json-activity.xml

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<rfc>
  <front>
    <title abbrev="ActivityStreams">JSON Activity Streams 1.0</title>

    <author fullname="James M Snell" initials="J.M." surname="Snell">
      <organization>IBM</organization>
    </author>

    <author fullname="Martin Atkins" initials="M." surname="Atkins">
      <organization>SAY Media</organization>
    </author>

    <author fullname="Will Norris" initials="W." surname="Norris">
      <organization>Google</organization>
    </author>

    <author fullname="Chris Messina" initials="C." surname="Messina">
      <organization>Citizen Agency, Google</organization>
    </author>

    <author fullname="Monica Wilkinson" initials="M." surname="Wilkinson">
      <organization>MySpace, Facebook, VMware</organization>
    </author>

    <author fullname="Rob Dolin" initials="R." surname="Dolin">
      <organization>Microsoft</organization>
    </author>

    <date month="May" year="2011" />

    <abstract>
      <t>This specification details the serialization of a stream of social
        activities using the JSON format. Activities are important in that
        they allow individuals to process the latest news of people and things
        they care about.</t>
    </abstract>

  </front>

  <middle>
    <section anchor="introduction" title="Introduction">

      <t>In its simplest form, an <spanx style="verb">activity</spanx> consists
      of an <spanx style="verb">actor</spanx>, a
      <spanx style="verb">verb</spanx>, an
      an <spanx style="verb">object</spanx>, and a <spanx style="verb">target</spanx>.
      It tells the story of a person performing an action on or with an object --
      "Geraldine posted a photo to her album"
      or "John shared a video". In most cases these components will be
      explicit, but they may also be implied.</t>

      <t>It is a goal of this specification to provide sufficient metadata
      about an activity such that a consumer of the data can present it to a
      user in a rich human-friendly format. This may include constructing
      readable sentences about the activity that occurred, visual
      representations of the activity, or combining similar activities for
      display.</t>

      <t>The basic properties that comprise the description of an
      <spanx style="verb">activity</spanx> are defined in the following sections.</t>

      <t>Within this specification, an <spanx style="verb">object</spanx> is a
      thing, real or imaginary, which participates in an
      activity. It may be the entity performing the activity, or the entity
      on which the activity was performed. An <spanx style="verb">object</spanx>
      consists of properties defined in the following sections. Certain object
      types may further refine the meaning of these properties, or they may
      define additional properties.</t>

      <t>Some types of objects may have an alternative visual representation
      in the form of an image, video or embedded HTML fragments.
      A <spanx style="verb">Media Link</spanx> represents a hyperlink to
      such resources.</t>

      <t>An <spanx style="verb">Activity Stream</spanx> is a collection one or
      more individual activities. The relationship between the activities within
      the collection is undefined by this specification.</t>

    </section>

    <section anchor="notation" title="Notational Conventions">
      <t>The text of this specification provides the sole definition of
      conformance. Examples in this specification are non-normative.</t>

      <t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
      "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
      document are to be interpreted as described in <xref
      target="RFC2119" />.</t>

      <t>This specification allows the use of IRIs <xref target="RFC3987"/>.
      Every URI <xref target="RFC3986" /> is also an IRI, so a URI may be used
      wherever below an IRI is named.  There are two special considerations:
      (1) when an IRI that is not also a URI is given for dereferencing, it
      MUST be mapped to a URI using the steps in Section 3.1 of
      <xref target="RFC3987"/> and (2) when an IRI is serving as
      an <spanx style="verb">id</spanx> value, it MUST NOT be so mapped.</t>
    </section>

    <section anchor="json" title="JSON Serialization">

      <t>Activities are serialized using the JSON format, as
      defined in <xref target="RFC4627" />. Alternative serializations
      MAY be used but are outside the scope of this specification.</t>

      <t>In the JSON serialization, absent properties MAY be represented either
      by an explicit declaration of the property whose value is null or by
      omitting the property declaration altogether at the option of the
      publisher; these two representations are semantically equivalent. If a
      property is having a value whose type is a JSON array, the absence of
      any items in that array MUST be represented by omitting the property
      entirely or publishing it with the value null, and MUST NOT be
      represented as an empty array, except as otherwise stated in the
      definition of a specific property.</t>

      <t>Unless otherwise specified, all properties specifying date and
      time values within the JSON serialization, including extensions,
      MUST conform to the "date-time" production in <xref target="RFC3339" />.
      In addition, an uppercase "T" character MUST be used to separate date
      and time, and an uppercase "Z" character MUST be present in the absence of
      a numeric time zone offset.</t>

      <section anchor="examples" title="Example Activities">

        <t>Following is a simple, minimal example of a JSON serialized
        <spanx style="verb">activity</spanx>:</t>

