--- a/doc/book/en/02-foundation.en.txt	Thu Nov 20 10:22:44 2008 -0800
+++ b/doc/book/en/02-foundation.en.txt	Thu Nov 20 10:25:44 2008 -0800
@@ -54,7 +54,7 @@
   stored in the database at the time an instance is created. `CubicWeb`
   provides a certain number of system entities included automatically as
   it is necessarry for the core of `CubicWeb` and a library of
-  cubes that can be explicitely included if necessarry.
+  cubes that can be explicitely included if necessary.
 
 
 *entity type*
@@ -76,6 +76,10 @@
   A relation is said final if its `object` is a final type. This is equivalent
   to an entity attribute.
 
+*relation definition*
+  a relation definition is a 3-uple (subject entity type, relation type, object entity type),
+  with an associated set of property such as cardinality, constraints...
+  
 *repository*
   This is the RQL server side of `CubicWeb`. Be carefull not to get
   confused with a Mercurial repository or a debian repository.
@@ -148,15 +152,15 @@
 
   
 .. _`Python Remote Object`: http://pyro.sourceforge.net/
-.. _`yams`: http://www.logilab.org/project/name/yams/
+.. _`yams`: http://www.logilab.org/project/yams/
 
 
 `CubicWeb` engine
 -----------------
 
-The web engine in `CubicWeb` is a set of classes managing a set of objects loaded
-dynamically at the startup of `CubicWeb`. Those dynamics objects, based on the schema
-or the library, are building the final web site. The differents dymanic components are
+The engine in `CubicWeb` is a set of classes managing a set of objects loaded
+dynamically at the startup of `CubicWeb` (*appobjects*). Those dynamics objects, based on the schema
+or the library, are building the final application. The differents dymanic components are
 by example:
 
 * client and server side
@@ -184,19 +188,144 @@
 
 * a frontal web (only twisted is available so far), transparent for dynamic objects
 * an object that encapsulates the configuration
-* a `vregistry` (`cubicweb.cwvreg`) containing the dynamic objects loaded automatically
+* a `registry` (`cubicweb.cwvreg`) containing the dynamic objects loaded automatically
 
+Every *appobject* may access to the instance configuration using its *config* attribute
+and to the registry using its *vreg* attribute.
 
-Details of a recording process
-------------------------------
+Details of the recording process
+--------------------------------
 
-At startup, the `vregistry` or registers base, inspects a number of directories
+At startup, the `registry` or registers base, inspects a number of directories
 looking for compatible classes definition. After a recording process, the objects
 are assigned to registers so that they can be selected dynamically while the
 application is running.
 
 The base class of those objects is `AppRsetObject` (module `cubicweb.common.appobject`).
 
