Models in Grok, are classes which define the attributes and methods of objects identified at run time to serve as context for HTTP requests.   To properly understand the nature of models, one must realise that were one to declare:

class Article(grok.Model):
   implements(IArticle)
   title = u'My title'
   ...

...that the class definition only specifies what an Article instance should look like.  It's just a class (or type) declaration which implements something that looks like an IArticle.

At run time, while processing requests, we are dealing with instances of Article, which now provide an IArticle interface.  The Zope publisher is aware of the objects registered in the ZCA registry, and can process a URL to identify an object instance and a method (or view on the object).

The data associated with an Article instance may originate from a number of sources.  If the Article is derived from persistent.persistent, (for example, a grok.Model vs an object) then the Article instance may be stored in the ZoDB.  Alternately, the Article instance could represent a row in a relational database table, or the Article instance could be created dynamically (eg. myArticle=Article()). 

Dynamically created data models instances are called transient.  Such data lives only as long as the request does unless persisted in one or another database.

Finding Views

 If an Article instance was retrieved from the ZoDB, then it is most likely (but not always) retrieved as a result of the Zope publisher traversing the URL to locate the model.  At the same time, the publisher would identify a view, either by name from the URL, or use the default view named 'index'.  Views in Grok are also classes registered with the ZCA:

class Index(grok.View)
    grok.context(Article)
    ...

The view is registered with the ZCA object registry as an adapter by name ('index'), and having object interfaces (Article) and what the view is instantiated from (an IBrowserRequest).  So, when processing a Request, the Zope publisher can easily find the 'index' view for an IArticle and instantiate the view with an instance of Article as context.

Specifically, a view is looked up by the Zope publisher using a function

zope.component.getMultiAdapter((Article, Request), name='index')

The view is registered with the component registry when Grok parses the module and finds a declaration for the class Index(grok.View) with an appropriate context.