How can Open Graph identify publication, modification and expiry times?

Definition: Open Graph identifies an article's publication, last modification and expiry moments with article:published_time, article:modified_time and article:expiration_time. The Open Graph protocol defines all three properties as datetime values attached to an object whose type is article.

Key facts

• The Open Graph protocol defines article:published_time as when an article was first published.
• It defines article:modified_time as when the article was last changed.
• It defines article:expiration_time as when the article is out of date after.
• The protocol's DateTime type contains a date with an optional time component and points to ISO 8601 for its literal form.
• Open Graph places metadata in meta elements in the page head, using property and content attributes.
• RDFa Lite 1.1 lists property among its five attributes and says that both text and URLs can be marked up.

What does each article time field describe?

The three properties describe different moments in an article's lifecycle. article:published_time records the first publication. article:modified_time records the latest change. article:expiration_time marks the point after which the article is out of date. These meanings come from the article section of the Open Graph protocol, which lists the properties under the article object type.

The fields are separate metadata properties. A page can therefore expose a publication moment and a later modification moment, while an expiration moment describes a later boundary for the article's currency. The specification defines what each value means, but does not document how a particular answer engine uses these fields.

How are the fields written in HTML?

The protocol says that authors add extra meta tags in the head. Its structured-property syntax uses property and content, with a colon in the property name for a namespaced property. The article: prefix identifies the article vocabulary used by these fields. The markup shape is:

<meta property="og:type" content="article" />
<meta property="article:published_time" content="1996-12-19T16:39:57-08:00" />
<meta property="article:modified_time" content="1996-12-19T16:39:57-08:00" />
<meta property="article:expiration_time" content="1996-12-19T16:39:57-08:00" />

The three timestamp values in this illustration are examples from RFC 3339. The Open Graph page also lists og:type among the four properties required for every page, alongside og:title, og:image and og:url.

What timestamp form should a value use?

Open Graph defines DateTime as a temporal value made of a year, month and day, with an optional time component. It points to ISO 8601, so a date-only value is within the type described by the protocol. A value with a time component gives more precision for a publication, modification or expiry moment.

RFC 3339 defines an Internet profile of ISO 8601. Its date-time grammar combines a full date, the letter T, and a full time. The time includes hours, minutes and seconds, followed by either Z or a numeric offset such as -08:00. The RFC says that expressed times have a stated relationship to Coordinated Universal Time.

How can you check a page?

Inspect the raw HTML in the document head and look for the meta elements whose property values are the three article: names. Confirm that the page declares og:type as article, then read each value from content. Check that each value represents a date or date and time accepted by the Open Graph DateTime description. For a full timestamp, verify the T separator and the UTC marker or numeric offset described by RFC 3339.

Related terms

• Structured data
• RDFa
• Article structured data
• JSON-LD

FAQ

What is the difference between published time and modified time?

Published time is when the article was first published. Modified time is when it was last changed, according to the Open Graph article properties.

Does expiration time mean that a page is deleted?

No deletion behavior is specified on the Open Graph page. article:expiration_time identifies when the article is out of date after.

Is a clock time required?

No. Open Graph's DateTime description includes a date and an optional time component. A full timestamp can add an offset such as Z or -08:00.

Sources

1. Open Graph protocol, "The Open Graph protocol", undated
2. W3C, "RDFa Lite 1.1 - Second Edition", 17 March 2015
3. IETF, "RFC 3339: Date and Time on the Internet: Timestamps", July 2002

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