+XXX registers example
+XXX actual details of the recording process!
+
+Runtime objects selection
+-------------------------
+XXX tell why it's a cw foundation!
+
+Application objects are stored in the registry using a two level hierarchy :
+
+  object's `__registry__` : object's `id` : [list of app objects]
+
+The following rules are applied to select an object given a register and an id and an input context:
+* each object has a selector
+  - its selector may be derivated from a set of basic (or not :)
+    selectors using `chainall` or `chainfirst` combinators
+* a selector return a score >= 0
+* a score of 0 means the objects can't be applied to the input context
+* the object with the greatest score is selected. If multiple objects have an
+  identical score, one of them is selected randomly (this is usually a bug)
+
+The object's selector is the `__selector__` class method on the object's class.
+
+The score is used to choose the most pertinent objects where there are more than
+one selectable object. For instance, if you're selecting the primary
+(eg `id = 'primary'`) view (eg `__registry__ = 'view'`) for a result set containing
+a `Card` entity, 2 objects will probably be selectable:
+
+* the default primary view (`accepts = 'Any'`)
+* the specific `Card` primary view (`accepts = 'Card'`)
+
+This is because primary views are using the `accept_selector` which is considering the
+`accepts` class attribute of the object's class. Other primary views specific to other
+entity types won't be selectable in this case. And among selectable objects, the
+accept selector will return a higher score the the second view since it's more
+specific, so it will be selected as expected.
+
+Usually, you won't define it directly but by defining the `__selectors__` tuple
+on the class, with ::
+
+  __selectors__ = (sel1, sel2)
+
+which is equivalent to ::
+
+  __selector__ = chainall(sel1, sel2)
+
+The former is prefered since it's shorter and it's ease overriding in
+subclasses (you have access to sub-selectors instead of the wrapping function).
+
+:chainall(selectors...): if one selector return 0, return 0, else return the sum of scores
+
+:chainfirst(selectors...): return the score of the first selector which has a non zero score
+
+XXX describe standard selector (link to generated api doc!)
+
+Example
+~~~~~~~
+Le but final : quand on est sur un Blog, on veut que le lien rss de celui-ci pointe
+vers les entrées de ce blog, non vers l'entité blog elle-même.
+
+L'idée générale pour résoudre ça : on définit une méthode sur les classes d'entité
+qui renvoie l'url du flux rss pour l'entité en question. Avec une implémentation
+par défaut sur AnyEntity et une implémentation particulière sur Blog qui fera ce
+qu'on veut.
+
+La limitation : on est embêté dans le cas ou par ex. on a un result set qui contient
+plusieurs entités Blog (ou autre chose), car on ne sait pas sur quelle entité appeler
+la méthode sus-citée. Dans ce cas, on va conserver le comportement actuel (eg appel
+à limited_rql)
+
+Donc : on veut deux cas ici, l'un pour un rset qui contient une et une seule entité,
+l'autre pour un rset qui contient plusieurs entité.
+
+Donc... On a déja dans web/views/boxes.py la classe RSSIconBox qui fonctionne. Son
+sélecteur ::
+
+  class RSSIconBox(ExtResourcesBoxTemplate):
+    """just display the RSS icon on uniform result set"""
+    __selectors__ = ExtResourcesBoxTemplate.__selectors__ + (nfentity_selector,)
+
+
+indique qu'il prend en compte :
+
+* les conditions d'apparition de la boite (faut remonter dans les classes parentes
+  pour voir le détail)
+* nfentity_selector, qui filtre sur des rset contenant une liste d'entité non finale
+
+ça correspond donc à notre 2eme cas. Reste à fournir un composant plus spécifique
+pour le 1er cas ::
+
+  class EntityRSSIconBox(RSSIconBox):
+    """just display the RSS icon on uniform result set for a single entity"""
+    __selectors__ = RSSIconBox.__selectors__ + (onelinerset_selector,)
+
+
+Ici, on ajoute onelinerset_selector, qui filtre sur des rset de taille 1. Il faut
+savoir que quand on chaine des selecteurs, le score final est la somme des scores
+renvoyés par chaque sélecteur (sauf si l'un renvoie zéro, auquel cas l'objet est
+non sélectionnable). Donc ici, sur un rset avec plusieurs entités, onelinerset_selector
+rendra la classe EntityRSSIconBox non sélectionnable, et on obtiendra bien la
+classe RSSIconBox. Pour un rset avec une entité, la classe EntityRSSIconBox aura un
+score supérieur à RSSIconBox et c'est donc bien elle qui sera sélectionnée.
+
+Voili voilou, il reste donc pour finir tout ça :
+
+* à définir le contenu de la méthode call de EntityRSSIconBox
+* fournir l'implémentation par défaut de la méthode renvoyant l'url du flux rss sur
+  AnyEntity
+* surcharger cette methode dans blog.Blog
+
+When to use selectors?
+~~~~~~~~~~~~~~~~~~~~~~
+Il faut utiliser les sélecteurs pour faire des choses différentes en
+fonction de ce qu'on a en entrée. Dès qu'on a un "if" qui teste la
+nature de `self.rset` dans un objet, il faut très sérieusement se
+poser la question s'il ne vaut pas mieux avoir deux objets différent
+avec des sélecteurs approprié.
+
+If this is so fundamental, why don't I see them more often?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Because you're usually using base classes which are hiding the plumbing
+of __registry__ (almost always), id (often when using "standard" object),
+register and selector.
+
 API Python/RQL
 --------------
 
@@ -435,3 +564,4 @@
 
 * the file ``__pkginfo__.py``
 * the schema definition
+  XXX false, we may want to have cubes which are only adding a service, no persistent data (eg embeding for instance)