The form for the definition of the data elements is:
- Data element name -- definition.
- Type:
- (choice of "integer", "real", "date", or "time")
- Domain:
- (describes valid values that can be assigned)
- Short Name:
- (short name consisting of eight alphabetic characters or less)
Short names consisting of eight alphabetic characters or less are included to assist in implementation of the standard.
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.
An example of the definition of a data element is:
- Abstract -- a brief narrative summary of the data set.
- Type:
- text
- Domain:
- free text
- Short Name:
- shortnam
The domain of values for a data element:
- may be specified only by type. Any values that can be
represented by the type of the data element can be assigned. These
domains are represented by the use of thewrod "free" followed by the
type of the data element (that is, free integer, free real, free text,
free date, free time). For example:
- Abstract -- a brief narrative summary of the data set.
- Type:
- text
- Domain:
- free text
- Abstract -- a brief narrative summary of the data set.
- may be specified by a list of values, references to a list of
values, or a range of values. The value assigned must be selected
from the domain. For example:
- Progress -- the state of the data set.
- Type: text
- Domain: "Complete" "In work" "Planned"
- Type: text
- Progress -- the state of the data set.
- may be partly specified by a set of values, followed by the "free"
convention. The value assigned should be from the domain if possible.
If a needed value is not available, providers may create and assign their
own value. For example:
- Depth Distance Units -- units in which depths are recorded.
- Type: text
- Domain: "meters" "feet" free text
- Type: text
- Depth Distance Units -- units in which depths are recorded.
Forms for Special Values
The form of the representation of data values is important to applications that will manipulate the data elements. This importance is especially true for metadata provided through the National Geospatial Data Clearinghouse. If the values are provided in a standard way, "client" software can help a user to evaluate data.
The following conventions for forms of values for data elements shall be used with the metadata standards:
- Calendar Dates (Years, Months, and Days)
-
- A.D. Era to December 31, 9999 A.D. -- Values for day and month of year, and for years, shall follow the calendar date convention (general forms of YYYY for years; YYYYMM for month of a year (with month being expressed as an integer), and YYYYMMDD for a day of the year) specified in American National Standards Institute, 1986, Representation for calendar date and ordinal date for information interchange (ANSI X3.30-1985): New York, American National Standards Institute (adopted as Federal Information Processing Standard 4-1).
- B.C. Era to 9999 B.C. -- Values for day and month of year, and for years, shall follow the calendar date convention, preceded by the lower case letters "bc" (general forms of bcYYYY for years; bcYYYYMM for month of a year (with month being expressed as an integer), and bcYYYYMMDD for a day of the year).
- B.C. Era before 9999 B.C. -- Values for the year shall consist of as many numeric characters as are needed to represent the number of the year B.C., preceded by the lower case letter "cc" (general form of ccYYYYYYY...).
- A.D. Era after 9999 A.D. -- Values for the year shall consist of as many numeric characters as are needed to represent the number of the year A.D., preceded by the lower case letter "cd" (general form of cdYYYYYYY...).
- Time of Day (Hours, Minutes, and Seconds)
-
- Because some geospatial data and related applications are
sensitive to time of day information, three conventions are permitted.
Only one convention shall be used for metadata for a data set. The
conventions are:
- Local Time. For producers who wish to record time in local time, values shall follow the 24-hour timekeeping system for local time of day in the hours, minutes, seconds, and decimal fractions of a second (to the precision desired) without separators convention (general form of HHMMSSSS) specified in American National Standards Institute, 1986, Representations of local time of day for information interchange (ANSI X3.43-1986): New York, American National Standards Institute (adopted as Federal Information Processing Standard 58-1).
