Formal metadata information and software > CSDGM 1994 (superseded)

Organization of the Standard

This document has been superseded. Everyone should refer instead to the Content Standard for Digital Geospatial Metadata, officially known as FGDC-STD-001-1998, dated June 1998, at the web site of the Federal Geographic Data Committee.

Numbered Sections

The standard is organized in a hierarchy of data elements and compound elements that define the information content for metadata to document a set of digital geospatial data. The starting point is "metadata" (section 0). The compound element "metadata" is composed of other compound elements representing different concepts about the data set. Each of these compound elements has a numbered section in the standard. In each numbered section, these compound elements are defined by other compound elements and data elements. The section "contact information" is a special section that specifies the data elements for contacting individuals and organizations. This section is used by other sections, and is defined once for convenience.

Each section begins with the name and definition of the compound element that defines the section. The name and definition are followed by production rules (see below) that define this compound element in terms of data elements, either directly or by the use of intermediate compound elements. When intermediate compound elements are used, the production rules for these elements also are provided in this part of the section.

The production rules are followed by a list of names and definitions of compound elements and data elements used in the section.

Compound Elements

A compound element is a group of data elements and other compound elements. All compound elements are described by data elements, either directly or through intermediate compound elements. Compound elements represent higher-level concepts that cannot be represented by individual data elements. The form for the definition of compound elements is:
Compound element name -- 0.0.0
definition. Compound.
The type of "compound" uniquely identifies the compound elements in the lists of terms and definitions.

Production Rules

A production rule specifies the relationship between a compound element, and data elements and other (lower-level) compound elements. Each production rule has a left side (identifier) and a right side (expression) connected by the symbol "=", meaning that the term on the left side is replaced by or produces the term on the right side. Terms on the right side are either other compound elements or individual data elements. By making substitutions using matching terms in the production rules, one can explain higher-level concepts using data elements.

The symbols used in the production rules have the following meaning:

is replaced by, produces, consists of
selection - select one term from the list of enclosed terms (exclusive or). Terms are separated by "|".
iteration - the term(s) enclosed is(are) repeated from "m" to "n" times
optional - the term(s) enclosed is(are) optional
a = b + c
"a consists of b and c"
a = [b | c]
"a consists of one of b or c"
a = 4{b}6
"a consists of four to six occurrences of b"
a = b + (c)
"a consists of b and optionally c"
Interpreting the production rules:

Data Elements

A data element is a logically primitive item of data. The entry for a data elements includes the name of the data element, the definition of the data element, a description of the values that can be assigned to the data element. The form for the definition of the data elements is:
Data element name -- 0.0.0
If a data element is described earlier on the same HTML page, the section number is put in parentheses. If the data type is described on another HTML page, a link is given to the page.

The information about the values for the data elements include a description of the type of the value, and a description of the domain of the valid values. The type of the data element describes the kind of value to be provided. The choices are "integer" for integer numbers, "real" for real numbers, "text" for ASCII characters, "date" for day of the year, and "time" for time of the day.

The domain describes valid values that can be assigned to the data element. The domain may specify a list of valid values, references to lists of valid values, or restrictions on the range of values that can be assigned to a data element.

The domain also may note that the domain is free from restrictions, and any values that can be represented by the "type" of the data element can be assigned. These unrestricted domains are represented by the use of the word "free" followed by the type of the data element (that is, free text, free date, free real, free time, free integer).

Some domains can be partly, but not completely, specified. For example, there are several widely used data transfer formats, but there may be many more that are less well known. To allow a producer to describe its data in these circumstances, the convention of providing a list of values followed by the designation of a "free" domain was used. In these cases, assignments of values shall be made from the provided domain when possible. When not possible, providers may create and assign their own value. A created value shall not redefine a value provided by the standard.

Another issue is the representation of null values (representing such concepts as "unknown") in the domain. While this is relatively simple for textual entries (one would enter the text "Unknown"), it is not as simple for the integer, real, date, and time types (for example, which integer value means "unknown"?). Because conventions for providing this information vary among implementations, the standard specifies what concepts shall be represented, but does not mandate a means for representing them.

In addition to the values to be represented, the form of the representation also is important, especially to applications that will manipulate the data elements. The following conventions for forms of values for data elements shall be used:

Calendar Dates (Years, Months, and Days)
Time of Day (Hours, Minutes, and Seconds)
Latitude and Longitude
Network Addresses and File Names
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Maintained by Peter Schweitzer
Last updated 20-Jul-1998