To achieve this common understanding, a number of characteristics, or attributes of the data have to be defined, also known as metadata.
[5] A good example of metadata is the cataloging system found in libraries, which records for example the author, title, subject, and location on the shelf of a resource.
Another is software system knowledge extraction of software objects such as data flows, control flows, call maps, architectures, business rules, business terms, and database schemas.
Many current schemas use Standard Generalized Markup Language (SGML) or XML to specify their syntax.
Many different metadata schemas are being developed as standards across disciplines, such as library science, education, archiving, e-commerce, and arts.