<figure><artwork><![CDATA[
  {
    "published": "2011-02-10T15:04:55Z",
    "actor": {
      "url": "http://example.org/martin",
      "objectType" : "person",
      "id": "tag:example.org,2011:martin",
      "image": {
        "url": "http://example.org/martin/image",
        "width": 250,
        "height": 250
      },
      "displayName": "Martin Smith"
    },
    "verb": "post",
    "object" : {
      "url": "http://example.org/blog/2011/02/entry",
      "id": "tag:example.org,2011:abc123/xyz"
    },
    "target" : {
      "url": "http://example.org/blog/",
      "objectType": "blog",
      "id": "tag:example.org,2011:abc123",
      "displayName": "Martin's Blog"
    }
  }
]]></artwork></figure>

        <t>A more extensive, single-entry <spanx style="verb">Activity Stream</spanx>
        follows. In addition to containing a number of required and optional
        core properties, the example contains the additional, undefined extension
        properties "foo" and "foo2" for illustrative purposes only.</t>

<figure><artwork><![CDATA[
  {
    "items" : [
      {
        "published": "2011-02-10T15:04:55Z",
        "foo": "some extension property",
        "generator": {
          "url": "http://example.org/activities-app"
        },
        "provider": {
          "url": "http://example.org/activity-stream"
        },
        "title": "Martin posted a new video to his album.",
        "actor": {
          "url": "http://example.org/martin",
          "objectType": "person",
          "id": "tag:example.org,2011:martin",
          "foo2": "some other extension property",
          "image": {
            "url": "http://example.org/martin/image",
            "width": 250,
            "height": 250
          },
          "displayName": "Martin Smith"
        },
        "verb": "post",
        "object" : {
          "url": "http://example.org/album/my_fluffy_cat.jpg",
          "objectType": "photo",
          "id": "tag:example.org,2011:my_fluffy_cat",
          "image": {
            "url": "http://example.org/album/my_fluffy_cat_thumb.jpg",
            "width": 250,
            "height": 250
          }
        },
        "target": {
          "url": "http://example.org/album/",
          "objectType": "photo-album",
          "id": "tag:example.org,2011:abc123",
          "displayName": "Martin's Photo Album",
          "image": {
            "url": "http://example.org/album/thumbnail.jpg",
            "width": 250,
            "height": 250
          }
        }
      }
    ]
  }
]]></artwork></figure>

      </section>

      <section anchor="activity" title="Activity Serialization">

        <texttable>
          <ttcol align="left" width="15%">Property</ttcol>
          <ttcol align="left" width="21%">Value</ttcol>
          <ttcol align="left">Description</ttcol>

          <c><spanx style="verb">actor</spanx></c>
          <c><xref target="object">Object</xref></c>
          <c>Describes the entity that performed the activity. An activity
          MUST contain one <spanx style="verb">actor</spanx> property whose value is a
          single <xref target="object">Object</xref>.</c>

          <c><spanx style="verb">content</spanx></c>
          <c><xref target="RFC4627">JSON</xref> String</c>
          <c>Natural-language description of the activity encoded as a single
          JSON String containing HTML markup. Visual elements such as thumbnail
          images MAY be included. An activity MAY contain a
          <spanx style="verb">content</spanx> property.</c>

          <c><spanx style="verb">generator</spanx></c>
          <c><xref target="object">Object</xref></c>
          <c>Describes the application that generated the activity. An activity
          MAY contain a <spanx style="verb">generator</spanx> property whose value is a single
          <xref target="object">Object</xref>.</c>

          <c><spanx style="verb">icon</spanx></c>
          <c><xref target="media-link">Media Link</xref></c>
          <c>Description of a resource providing a visual representation of
          the object, intended for human consumption. The image SHOULD have an
          aspect ratio of one (horizontal) to one (vertical) and SHOULD be suitable
          for presentation at a small size. An activity MAY have an
          <spanx style="verb">icon</spanx> property.</c>

          <c><spanx style="verb">id</spanx></c>
          <c><xref target="RFC4627">JSON</xref> String</c>
          <c>Provides a permanent, universally unique identifier for the
          activity in the form of an absolute IRI <xref target="RFC3987"/>.
          An activity SHOULD contain a single <spanx style="verb">id</spanx> property. If an activity
          does not contain an <spanx style="verb">id</spanx> property, consumers MAY use the value of
          the <spanx style="verb">url</spanx> property as a less-reliable, non-unique identifier.</c>

          <c><spanx style="verb">object</spanx></c>
          <c><xref target="object">Object</xref></c>
          <c>Describes the primary object of the activity. For instance,
          in the activity, "John saved a movie to his wishlist", the object
          of the activity is "movie". An activity SHOULD contain an
          <spanx style="verb">object</spanx> property whose value is a single
          <xref target="object">Object</xref>. If the
          <spanx style="verb">object</spanx> property is not contained, the
          primary object of the activity MAY be implied by context.</c>

          <c><spanx style="verb">published</spanx></c>
          <c><xref target="RFC3339"/> date-time</c>
          <c>The date and time at which the activity was published. An activity
          MUST contain a <spanx style="verb">published</spanx> property.</c>

