Open Graph Web Protocol
Open Graph protocol

Introduction
The Open Graph protocol enables any web page to become a
rich object in a social graph. For instance, this is used on Facebook to allow
any web page to have the same functionality as any other object on Facebook.
While many different technologies and schemas exist and could be combined
together, there isn't a single technology which provides enough information to
richly represent any web page within the social graph. The Open Graph protocol
builds on these existing technologies and gives developers one thing to
implement. Developer simplicity is a key goal of the Open Graph protocol which
has informed many of the technical design decisions.



To turn your web pages into graph objects, you need to add basic metadata to
your page. We've based the initial version of the protocol on
RDFa which means that you'll place
additional <meta> tags in the <head> of your web page. The four required
properties for every page are:

og:title - The title of your object as it should appear within the graph,
e.g., "The Rock".
og:type - The type of your object, e.g., "video.movie".  Depending on
the type you specify, other properties may also be required.
og:image - An image URL which should represent your object within the
graph.
og:url - The canonical URL of your object that will be used as its
permanent ID in the graph, e.g., "https://www.imdb.com/title/tt0117500/".

As an example, the following is the Open Graph protocol markup for The Rock on
IMDB:
<html prefix="og: https://ogp.me/ns#">
<head>
<title>The Rock (1996)</title>
<meta property="og:title" content="The Rock" />
<meta property="og:type" content="video.movie" />
<meta property="og:url" content="https://www.imdb.com/title/tt0117500/" />
<meta property="og:image" content="https://ia.media-imdb.com/images/rock.jpg" />
...
</head>
...
</html>

Optional Metadata
The following properties are optional for any object and are generally
recommended:

og:audio - A URL to an audio file to accompany this object.
og:description - A one to two sentence description of your object.
og:determiner - The word that appears before this object's title
in a sentence. An enum of (a, an, the, "", auto). If auto is 
chosen, the consumer of your data should chose between "a" or "an".
Default is "" (blank).
og:locale - The locale these tags are marked up in.
Of the format language_TERRITORY. Default is en_US.
og:locale:alternate - An array of other locales this page is 
available in.
og:site_name - If your object is part of a larger web site, the name which
should be displayed for the overall site. e.g., "IMDb".
og:video - A URL to a video file that complements this object.

For example (line-break solely for display purposes):
<meta property="og:audio" content="https://example.com/bond/theme.mp3" />
<meta property="og:description" 
  content="Sean Connery found fame and fortune as the
           suave, sophisticated British agent, James Bond." />
<meta property="og:determiner" content="the" />
<meta property="og:locale" content="en_GB" />
<meta property="og:locale:alternate" content="fr_FR" />
<meta property="og:locale:alternate" content="es_ES" />
<meta property="og:site_name" content="IMDb" />
<meta property="og:video" content="https://example.com/bond/trailer.swf" />

The RDF schema (in Turtle) 
can be found at ogp.me/ns.

Structured Properties
Some properties can have extra metadata attached to them.
These are specified in the same way as other metadata with property and
content, but the property will have extra :.
The og:image property has some optional structured properties:

og:image:url - Identical to og:image.
og:image:secure_url - An alternate url to use if the webpage requires
HTTPS.
og:image:type - A MIME type for this image.
og:image:width - The number of pixels wide.
og:image:height - The number of pixels high.
og:image:alt - A description of what is in the image (not a caption). If the page specifies an og:image it should specify og:image:alt.

A full image example:
<meta property="og:image" content="https://example.com/ogp.jpg" />
<meta property="og:image:secure_url" content="https://secure.example.com/ogp.jpg" />
<meta property="og:image:type" content="image/jpeg" />
<meta property="og:image:width" content="400" />
<meta property="og:image:height" content="300" />
<meta property="og:image:alt" content="A shiny red apple with a bite taken out" />

The og:video tag has the identical tags as og:image. Here is an example:
<meta property="og:video" content="https://example.com/movie.swf" />
<meta property="og:video:secure_url" content="https://secure.example.com/movie.swf" />
<meta property="og:video:type" content="application/x-shockwave-flash" />
<meta property="og:video:width" content="400" />
<meta property="og:video:height" content="300" />

The og:audio tag only has the first 3 properties available
(since size doesn't make sense for sound):
<meta property="og:audio" content="https://example.com/sound.mp3" />
<meta property="og:audio:secure_url" content="https://secure.example.com/sound.mp3" />
<meta property="og:audio:type" content="audio/mpeg" />


Arrays
If a tag can have multiple values, just put multiple versions of the same
<meta> tag on your page. The first tag (from top to bottom) is given
preference during conflicts.
<meta property="og:image" content="https://example.com/rock.jpg" />
<meta property="og:image" content="https://example.com/rock2.jpg" />

Put structured properties after you declare their root tag. Whenever
another root element is parsed, that structured property
is considered to be done and another one is started.
For example:
<meta property="og:image" content="https://example.com/rock.jpg" />
<meta property="og:image:width" content="300" />
<meta property="og:image:height" content="300" />
<meta property="og:image" content="https://example.com/rock2.jpg" />
<meta property="og:image" content="https://example.com/rock3.jpg" />
<meta property="og:image:height" content="1000" />

means there are 3 images on this page, the first image is 300x300, the middle
one has unspecified dimensions, and the last one is 1000px tall.