- Local Time with Time Differential Factor. For producers who wish to record time in local time and the relationship to Universal Time (Greenwich Mean Time), values shall follow the 24-hour timekeeping system for local time of day in hours, minutes, seconds, and decimal fractions of a second (to the resolution desired) without separators convention. This value shall be followed, without separators, by the time differential factor. The time differential factor expresses the difference in hours and minutes between local time and Universal Time. It is represented by a four-digit number preceded by a plus sign (+) or minus sign (-), indicating the hours and minutes the local time is ahead of or behind Universal Time, respectively. The general form is HHMMSSSSshhmm, where HHMMSSSS is the local time using 24-hour timekeeping (expressed to the precision desired), 's' is the plus or minus sign for the time differential factor, and hhmm is the time differential factor. (This option allows producers to record local time and time zone information. For example, Eastern Standard Time has a time differential factor of -0500, Central Standard Time has a time differential factor of -0600, Eastern Daylight Time has a time differential factor of -0400, and Central Daylight Time has a time differential factor of -0500.) This option is specified in American National Standards Institute, 1975, Representations of universal time, local time differentials, and United States time zone reference for information interchange (ANSI X3.51-1975): New York, American National Standards Institute (adopted as Federal Information Processing Standard 59).
- Universal Time (Greenwich Mean Time). For producers who wish to record time in Universal Time (Greenwich Mean Time), values shall follow the 24-hour timekeeping system for Universal Time of day in hours, minutes, seconds, and decimal fractions of a second (expressed to the precision desired) without separators convention, with the upper case letter "Z" directly following the low-order (or extreme right hand) time element of the 24-hour clock time expression. The general form is HHMMSSSSZ where HHMMSSSS is Universal Time using 24-hour timekeeping, and Z is the letter "Z". This option is specified in American National Standards Institute, 1975, Representations of universal time, local time differentials, and United States time zone reference for information interchange (ANSI X3.51-1975): New York, American National Standards Institute (adopted as Federal Information Processing Standard 59).
- Because some geospatial data and related applications are
sensitive to time of day information, three conventions are permitted.
Only one convention shall be used for metadata for a data set. The
conventions are:
- Latitude and Longitude
-
- Values for latitude and longitude shall be expressed as decimal
fractions of degrees. Whole degrees of latitude shall be represented by a
two-digit decimal number ranging from 0 through 90. Whole degrees of
longitude shall be represented by a three-digit decimal number ranging from
0 through 180. When a decimal fraction of a degree is specified, it shall be
separated from the whole number of degrees by a decimal point. Decimal
fractions of a degree may be expressed to the precision desired.
- Latitudes north of the equator shall be specified by a plus sign (+), or by the absence of a minus sign (-), preceding the two digits designating degrees. Latitudes south of the Equator shall be designated by a minus sign (-) preceding the two digits designating degrees. A point on the Equator shall be assigned to the Northern Hemisphere.
- Longitudes east of the prime meridian shall be specified by a plus sign (+), or by the absence of a minus sign (-), preceding the three digits designating degrees of longitude. Longitudes west of the meridian shall be designated by minus sign (-) preceding the three digits designating degrees. A point on the prime meridian shall be assigned to the Eastern Hemisphere. A point on the 180th meridian shall be assigned to the Western Hemisphere. One exception to this last convention is permitted. For the special condition of describing a band of latitude around the earth, the East Bounding Coordinate data element shall be assigned the value +180 (180) degrees.
- Any spatial address with a latitude of +90(90) or -90 degrees will specify the position at the North or South Pole, respectively. The component for longitude may have any legal value.
- Values for latitude and longitude shall be expressed as decimal
fractions of degrees. Whole degrees of latitude shall be represented by a
two-digit decimal number ranging from 0 through 90. Whole degrees of
longitude shall be represented by a three-digit decimal number ranging from
0 through 180. When a decimal fraction of a degree is specified, it shall be
separated from the whole number of degrees by a decimal point. Decimal
fractions of a degree may be expressed to the precision desired.
- Network Addresses and File Names
-
- Values for file names, network addresses for computer systems, and related services should follow the Uniform Resource Locator convention of the Internet when possible. See http://www.ncsa.uiuc.edu/demoweb/url-primer.html for additional details about the Uniform Resource Locator.