          <c><spanx style="verb">provider</spanx></c>
          <c><xref target="object">Object</xref></c>
          <c>Describes the application that published the activity. Note that
          this is not necessarily the same entity that generated the activity.
          An activity MAY contain a <spanx style="verb">provider</spanx> property whose value is a
          single <xref target="object">Object</xref>.</c>

          <c><spanx style="verb">target</spanx></c>
          <c><xref target="object">Object</xref></c>
          <c>Describes the target of the activity. The precise meaning of the
          activity's target is dependent on the activities <spanx style="verb">verb</spanx>,
          but will often be the object the English preposition "to".
          For instance, in the activity, "John saved a movie to his
          wishlist", the target of the activity is "wishlist". The activity
          target MUST NOT be used to identity an indirect object that is
          not a target of the activity. An activity MAY contain a <spanx style="verb">target</spanx>
          property whose value is a single <xref target="object">Object</xref>.</c>

          <c><spanx style="verb">title</spanx></c>
          <c><xref target="RFC4627">JSON</xref> String</c>
          <c>Natural-language title or headline for the activity encoded as a single
          JSON String containing HTML markup. An activity MAY contain a
          <spanx style="verb">title</spanx> property.</c>

          <c><spanx style="verb">updated</spanx></c>
          <c><xref target="RFC3339"/> date-time</c>
          <c>The date and time at which a previously published activity has
          been modified. An Activity MAY contain an <spanx style="verb">updated</spanx>
          property.</c>

          <c><spanx style="verb">url</spanx></c>
          <c><xref target="RFC4627">JSON</xref> String</c>
          <c>An IRI <xref target="RFC3987"/> identifying a resource providing
          an HTML representation of the activity. An activity MAY contain
          a <spanx style="verb">url</spanx> property.</c>

          <c><spanx style="verb">verb</spanx></c>
          <c><xref target="RFC4627">JSON</xref> String</c>
          <c>Identifies the action that the activity describes. An activity
          SHOULD contain a <spanx style="verb">verb</spanx> property whose
          value is a JSON String that is non-empty and matches either the
          "isegment-nz-nc" or the "IRI" production in <xref target="RFC3339"/>.
          Note that the use of a relative reference other than a simple name
          is not allowed. If the <spanx style="verb">verb</spanx> is not
          specified, or if the value is null, the <spanx style="verb">verb</spanx>
          is assumed to be <xref target="post-verb">"post"</xref>.</c>

        </texttable>
      </section>

      <section anchor="media-link" title="Media Link Serialization">

        <texttable>
          <ttcol align="left" width="15%">Property</ttcol>
          <ttcol align="left" width="21%">Value</ttcol>
          <ttcol align="left">Description</ttcol>

          <c><spanx style="verb">duration</spanx></c>
          <c><xref target="RFC4627">JSON</xref> int</c>
          <c>A hint to the consumer about the length, in seconds, of the
          media resource identified by the <spanx style="verb">url</spanx> property. A media link MAY
          contain a "duration" property when the target resource is a
          time-based media item such as an audio or video.</c>

          <c><spanx style="verb">height</spanx></c>
          <c><xref target="RFC4627">JSON</xref> int</c>
          <c>A hint to the consumer about the height, in pixels, of the
          media resource identified by the <spanx style="verb">url</spanx> property. A media link MAY
          contain a <spanx style="verb">height</spanx> property when the target resource is a visual
          media item such as an image, video or embeddable HTML page.</c>

          <c><spanx style="verb">url</spanx></c>
          <c>String</c>
          <c>The IRI of the media resource being linked. A media link MUST
          have a <spanx style="verb">url</spanx> property.</c>

          <c><spanx style="verb">width</spanx></c>
          <c><xref target="RFC4627">JSON</xref> int</c>
          <c>A hint to the consumer about the width, in pixels, of the
          media resource identified by the <spanx style="verb">url</spanx> property. A media link MAY
          contain a <spanx style="verb">width</spanx> property when the target resource is a visual
          media item such as an image, video or embeddable HTML page.</c>

        </texttable>

      </section>

      <section anchor="object" title="Object Serialization">

        <texttable>
          <ttcol align="left" width="15%">Property</ttcol>
          <ttcol align="left" width="21%">Value</ttcol>
          <ttcol align="left">Description</ttcol>

          <c><spanx style="verb">attachments</spanx></c>
          <c><xref target="RFC4627">JSON</xref> Array of <xref target="object">Objects</xref></c>
          <c>A collection of one or more additional, associated objects, similar
          to the concept of attached files in an email message. An object MAY
          have an <spanx style="verb">attachments</spanx> property whose value is a JSON Array of
          <xref target="object">Objects</xref>.</c>

