a number of sorting criteria and various
	display methods for the summary view.

	The Outlook methods for displaying will be present on the
	system.

	Message threading will be supported in Evolution.

** Message display engine

	We are going to be using a combination of
	libcamel/limime/libjamie to parse messages and render them
	into an HTML buffer.

* The HTML engine

	The GtkHTML engine will be used to display messages, and will
	be extended to support a number of features that we require:
	internal handling of characters will be based on Unicode

* The message composer

	Regular features found in composers will be added: connecting
	the composer to the address book, support for drag and drop
	for including attachments, editing the message, archiving
	drafts and archiving messages sent.

	Ettore has been working on adding editing support to the
	GtkHTML and he is working currently on a Bonobo component that
	will provide a ready-to-use Bonobo control for embedding into
	other applications.