Like “entity“, the word “attribute” has a specific technical sense when used in the SGML context, which differs somewhat from its sense when used in the database design context. An SGML attribute is a category of information associated with a particular type of element, but not contained within it. Attributes are associated with particular element occurrences by including their name and value within the start-tag for the element concerned. For example:
Call me <name type="Biblical">Ishmael</name>.
Here “type” is the name of an attribute associated with any occurrence of the <name> element, “Biblical” is the value defined for this attribute in the case of the example <name> above.
Attributes are used for two related purposes: they enable an identifying number or name to be associated with a particular element occurrence within a text (which might otherwise be missing), and they enable additional information missing from a text to be added to it without violating its integrity (Burnard 1991, §4.3).