Metadata

Metadata discloses information about the characteristics and properties that describe any entities that allow to automatically search and manage them in large information flows.

The Difference Between Data and Metadata

It is usually impossible to make an unambiguous division into data and metadata in a document because:

Something can be both data and metadata. Thus, the title of an article can be simultaneously referred to as metadata (as a metadata element - the title), and to the actual data (since the title is part of the text itself).
According to the usual definition, metadata is a set of structured information. You can create metadata for metadata, for output to special devices, or read their descriptions using text-to-speech software.

Classification of metadata

Metadata can be classified by

The content. Metadata can either describe the resource itself (for example, the name and size of the file), or the content of the resource (for example, "this video shows how to play football").
The resource as a whole. Metadata can refer to a resource as a whole or to parts of it. For example, "Title" (movie name) refers to the movie, and "Scene description" (the description of the movie episode) is separate for each episode of the film.
Logical inference. Metadata can be divided into three layers: the bottom layer is raw data; middle layer - metadata describing the specified "raw" data; and the top layer is metadata, which allows you to make a logical conclusion using the second layer.

The three most commonly used metadata classes are:

Internal metadata, which describes the structure or constituent parts of a thing. For example, the format and size of the file.
Administrative metadata required for information processing. Such as, information about the author, the editor, the date of publication, etc.
Descriptive metadata that describe the nature of a thing, its attributes. For example, a set of information-related categories, links to other subjects related to the the item in question.

In search engine optimisation SEO-experts concentrate on the concrete part of metadata - HTML-tags:

<title>,< description>,< h1>,< keyword>. It’s the particular examples of metadata.