Published:
by Wayne Smith
On-page structural schema helps search engines understand a page's hierarchy and its place within the site. It also prompts important considerations about supplemental content:
- What on-site but off-page elements should be treated as supplemental content?
- What authoritative sources are being cited?
- Which entities, topics, or external content are mentioned or discussed?
- What links are highly relevant to the page’s main topic?
Relevance and Supplemental Content
Supplemental content can significantly impact the search queries for which a page is considered relevant. Well-structured and well-supported supplemental content enhances a page’s discoverability and improves its ranking in search engines.
On-Page SEO: Relevance is an Emergent Ranking Factor
Schema markup helps provide clear context to search engines, showing how supplemental content relates to the main content. Just as anchor text adds relevance to a link, supplemental content strengthens the page’s relevance for associated queries.
The on-page schema for supplemental content should specifically reflect its relevance to the page itself. However, the overall relevance of the supplemental content is influenced by all the links and schema data that reference it across the internet.
For example, schema for a citation on a page would only contain information directly relevant to that specific citation, while the original work being cited would typically have a more detailed and comprehensive schema of its own.
Schema Should Be Consistent
Although schema is not a required part of SEO — and search engines can determine relevance through other signals such as links — the information referenced on-page about supplemental content must be consistent with the supplemental content itself.
Statistical Agreement
Fuzzy logic and AI rely heavily on principles of statistical agreement. Similarly, relevance in search engines is largely determined through statistical patterns.
For example, even when considering only links, a resource that receives a higher number of links containing a particular keyword will tend to rank higher for that keyword.
When structuring a site's content, schema for supplemental content should reflect relevance without being overly verbose. The schema on the linking page should support — not compete with — the authority of the supplemental content. In other words, it should complement, not cannibalize, the relevance of the linked resource.
Webpage Supplemental Content Properties
The specifications for schema are open to interpretation. Schema markup defines the structure of the data but does not explicitly dictate how machines should interpret or use that data. As a result, different engineers and systems may implement schema based on their own interpretations. Furthermore, best practices for schema implementation are subject to continuous evolution.
Schema Breadcrumbs
Best practices for breadcrumbs are defined by ARIA and are supported as a search feature by Google and Bing. It is generally inferred that the page above the current page links to the current page. This relationship can be interpreted in such a way that the current page may be crawled before the page above it, potentially speeding up indexing and improving rankings for the current page.
Why ARIA and Schema Breadcrumbs: Examples and Best Practices
Content Clusters
Breadcrumb schema can be used not only with topical clusters but also with content that may not be specifically topically related. In such cases, the hasPart and isPartOf properties can be interpreted as creating topical relationships.
The "mainEntityOfPage" Schema Property
The "mainEntityOfPage" property is often used with breadcrumb schema; Reducing ambiguity around whether a page is a main content page or a supplemental one. It functions similarly to a link, where the value can be a URL or a creative work.
Interpretations of the "mainEntityOfPage" can vary, with some systems treating it as a reference to a single entity, while others may associate it with an abstract topic that includes multiple entities. As a result, a standardized best practice for how this property should be implemented has not yet been established.
Its schema property inverse is "mainEntity" which is indeed a single entity "Thing". It is typically a product page with an offer, however it may also affect search intent and ranking for different query terms.
"hasPart" and "isPartOf" Schema Properties
The "hasPart" and "isPartOf" properties are typically used together to define relationships within a content cluster. The "hasPart" property is placed on the parent page to reference its child pages, while "isPartOf" is used on the child pages to reference their parent page.
On a child page, "isPartOf" should reference the parent page. If the content is about a specific entity, the "mainEntityOfPage" property can still be used in combination.
On the parent page, "hasPart" is used to list and reference the related child pages.
Using "hasPart" does not exclude the use of "mainEntity". On product and e-commerce pages, both can be used together to structure topical and commercial information.
Image, PDF, Video SEO with "hasPart"
Images, PDFs, and Videos can be considered supplemental content. Schema can aid in showing the relevance of non-HTML content types.
Image SEO - Relevancy Optimization
The image "hasPart" schema is part of Google's own documentation and has been well-tested, (it should be considered a best practice). The license and copyright information are used in Google's image search.
Erroneous usage
With "hasPart" and "isPartOf" usage on schema "webPage" these should be paired. If they are not paired, or the crawler is unable to find the reference in the content, then either or both of the pages may not see a ranking benefit. This is based on anecdotal observations not done in scale.
Supplemental content with AI and ChatGPT
AI is evolving how schema is implemented in AI is subject to change with each revision. However, anecdotal observations with ChatGPT show it looks at and follows the "hasPart" and "isPartOf" to formulate answers.
The "mentions" Schema Property
The "mentions" property accepts both a "thing" and a "creativework" the creative work or webpage linked to with content is supplemental content that should be considered by the search engines for ranking based on relevancy.
It infers no linkback from the other page. It provides flexibility for complex topic clusters.
The "citation" Schema Property
The "citation" schema accepts a creative work, subject to interpretation, citations often quote a source that has authority. Such references may be required for YMYL (your money your life) query terms. The schema unambiguously provides the source for the supplemental on-page content.
For YMYL-related query terms, search engines — including AI-driven systems — are increasingly likely to assess whether the sentiment and claims made on-page align with the cited sources. Consistency between the page content and the citation source may become a critical ranking factor.