Structured data describes page content in a format that software can process. On a Joomla website, it can explicitly identify an article, organisation, product or breadcrumb trail and their properties.
Vocabulary and syntax
Schema.org defines entity types and properties. For example, Article represents an article and headline describes its heading. JSON-LD, Microdata and RDFa are ways to express this information. A vocabulary and its encoding format are different things.
JSON-LD is placed in a dedicated script block. Microdata and RDFa attach information to HTML elements through attributes. The markup should describe real page content and agree with what visitors can see.
What structured data can provide
Supported markup may make a page eligible for specific enhanced search presentations. Valid syntax does not guarantee that these will appear. Search engines support different features and define their own type and property requirements.
Markup in Joomla
A Joomla component, template and SEO extension may all generate structured data. Before adding another generator, inspect the final HTML. Several blocks can coexist when consistent, but conflicting descriptions of the same entity make maintenance difficult.
After configuring Joomla, check the type, required properties, URLs, language and agreement with the main content. The Schema.org validator helps assess vocabulary and structure. Google Rich Results Test checks the search features it supports. These tests serve different purposes.
Conclusion
Structured data makes page meaning explicit for machines. For Joomla, reliable implementation depends on consistent generators, accurate information and checks of the published output.