          <c><spanx style="verb">author</spanx></c>
          <c><xref target="object">Object</xref></c>
          <c>Describes the entity that created or authored the object. An
          object MAY contain a single <spanx style="verb">author</spanx>
          property whose value is an <xref target="object">Object</xref>
          of any type. Note that the author field identifies the entity that
          created the object and does not necessarily identify the entity
          that published the object. For instance, it may be the case that
          an object created by one person is posted and published to a system
          by an entirely different entity.</c>

          <c><spanx style="verb">content</spanx></c>
          <c><xref target="RFC4627">JSON</xref> String</c>
          <c>Natural-language description of the object encoded as a single
          JSON String containing HTML markup. Visual elements such as thumbnail
          images MAY be included. An object MAY contain a
          <spanx style="verb">content</spanx> property.</c>

          <c><spanx style="verb">displayName</spanx></c>
          <c><xref target="RFC4627">JSON</xref> String</c>
          <c>A natural-language, human-readable and plain-text name for the object.
          HTML markup MUST NOT be included. An object MAY contain a <spanx style="verb">displayName</spanx>
          property. If the object does not specify an <spanx style="verb">objectType</spanx>
          property, the object SHOULD specify a <spanx style="verb">displayName</spanx>.</c>

          <c><spanx style="verb">downstreamDuplicates</spanx></c>
          <c><xref target="RFC4627">JSON</xref> Array of Strings</c>
          <c>A JSON Array of one or more absolute IRI's <xref target="RFC3987"/>
          identifying objects that duplicate this object's content. An object
          SHOULD contain a <spanx style="verb">downstreamDuplicates</spanx> property when there are known
          objects, possibly in a different system, that duplicate the content
          in this object. This MAY be used as a hint for consumers to use when
          resolving duplicates between objects received from different sources.</c>

          <c><spanx style="verb">id</spanx></c>
          <c><xref target="RFC4627">JSON</xref> String</c>
          <c>Provides a permanent, universally unique identifier for the
          object in the form of an absolute IRI <xref target="RFC3987"/>.
          An object SHOULD contain a single <spanx style="verb">id</spanx> property. If an object
          does not contain an <spanx style="verb">id</spanx> property, consumers MAY use the value of
          the <spanx style="verb">url</spanx> property as a less-reliable, non-unique identifier.</c>

          <c><spanx style="verb">image</spanx></c>
          <c><xref target="media-link">Media Link</xref></c>
          <c>Description of a resource providing a visual representation of
          the object, intended for human consumption. An object MAY contain
          an <spanx style="verb">image</spanx> property whose value is a
          <xref target="media-link">Media Link</xref>.</c>

          <c><spanx style="verb">objectType</spanx></c>
          <c><xref target="RFC4627">JSON</xref> String</c>
          <c>Identifies the type of object. An object MAY contain an
          <spanx style="verb">objectType</spanx>
          property whose value is a JSON String that is non-empty and matches
          either the "isegment-nz-nc" or the "IRI" production in
          <xref target="RFC3987"/>. Note that the use of a relative reference
          other than a simple name is not allowed. If no
          <spanx style="verb">objectType</spanx> property
          is contained, the object has no specific type.</c>

          <c><spanx style="verb">published</spanx></c>
          <c><xref target="RFC3339"/> date-time</c>
          <c>The date and time at which the object was published. An object
          MAY contain a <spanx style="verb">published</spanx> property.</c>

          <c><spanx style="verb">summary</spanx></c>
          <c><xref target="RFC4627">JSON</xref> String</c>
          <c>Natural-language summarization of the object encoded as a single
          JSON String containing HTML markup. Visual elements such as thumbnail
          images MAY be included. An activity MAY contain a
          <spanx style="verb">summary</spanx> property.</c>

          <c><spanx style="verb">updated</spanx></c>
          <c><xref target="RFC3339"/> date-time</c>
          <c>The date and time at which a previously published object has
          been modified. An Object MAY contain an <spanx style="verb">updated</spanx>
          property.</c>

          <c><spanx style="verb">upstreamDuplicates</spanx></c>
          <c><xref target="RFC4627">JSON</xref> Array of Strings</c>
          <c>A JSON Array of one or more absolute IRI's <xref target="RFC3987"/>
          identifying objects that duplicate this object's content.
          An object SHOULD contain an <spanx style="verb">upstreamDuplicates</spanx>
          property when a publisher is knowingly duplicating with a new ID
          the content from another object. This MAY be used as a hint for consumers to use
          when resolving duplicates between objects received from different
          sources.</c>

          <c><spanx style="verb">url</spanx></c>
          <c><xref target="RFC4627">JSON</xref> String</c>
          <c>An IRI <xref target="RFC3987"/> identifying a resource providing
          an HTML representation of the object. An object MAY contain
          a <spanx style="verb">url</spanx> property </c>

        </texttable>
      </section>

      <section anchor="collection" title="Collection Serialization">

        <t>A "collection" is a generic list of <xref target="object">Objects</xref>
        of any object type. The <spanx style="verb">objectType</spanx> of each
        item in the collection MAY be omitted if the type of object can be established
        through context. The collection is used primarily as the root of an
        Activity Streams document as described in <xref target="document"/>,
        but can be used as the value of extension properties in a variety
        of situations.</t>

