The XMP Basic Schema contains XMP properties that provide basic descriptive information.

• Exiv2 keys are Xmp.xmp.<Property>
• The schema namespace URI is http://ns.adobe.com/xap/1.0/
• The preferred schema namespace prefix is xmp

Reference: XMP Specification and Documentation

Property	Label	Value type	Exiv2 type	Category	Description
Advisory	Advisory	bag XPath	XmpBag	External	An unordered array specifying properties that were edited outside the authoring application. Each item should contain a single namespace and XPath separated by one ASCII space (U+0020).
BaseURL	Base URL	URL	XmpText	Internal	The base URL for relative URLs in the document content. If this document contains Internet links, and those links are relative, they are relative to this base URL. This property provides a standard way for embedded relative URLs to be interpreted by tools. Web authoring tools should set the value based on their notion of where URLs will be interpreted.
CreateDate	Create Date	Date	XmpText	External	The date and time the resource was originally created.
CreatorTool	Creator Tool	AgentName	XmpText	Internal	The name of the first known tool used to create the resource. If history is present in the metadata, this value should be equivalent to that of xmpMM:History's softwareAgent property.
Identifier	Identifier	bag Text	XmpBag	External	An unordered array of text strings that unambiguously identify the resource within a given context. An array item may be qualified with xmpidq:Scheme to denote the formal identification system to which that identifier conforms. Note: The dc:identifier property is not used because it lacks a defined scheme qualifier and has been defined in the XMP Specification as a simple (single-valued) property.
Label	Label	Text	XmpText	External	A word or short phrase that identifies a document as a member of a user-defined collection. Used to organize documents in a file browser.
MetadataDate	Metadata Date	Date	XmpText	Internal	The date and time that any metadata for this resource was last changed. It should be the same as or more recent than xmp:ModifyDate.
ModifyDate	Modify Date	Date	XmpText	Internal	The date and time the resource was last modified. Note: The value of this property is not necessarily the same as the file's system modification date because it is set before the file is saved.
Nickname	Nickname	Text	XmpText	External	A short informal name for the resource.
Rating	Rating	Closed Choice of Integer	XmpText	External	A number that indicates a document's status relative to other documents, used to organize documents in a file browser. Values are user-defined within an application-defined range.
Thumbnails	Thumbnails	alt Thumbnail	XmpText	Internal	An alternative array of thumbnail images for a file, which can differ in characteristics such as size or image encoding.