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Glossary

.. glossary::
   :sorted:

   Template
      A snippet of ErlyDTL code which is used to render a piece of content (usually HTML). Templates live under the templates/ folder of a module. The template is meant to express presentation logic.

   Filter
      A template mechanism which is used inside a template to transform data before it is output. For instance: the .lower. filter transforms its input to lowercase. Filters are implemented as Erlang modules, exporting a single filter function.

   Action
      An action is functionality that can be attached to a HTML element or event. Actions are wired to an element or event. Think of showing dialogs, posting forms, hiding elements etc.

      See also :ref:`guide-actions` in the Developer Guide.

   Tag
      The template systems provides tags which function as simple programming constructs. For instance, the if tag can be used for boolean tests and the for tag allows looping. The Zotonic templating system compiles the tags found in a template to Erlang byte code which will be called when the template is rendered. This is very efficient.

   Scomp
      A scomp (from .Screen COMPonent.) is a custom template tag, implemented by an Erlang module named after the scomp name, prefixed with `scomp_`. Scomps usually generate HTML. Zotonic modules can implement their own scomp in the module.s scomps/ folder.

   Wire
      Connects actions and events to a HTML element. The wire scomp is the basis for most Ajax interaction on web pages. It allows to connected actions to HTML elements. Examples of actions are showing/hiding elements or postbacks to the server.
      ..todo:: hmm. It is scomp - it is also a often used function in the Erlang code z_render:wire/2

   Postback
      An AJAX or Websocket request from the browser to the server. It is handled on the server by event/2 Erlang functions. A postback is normally sent to the controller that generated the page, but can be changed by specifying a delegate, which must be the name of an Erlang module.

   Model
      An Erlang module which is the main accessor for retrieving data. The Erlang modules are prefixed with `m_`; in the templates they are accessible using .m... For instance, the model to access :term:`resources <resource>` is called ``m_rsc.erl``; in the template this model lets you access resources by id as ``{{ m.rsc[id] }}``.

   Service
      Also: API Service. Gives access to data or enables to call a function. The total set of API *calls* defines how an application responds to the outside world. Zotonic API Services provide a generalized way to create an API. API calls automatically use the authentication mechanism (session id or :ref:`OAuth <module-mod_oauth>`) to perform access checks. See :ref:`guide-services`.

   Validator
      A validator is used to check input fields in a HTML form. A validator has two parts: the client side javascript and a server side check. You add validators to a form with the {% validate %} template tag. A validated query argument can be accessed on the server using z_context:get_q_validated/2.

   Dispatch rule
      A dispatch rule maps URL patterns to controllers. Dispatch rules are defined in files in the .dispatch. folder of a Zotonic module. The dispatch rule definitions are also used to generate the urls for resources and other pages. See :ref:`guide-dispatch`.

   Controller
      A controller is the main entry point where a request is handled. Controllers are referenced from a dispatch rule. Commonly used controller is controller_template, which serves a template on the URL for which the controller configured. See :ref:`guide-controllers`.

   Context
      The context is the current request context. It contains all the request data, the current site, the handle to the database and the results (scripts or templates) you will be sending back. The context is commonly passed along in Zotonic as the last argument of a function.

   Session
      The session is an Erlang process. It is connected to the :term:`session cookie` id on the browser. The session contains the id of the current user and more key/value pairs, called session variables. The session is also linked to page processes. For every open page on the browser we have a process on the server. This page process is used for the communication between the server and the user-agent (browser).

   Session cookie
      A cookie is a small piece of data sent from a website and stored in a user’s web browser while the user is browsing that website. In contrast to perisistent cookies, session cookies are created and kept only during the user’s visit to the website, and deleted from the browser’s cache when the user closes the session.

   Category
      The data model has a hierarchical tree for the categorization of resources. Every resource is part of one category. The categorization is used amongst others to decide which template to show when displaying a resource. A category is a :term:`resource` of the category `category`. For more information, see :ref:`guide-datamodel-categories`.