        <texttable>
          <ttcol align="left" width="15%">Property</ttcol>
          <ttcol align="left" width="21%">Value</ttcol>
          <ttcol align="left">Description</ttcol>

          <c><spanx style="verb">totalItems</spanx></c>
          <c><xref target="RFC4627">JSON</xref> Integer</c>
          <c>Non-negative integer specifying the total number of activities
          within the stream. The Stream serialization MAY contain a
          <spanx style="verb">count</spanx> property.</c>

          <c><spanx style="verb">items</spanx></c>
          <c><xref target="RFC4627">JSON</xref> Array of
          <xref target="object">Objects</xref></c>
          <c>An array containing a listing of
          <xref target="object">Objects</xref> of any
          object type. If used in combination with the <spanx style="verb">url</spanx>
          property, the <spanx style="verb">items</spanx> array can be used
          to provide a subset of the objects that may be found in the resource
          identified by the <spanx style="verb">url</spanx>.</c>

          <c><spanx style="verb">url</spanx></c>
          <c><xref target="RFC4627">JSON</xref> String</c>
          <c>An IRI <xref target="RFC3987"/> referencing a
          JSON document containing the full listing of objects in the
          collection.</c>

        </texttable>

        <t>A valid Collection object serialization MUST contain at least the
        <spanx style="verb">url</spanx> or <spanx style="verb">items</spanx>
        properties.</t>

      </section>

    </section>

    <section anchor="document" title="The Activity Stream JSON Document">

      <t>The above defined JSON serialization can be used to represent
      activities, objects and media links in any JSON context. This section
      defines one particular use of the above formats to publish a JSON
      document representing a stream of activities.</t>

      <t>Publishers using this format MUST produce a valid JSON document
      whose root value is a <xref target="collection">Collection</xref>.
      This object MUST, at a minimum, include the <spanx style="verb">items</spanx>
      property whose objects MUST be <xref target="activity">Activities</xref>.</t>

    </section>

    <section anchor="id-comparison" title="Comparison of Identifier Values">
      <t>The values of multiple <xref target="object">Object's</xref>
      <spanx style="verb">id</spanx>, <spanx style="verb">upstreamDuplicates</spanx>,
      and <spanx style="verb">downstreamDuplicates</spanx> properties can be
      compared to determine if the objects represent duplicate content.
      Processors MUST compare these values on a character-by-character basis
      (in a case-sensitive fashion).  Comparison operations MUST be based solely
      on the IRI character strings and MUST NOT rely on dereferencing the
      IRIs or URIs mapped from them.</t>

      <t>As a result, two IRIs that resolve to the same resource but are not
      character-for-character identical will be considered different for
      the purposes of identifier comparison.</t>
    </section>

    <section anchor="post-verb" title="The &quot;post&quot; Verb">
      <t>This specification defines one initial verb and defers to other
      specifications to define additional verb and object types as
      defined in <xref target="extensions"></xref>.</t>

      <t>The "post" verb describes the act of authoring an object and then
      publishing it online. The <spanx style="verb">actor</spanx> can be
      any entity; the <spanx style="verb">object</spanx> can be of any
      object type; and the <spanx style="verb">target</spanx>, if specified,
      can be of any object type. A <spanx style="verb">target</spanx>,
      however, is not required.</t>

      <section anchor="implied-activity" title="Implied &quot;post&quot; Activity">

        <t>Because the "post" verb is defined to include the act of publishing
        an object online, it is possible to assume an implied "post" activity
        for any object even if such an activity was never explicitly
        published or received. The properties of this implied activity are as
        follows; any property not explicitly listed here is absent from the
        resulting activity unless the consumer is able to infer a value based
        on out-of-band information outside the scope of this
        specification:</t>

        <t><list style="hanging">
          <t hangText="actor">The <spanx style="verb">actor</spanx>
          of the implied activity is unknown unless the consumer is able
          to infer an <spanx style="verb">actor</spanx> based on information
          outside the scope of this specification. For example, the consumer
          may know via some out-of-band information that all of the objects in
          a particular document were posted by a particular user.</t>

          <t hangText="object">The <spanx style="verb">object</spanx> of the
          implied activity is the object for which this implied activity is
          being constructed.</t>

          <t hangText="verb">The <spanx style="verb">verb</spanx> of the
          implied activity is "post".</t>

          <t hangText="published">The <spanx style="verb">published</spanx>
          of the implied activity is unknown unless the consumer is able to
          infer a time based on information outside the scope of this
          specification.</t>
        </list></t>
      </section>
    </section>

    <section anchor="activity-object" title="The &quot;activity&quot; Object Type">

      <t>The "activity" object type indicates that an Object represents an
      Activity. It can be used whenever an event involving another activity
      is described within an Activity Stream. For instance, when one user
      "shares" or "reposts" an activity from another user.</t>