Object Types
In order for your object to be represented within the graph, you need to
specify its type. This is done using the og:type property:
<meta property="og:type" content="website" />

When the community agrees on the schema for a type, it is added to the list
of global types. All other objects in the type system are
CURIEs of the form
<head prefix="my_namespace: https://example.com/ns#">
<meta property="og:type" content="my_namespace:my_type" />

The global types are grouped into verticals. Each vertical has its
own namespace. The og:type values for a namespace are always prefixed with
the namespace and then a period.
This is to reduce confusion with user-defined namespaced types which always
have colons in them.
Music

Namespace URI: https://ogp.me/ns/music#

og:type values:
music.song

music:duration - integer >=1 - The song's length in seconds.
music:album - music.album array -
The album this song is from.
music:album:disc - integer >=1 -
Which disc of the album this song is on.
music:album:track - integer >=1 -
Which track this song is.
music:musician - profile array -
The musician that made this song.

music.album

music:song - music.song - The song on this album.
music:song:disc - integer >=1 -
The same as music:album:disc but in reverse.
music:song:track - integer >=1 -
The same as music:album:track but in reverse.
music:musician - profile -
The musician that made this song.
music:release_date - datetime - 
The date the album was released.

music.playlist

music:song - Identical to the ones on music.album
music:song:disc
music:song:track
music:creator - profile - The creator of this playlist.

music.radio_station

music:creator - profile - The creator of this station.

Video

Namespace URI: https://ogp.me/ns/video#

og:type values:
video.movie

video:actor - profile array -
Actors in the movie.
video:actor:role - string - The role they played.
video:director - profile array -
Directors of the movie.
video:writer - profile array -
Writers of the movie.
video:duration - integer >=1 - 
The movie's length in seconds.
video:release_date - datetime - 
The date the movie was released.
video:tag - string array -
Tag words associated with this movie.

video.episode

video:actor - Identical to video.movie
video:actor:role
video:director
video:writer
video:duration
video:release_date
video:tag
video:series - video.tv_show -
Which series this episode belongs to.

video.tv_show
A multi-episode TV show.
The metadata is identical to video.movie.
video.other
A video that doesn't belong in any other category.
The metadata is identical to video.movie.
No Vertical
These are globally defined objects that just don't fit into a vertical but
yet are broadly used and agreed upon.
og:type values:
article - Namespace URI: https://ogp.me/ns/article#

article:published_time - datetime - 
When the article was first published.
article:modified_time - datetime - 
When the article was last changed.
article:expiration_time - datetime - 
When the article is out of date after.
article:author - profile array -
Writers of the article.
article:section - string - A high-level section name. E.g. Technology
article:tag - string array -
Tag words associated with this article.

book - Namespace URI: https://ogp.me/ns/book#

book:author - profile array - Who wrote this book.
book:isbn - string -
The ISBN
book:release_date - datetime - The date the book was released.
book:tag - string array -
Tag words associated with this book.

profile - Namespace URI: https://ogp.me/ns/profile#

profile:first_name - string - A name normally given to an individual by a parent or self-chosen.
profile:last_name - string - A name inherited from a family or marriage and by which the individual is commonly known.
profile:username - string - A short unique string to identify them.
profile:gender - enum(male, female) - Their gender.

website - Namespace URI: https://ogp.me/ns/website#
No additional properties other than the basic ones.
Any non-marked up webpage should be treated as og:type website.

Types
The following types are used when defining attributes in Open Graph protocol.


  Type
  Description
  Literals



  Boolean
  A Boolean represents a true or false value
  true, false, 1, 0



  DateTime
  A DateTime represents a temporal value composed of a date
    (year, month, day) and an optional time component (hours, minutes)
  ISO 8601



  Enum
  A type consisting of bounded set of constant string values 
  (enumeration members).
  A string value that is a member of the enumeration



  Float
  A 64-bit signed floating point number
  All literals that conform to the following formats:
1.234
-1.234
1.2e3
-1.2e3
7E-10



  Integer
  A 32-bit signed integer. In many languages integers over 32-bits become 
    floats, so we limit Open Graph protocol for easy multi-language use.
  All literals that conform to the following formats:
1234
-123



  String
  A sequence of Unicode characters
  All literals composed of Unicode characters with no escape characters



  URL
  A sequence of Unicode characters that identify an Internet resource.
  All valid URLs that utilize the https:// or https:// protocols




Discussion and support
You can discuss the Open Graph Protocol in
the Facebook group or on 
the developer mailing list.
It is currently being consumed by Facebook (see their documentation), 
Google (see their documentation), and
mixi.
It is being published by IMDb, Microsoft, NHL, Posterous, Rotten Tomatoes,
TIME, Yelp, and many many others.

Implementations
The open source community has developed a number of parsers and publishing
tools. Let the Facebook group know if you've built something awesome too!

Facebook Object Debugger -
Facebook's official parser and debugger
Google Rich Snippets Testing Tool - Open Graph protocol support in specific verticals and Search Engines.
PHP Validator and Markup Generator -  OGP 2011 input validator and markup generator in PHP5 objects
PHP Consumer -
a small library for accessing of Open Graph Protocol data in PHP
OpenGraphNode in PHP -
a simple parser for PHP
PyOpenGraph -
a library written in Python for parsing Open Graph protocol
information from web sites
OpenGraph Ruby -
Ruby Gem which parses web pages and extracts Open Graph protocol markup
OpenGraph for Java -
small Java class used to represent the Open Graph protocol
RDF::RDFa::Parser -
Perl RDFa parser which understands the Open Graph protocol
WordPress plugin -
Facebook's official WordPress plugin, which adds Open Graph metadata to WordPress powered sites. 
Alternate WordPress OGP plugin -
A simple lightweight WordPress plugin which adds Open Graph metadata to WordPress powered sites. 

    