itemId vs sameAs vs additionalType: how to distinguish and use correctly

One of the best methods to gain the topical relevance of a text is to use entities instead of "plain" keywords. The most simple way to create an entity out of a keyword is to extend it as a standalone type with the Schema.org-markup and prove it with additional trustful informations. Here is the applying point of HTML5 attribute itemId and Schema.org-properties sameAs and additionalType. All of them are used to provide additional informations to a type. But while itemId and sameAs are pretty much the same, additionalType is used for different purpose. Let's look at the use cases in detail to get clear about distinguishing and correct assignment. Accurate usage of these properties is crucial for semantic SEO purposes, cause the kind of the entity creation turns the algorithms opinion about the given text to finally more or less topical ranking.
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September 02, 2014