      <t>In addition to the core Object properties, an "activity" object
      MAY contain any combination of the properties defined for an
      <xref target="activity">Activity</xref>. The values of
      the object's <spanx style="verb">id</spanx> and <spanx style="verb">url</spanx>
      fields MUST match those of the activity being described.</t>

      <t>Note that an <spanx style="verb">activity</spanx> object MUST
      be processable as both an <xref target="object">Object</xref>
      and an <xref target="activity">Activity</xref> and
      may contain fields from either construct, some of which may overlap or
      duplicate content. When duplication of content may occur, an implementation
      SHOULD choose to use the fields from the <xref target="activity">Activity</xref>
      object. For instance, in an <spanx style="verb">activity</spanx> object,
      the Activity's <spanx style="verb">title</spanx> property and the
      Object's <spanx style="verb">displayName</spanx> properties serve
      identical functions, therefore the use of the <spanx style="verb">title</spanx>
      property SHOULD be favored over the use of <spanx style="verb">displayName</spanx>.</t>

      <t>The example below illustrates an activity in which one user, Jane,
      is sharing another activity performed by a second user, John.</t>

<figure><artwork><![CDATA[
  {
    "published": "2011-02-10T15:04:55Z",
    "actor": {
      "objectType" : "person",
      "id": "tag:example.org,2011:jane"
    },
    "verb": "share",
    "object" : {
      "objectType":"activity",
      "title": "John posted a photo",
      "id": "tag:example.org,2011:abc123",
      "verb": "post",
      "actor": {
        "objectType":"person",
        "id":"tag:example.org,2011:john"
      },
      "object": {
        "objectType":"photo",
        "url":"http://example.org/album/my_fluffy_cat.jpg"
      }
    }
  }
]]></artwork></figure>

    </section>

    <section anchor="extensions" title="Extension Object Types and Verbs">
      <t>Other specifications MAY define new object types and verbs for use
      with the concepts and serializations defined in this specification.
      To be clear, new extension properties can be added anywhere in the
      JSON serialization of an object or activity.</t>

      <t>When defining a new verb, the defining specification MUST provide a
      verb identifier for the new verb and MUST define the meaning of the
      verb in terms of the <spanx style="verb">actor</spanx>,
      <spanx style="verb">object</spanx> and <spanx style="verb">target</spanx>
      properties of the activity, and MUST define whether a
      <spanx style="verb">target</spanx> is required and what it
      represents when present.</t>

      <t>When defining a new object type, the defining specification MUST
      provide an object type identifier for the new object type. The
      definition of the new object type MAY define additional properties
      specific to that object type; if so, the specification SHOULD define how
      these additional properties are to be serialized within the JSON document,
      and the specification MAY define how these additional properties are to
      be represented in other serialization formats. The definition of the new
      object type MAY impose additional meaning or constraint on the core
      object properties as long as the new definition remains compatible with
      the definition of the base component.</t>

      <t>Additional extension properties MAY also be defined for
      <xref target="activity">Activities</xref> and
      <xref target="media-link">Media Links</xref>. The
      specification of these properties SHOULD define how they are to be
      serialized within the JSON document, and the specification MAY define
      how they are to be represented in other serialization formats.</t>

      <t>New properties SHOULD be defined such that the
      <xref target="object">Object</xref>,
      <xref target="activity">Activity</xref> or
      <xref target="media-link">Media Link</xref> would remain
      useful if those properties are omitted or removed during processing, to
      enable graceful fallback by consumers that do not implement the
      extension properties or alternative representations that are unable to
      represent the extensions.</t>

      <t>Processors that encounter unfamiliar extension properties within an
      <xref target="object">Object</xref>,
      <xref target="activity">Activity</xref> or
      <xref target="media-link">Media Link</xref> MUST NOT
      stop processing or signal an error and MUST continue processing the
      items as if the extension properties were not present.</t>

    </section>

    <section anchor="other-representations" title="Other Representations">
      <t>This specification defines the primary representation for
      "activities", "objects" and "media links" in terms of the JSON
      serialization format. Other specifications MAY define additional
      serializations of these items. If the new serialization is compatible with
      the JSON data model, the new representation SHOULD be defined as a
      transformation of the raw JSON structures.</t>

      <t>Defining a new representation as a transformation from JSON will
      allow the new representation to automatically support additional
      properties added for new object types as described in <xref
      target="extensions" />. Otherwise the representation of these new
      properties must be defined on a case-by-case basis.</t>
    </section>

    <section anchor="republisher" title="Requirements for Re-publishers">
      <t>A Re-publisher is an agent which receives "activities" or
      "objects" and then transmits these items to other agents.</t>

      <t>When a Re-publisher transmits an "activity", the Re-publisher
      MUST preserve the original <spanx style="verb">verb</spanx>,
      <spanx style="verb">published</spanx>, <spanx style="verb">actor</spanx>,
      <spanx style="verb">object</spanx> and
      <spanx style="verb">target</spanx> properties. The Re-publisher MAY
      preserve the remaining properties, OR the Re-publisher MAY omit these
      properties entirely or replace these properties with locally-determined
      values.</t>