   Page
      Another word for .resource.; used in the admin.

   Media
      Media are files, embed codes etc. They are attached to a resource. Every resource can hold a single medium. The resource is usually within the category `media`. See: :ref:`guide-media`.

   Page connection
      Another word for .edge.; used in the admin.

   Edge
      A :term:`resource` can connecto to other resources. These connections are called edges. Edges contain no information other than where they are linked to and from, and what their predicate is. Edges have a single direction, from the subject to the object.

   Predicate
      Each edge has a `label` attached to it to determine what the meaning of the edge is. For instance, when an article is linked to a person, the predicate (label) might read `author`, to indicate that that person is the author of the article. A predicate is a :term:`resource` of the category `predicate`.

   Property
      A field in a resource. Examples are title and summary. Properties are dynamically defined. Although some property names are reserved, you can set any other property, which will be stored in the resource.

   Data model
      :ref:`Zotonic’s generic data model <guide-datamodel>` of (categorized) resources which connect to other resources using labelled edges. This data model is loosely based on the principles of the semantic web.

   Domain model
      A particular configuration of resource categories and predicates, which dictate how resources of certain categories relate to each other. For example, a blog-type site might need `person`, `article` and `keyword` categories, where persons and articles are connected using the `author` predicate to indicate article authorship, and articles might be connected to keywords with `has_keyword` predicates. See :ref:`guide-datamodel`.

   Resource
      The main building block of the :ref:`data model <guide-datamodel>`. For simplicity of communication, a resource is often referred to as a page. Every resource usually has its own page on the web site. See :ref:`guide-datamodel-resources`.

   Translation
      There are two kinds of translations. Texts in the templates and Erlang modules; and translations of resources. Templates and Erlang modules are translated using gettext. Resources are translated in the admin, any resource can have an arbitrary number of translations. Zotonic selects the shown language based on the preferred language of the visitor and the available languages of a resource.

   Zotonic module
      A Zotonic module (just .module., for short) is a collection of related functionality like scomps, filters, dispatch rules, controllers, templates, etc. Zotonic modules are located in folders under the modules/ directory and, by convention, are prefixed with `mod_`. See :ref:`guide-modules`.

   Zotonic site
      A Zotonic site is a collection of scomps, filters, dispatch rules for one website. It is a special kind of Zotonic module with has its own config file which allows one to set the hostname, admin password, database connection parameters. It often has a set of site specific modules. The config file contains site wide settings. Zotonic uses the settings to start the site on the right port and connect it to the right database. A Zotonic system can run multiple sites.

   Erlang module
      Not to be confused with a Zotonic module, an Erlang module is a single .erl file which contains Erlang functions.

   Non Informational URI
      The non informational uri is the base url of a resource. It always redirects to a representation of the resource. Think of a HTML page, image or JSON download. The chosen representation depends on the .Accept. HTTP request header. The non informational uri of a resource is always like http://example.com/id/1234

   Comet
       Comet is a web application model in which a long-held HTTP request allows a web server to push data to a browser, without the browser explicitly requesting it (source: `Wikipedia <http://en.wikipedia.org/wiki/Comet_(programming)>`_).

   Delegate
        A reference to a module which will be used to call a callback function on. Used in the templates when attaching actions like a :term:postback to a DOM Event. See :ref:`guide-actions`.

   User sites directory
        The directory in which user-installed Zotonic sites are placed. Defaults to the path ``user/sites`` relative to the Zotonic installation, but can be adjusted by changing the ``user_sites_dir`` configuration variable in the global ``zotonic.config`` file. See :ref:`guide-configuration`.

   User modules directory
        The directory in which user-installed Zotonic modules are placed. Defaults to the path ``user/modules`` relative to the Zotonic installation, but can be adjusted by changing the ``user_modules_dir`` configuration variable in the global ``zotonic.config`` file. See :ref:`guide-configuration`.