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5.4.2 Metadata Content and Encoding Standard
Metadata is actually “data about data.” The three distinct types of metadata are
descriptive metadata, structural metadata, and administrative metadata. Descriptive
metadata describes a resource for purposes such as discovery and identification. It
can include elements such as title, abstract, author, and keywords. Structural metadata is the metadata about containers of data and indicates how compound objects
are put together, for example, how pages are ordered to form chapters. It describes
the types, versions, relationships, and other characteristics of digital materials.
Administrative metadata provides information to help manage a resource, such as
when and how it was created, file type and other technical information, and who can
access it (https://en.wikipedia.org/wiki/Metadata).
How metadata information are composed and how each part of it should be
expressed are metadata content and encoding standard. For geolocation information
about agricultural data, ISO 19115, 19115-2, and 19139 are applicable standards that
cover metadata content and encoding. For thematic information about agricultural
data, there are some metadata could be referenced, such as Agricultural Metadata
Element Set (AgMES) published by the Food and Agriculture Organization of the
United Nations (FAO) (http://aims.fao.org/standards/agmes).
In the ISO 19115, the metadata about geospatial information are organized into
12 groups: spatial representation, reference system, metadata extension, constraint,
identification, maintenance, application schema, portrayal catalogue, content, distribution, data quality, and lineage, as depicted in the following figure (Fig. 5.3).
The ISO 19115-2 further defines the metadata for imagery and gridded data. In
particular, it provides information about the properties of the measuring equipment
used to acquire the data, the geometry of the measuring process employed by the
equipment, and the production process used to digitize the raw data. This extension
deals with the metadata needed to describe the derivation of geographic information
from the raw data, including the properties of the measuring system and the
numerical methods and computational procedures used in the derivation. The relationship between metadata contents defined in 19115-2 and those in 19115 is shown
in the figure below (Fig. 5.4).
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Y. Bai