      <t>When a Re-publisher transmits an <spanx style="verb">object</spanx>,
      the Re-publisher MUST maintain the full integrity of the
      <spanx style="verb">object</spanx>, including any extension properties,
      and retain the original <spanx style="verb">id</spanx> value OR, if
      maintaining full fidelity is not possible the Re-publisher MUST assign
      this copy a new <spanx style="verb">id</spanx> and include the
      <spanx style="verb">id</spanx> of the original object as a value
      of the <spanx style="verb">upstreamDuplicates</spanx> property of the
      new copy. In the latter case, a new <spanx style="verb">object</spanx>
      is created which is considered to be a duplicate of the original.</t>
    </section>

    <section anchor="security" title="Security Considerations">
      <t>Publishers or Consumers implementing Activity Streams as a stream of
      public data may also want to consider the potential for unsolicited
      commercial or malicious content and should take preventative measures to
      recognize such content and either identify it or not include it in their
      stream implementations.</t>

      <t>Publishers should take reasonable measures to make sure potentially
      malicious user input such as cross-site scripting attacks are not
      included in the Activity Streams data they publish.</t>

      <t>Consumers that re-emit ingested content to end-users MUST take
      reasonable measures if emitting ingested content to make sure
      potentially malicious ingested input is not re-emitted.</t>

      <t>Consumers that re-emit ingested content for crawling by search
      engines should take reasonable measures to limit any use of their site
      as a Search Engine Optimization loophole. This may include converting
      un-trusted hyperlinks to text or including a rel="nofollow"
      attribute.</t>

      <t>Consumers should be aware of the potential for spoofing attacks
      where the attacker publishes activities or objects with falsified
      property values with the intent of injecting malicious content,
      hiding or corrupting legitimate content, or misleading users.</t>

      <t>Activity Streams are JSON Documents and are subject to the same
      security considerations described in <xref target="RFC4627"/>.</t>

      <t>Activity Streams implementations handle URIs.  See Section 7 of
      <xref target="RFC3986"/>.</t>

      <t>Activity Streams implementations handle IRIs.  See Section 8 of
      <xref target="RFC3987"/>.</t>

    </section>

    <section anchor="iana" title="IANA Considerations">
      <t>None.</t>
    </section>

    <section anchor="license" title="License">
      <t>As of [date], the following persons or entities have made this
      Specification available under the Open Web Foundation Agreement Version
      1.0, which is available at
      <eref target="http://www.openwebfoundation.org/legal/" />.

        <list>
          <t>[List of persons or entities]</t>
        </list>
      </t>

      <t>You can review the signed copies of the Open Web Foundation Agreement
      Version 1.0 for this Specification at
      <eref target="http://activitystrea.ms/licensing/" />, which may also
      include additional parties to those listed above.</t>

      <t>Your use of this Specification may be subject to other third party
      rights. THIS SPECIFICATION IS PROVIDED "AS IS." The contributors expressly
      disclaim any warranties (express, implied, or otherwise), including
      implied warranties of merchantability, non-infringement, fitness for a
      particular purpose, or title, related to the Specification. The entire
      risk as to implementing or otherwise using the Specification is assumed by
      the Specification implementer and user. IN NO EVENT WILL ANY PARTY BE
      LIABLE TO ANY OTHER PARTY FOR LOST PROFITS OR ANY FORM OF INDIRECT,
      SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES OF ANY CHARACTER FROM ANY
      CAUSES OF ACTION OF ANY KIND WITH RESPECT TO THIS SPECIFICATION OR ITS
      GOVERNING AGREEMENT, WHETHER BASED ON BREACH OF CONTRACT, TORT (INCLUDING
      NEGLIGENCE), OR OTHERWISE, AND WHETHER OR NOT THE OTHER PARTY HAS BEEN
      ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.</t>

    </section>

    <section anchor="errata" title="Errata">
      <t>Changes and clarifications to this document are available at
      <eref target="http://activitystrea.ms/specs/json/1.0/errata" />.</t>
    </section>
  </middle>

  <back>
    <references title="Normative References">
      <reference anchor="RFC2119">
        <front>
          <title>Key words for use in RFCs to Indicate Requirement
          Levels</title>

          <author fullname="Scott Bradner" initials="S." surname="Bradner">
            <organization></organization>
          </author>

          <date month="March" year="1997" />
        </front>
      </reference>

      <reference anchor="RFC3986">
        <front>
          <title>Uniform Resource Identifier (URI)</title>

          <author fullname="Tim Berners-Lee" initials="T." surname="Berners-Lee">
            <organization>W3C/MIT</organization>
          </author>

          <author fullname="Roy Fielding" initials="R." surname="Fielding">
            <organization>Day Software</organization>
          </author>

          <author fullname="Larry Masinter" initials="L." surname="Masinter">
            <organization>Adobe Systems</organization>
          </author>

          <date month="January" year="2005" />
        </front>
      </reference>

      <reference anchor="RFC3987">
        <front>
          <title>Internationalized Resource Identifiers (IRIs)</title>

          <author fullname="Martin Duerst" initials="M." surname="Duerst">
            <organization></organization>
          </author>

          <author fullname="Michel Suignard" initials="M." surname="Suignard">
            <organization></organization>
          </author>

          <date month="January" year="2005" />
        </front>
      </reference>

      <reference anchor="RFC4627">
        <front>
          <title>The application/json Media Type for JavaScript Object
          Notation (JSON)</title>

          <author fullname="Douglas Crockford" initials="D."
                  surname="Crockford">
            <organization>JSON.org</organization>
          </author>

          <date month="July" year="2006" />
        </front>
      </reference>

      <reference anchor="RFC3339">
        <front>
          <title>Date and Time on the Internet: Timestamps</title>

          <author fullname="Graham Klyne" initials="G." surname="Klyne">
            <organization></organization>
          </author>

          <date month="July" year="2002" />
        </front>
      </reference>
    </references>

    <section anchor="acknowledgements" title="Acknowledgements">
      <t>The authors wish to thank the Activity Streams community and
      implementers for their support, encouragement, and enthusiasm including
      but not limited to: Abdul Qabiz, Adina Levin, Adrian Chan, Adriana Javier,
      Alan Hoffman, Alex Kessinger, Alexander Ovchinnikov, Alexander Zhuravlev,
      Alexandre Loureiro Solleiro, Amy Walgenbach, Andres Vidal, Angel Robert
      Marquez, Ari Steinberg, Arjan Scherpenisse, Arne Roomann-Kurrik, Beau
      Lebens, Ben Hedrington, Ben Metcalfe, Ben Werdmuller, Benjamin Goering,
      Bill de hÓra, Bo Xing, Bob Aman, Bob Wyman, Brett Slatkin, Brian Walsh,
      Brynn Evans, Charlie Cauthen, Chris Chabot, Chris Toomey, Christian
      Crumlish, Dan Brickley, Dan Scott, Daniel Chapman, Danny Ayers, Dare
      Obasanjo, Darren Bounds, David Cramer, David Nelson, David Recordon,
      DeWitt Clinton, Douglas Pearce, Ed Summers, Elias Bizannes, Elisabeth
      Norris, Eric Marcoullier, Eric Woods, Evan Prodromou, Gee-Hsien Chuang,
      Greg Biggers, Gregory Foster, Henry Saputra, Hillary Madsen, Howard
      Liptzin, Hung Tran, Ian Kennedy, Ian Mulvany, Ivan Pulleyn, Jacob Kim,
      James Falkner, James Pike, James Walker, Jason Kahn, Jason Kantz, Jeff
      Kunins, Jeff Martin, Jian Lin, Johannes Ernst, John Panzer, Jon Lebkowsky,
      Jon Paul Davies, Jonathan Coffman, Jonathan Dugan, Joseph Boyle, Joseph
      Holsten, Joseph Smarr, Josh Brewer, Jud Valeski, Julien Chaumond, Julien
      Genestoux, Jyri Engeström, Kaliya Hamlin, Kevin Marks, Laurent Eschenauer,
      Laurie Voss, Leah Culver, Libby Miller, Manu Mukerji, Mark Weitzel, Marko
      Degenkolb, Marshall Kirkpatrick, Martin Svensson, Marty Alchin, Mary
      Hoder, Matt Leventi, Matt Wilkinson, Matthias Müller-Prove, Max Engel, Max
      Wegmueller, Melvin Carvalho, Michael Buckbee, Michael Chan, Michael
      Richardson, Michael Sullivan, Mike Macgirvin, Mislav Marohnić, Mo Jangda,
      Nate Benes, NeilFred Picciotto, Nick Howard, Nick Lothian, Nissan
      Dookeran, Nitya Narasimhan, Pablo Martin, Pádraic Brady, Pat G.
      Cappalaere, Patrick Aljord, Peter Ferne, Peter Reiser, Peter Saint-Andre,
      Phil Wolff, Philip (flip) Kromer, Richard Cunningham, Richard Zhao, Rick
      Severson, Robert Hall, Robert Langbert, Robin Cover, Ryan Boyd, Sam Sethi,
      Scott Raymond, Scott Seely, Simon Grant, Simon Wistow, Stephen Garcia,
      Stephen Sisk, Stephen Paul Weber, Steve Ivy, Steve Midgley, Steven
      Livingstone-Perez, Sylvain Carle, Sylvain Hellegouarch, Tantek Çelik, Tatu
      Saloranta, Tim Moore, Timothy Young, Todd Barnard, Tosh Meston, Tyler
      Gillies, Zach Copley, and Zach Shepherd.</t>
    </section>
  </back>
</rfc>
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