Attribute Convention for Data Discovery 1-2 Working

Version and Status

This version is designated as Version 1.2.2.

This page is under development with updated definitions.

Introduction

This page consolidates ongoing work seeking to improve the definitions in the Attribute Convention for Data Discovery (ACDD).

The first 3 sections represent the terms in the corresponding sections of the ACDD.

Modifications relative to the original text may be seen with the history mechanism of this wiki. The original definitions are marked with the Summary keyword Original Definitions.

Process

The edits have been made in this page by anyone in the community who wishes to contribute, and discussed in greater depth in the Discussion page, if necessary.

Once there is some consensus about a group of definitions, they will be migrated to the primary document and the version number of that document incremented.

Status

This summarizes the status of the terms as of 2014.01.31. All major issues have been resolved in the document, pending review by the ACDD team.

Details may be reviewed below the open issues in the Discussion page.

Suggested Changes to introductory words

The following (between § marks) is proposed to replace the text from section Development to just before Highly Recommended. §

Development

Any development version of the ACDD definitions is maintained at Attribute_Convention_for_Data_Discovery_(ACDD)_Working.

Overview

The netCDF metadata model is focused on providing "use metadata" for the data included in the file (or granule). The netCDF Group at Unidata has recommended netCDF attributes for data discovery. This Attribute Convention addresses that need, focusing on attributes that may be most useful to help find data of interest.

Overlap with NetCDF and CF Conventions

The ACDD assumes the NetCDF User Guide (NUG) is being followed; many of ACDD's users also use CF, with which ACDD is compatible. The NUG does not _require_ any global attribute, though it recommends and defines several. ACDD adds recommendations about the title and history attributes of netCDF.

The Climate and Forecast convention adds many more attributes. ACDD adds institution, source, references, and comment, to be either global or assigned to individual variables. When an attribute appears both globally and as a variable attribute, the variable's version has precedence. ACDD does not require or define institution or references.

Attribute Crosswalks

Many of these attributes correspond to general discovery metadata content, so they are available in many metadata standards. This page includes the Unidata crosswalk to THREDDS and adds the crosswalk to ISO 19115-2. Note that the attribute names link to the Unidata definitions. Many of these elements are included in the ISO 19115 Core specification. They are indicated in this Table by an M, O, or C in parentheses. An “M” indicates that the element is mandatory. An “O” indicates that the element is optional. A “C” indicates that the element is mandatory under certain conditions.

== Conformance Test

A Conformance Test is available for this convention.

Additional Metadata: metadata_link attribute

Other metadata dialects (i.e. ISO 19115) can provide information about collections and more details about the dataset. In order to make users aware of that additional metadata we recommend adding a global attribute named "metadata_link" to the netCDF file. The value of this attribute is a URL that gives the location of the more complete metadata. This element is not included in the current version of the NetCDF Attribute Convention for Dataset Discovery.

Global Attributes

_(reformat Highly Recommended, Recommended, etc. as 2nd-level headings)_ §

Working Definitions

Note to be added : The NUG defines title and history to be global attributes. CF adds institution, source, references, and comment, to be either global or assigned to individual variables. When an attribute appears both globally and as a variable attribute, the variable's version has precedence. ACDD does not require or define institution or references.

Highly Recommended

title

A short phrase or sentence describing the dataset; this is a NetCDF Users Guide (NUG) attribute.

summary

A paragraph describing the dataset, analogous to an abstract for a paper.

keywords

A comma-separated list of key words and/or phrases. Keywords may be common words or phrases, terms from a controlled vocabulary (GCMD is often used), or URIs for terms from a controlled vocabulary (see also keywords_vocabulary attribute).

Conventions

A list of the conventions followed by the dataset; blank space separated is recommended but commas should be used if any convention name contains blanks. This attribute is defined in NUG.

source

The method of production of the original data. If it was model-generated, source should name the model and its version. If it is observational, source should characterize it. This attribute is (defined in CF).

Recommended

id

An identifier for the data set, provided by and unique within its naming authority. The combination of the "naming authority" and the "id" should be globally unique, but the id can be globally unique by itself also. IDs can be URLs, URNs, DOIs, meaningful text strings, a local key, or any other unique string of characters. The id should not include blanks.

naming_authority

The organization that provides the initial id (see above) for the dataset. The naming authority should be uniquely specified by this attribute.

cdm_data_type

The organization of the data, as derived from the Common Data Model's Scientific Data layer and understood by THREDDS (this is a THREDDS "dataType"). One of point, profile, section, station, station_profile, trajectory, grid, image, or swath. Please note that this is different from the CF NetCDF attribute 'featureType' that indicates a Discrete Sampling Geometry file - for guidance on those terms, please see this NODC guidance.

history

Describes the processes/transformations used to create this data; can serve as an audit trail. Per the NUG: 'This is a character array with a line for each invocation of a program that has modified the dataset. Well-behaved generic netCDF applications should append a line containing: date, time of day, user name, program name and command arguments.' To include a more complete description you can append an ISO Lineage reference; see NOAA EDM ISO Lineage guidance.

comment

Miscellaneous information about the data, not captured elsewhere.

date_content_modified

The date on which any of the provided content, including data, metadata, and presented format, was last changed (ISO 8601 format)

date_values_modified

The date on which the provided data values were last changed; excludes metadata and formatting changes (ISO 8601 format)

creator

The name of the person principally responsible for originating this data.

creator_email

The email address of the person principally responsible for the data in the file.

publisher

The person responsible for the data file, its metadata and format.

publisher_email

The email address of the person responsible for the data file, its metadata and format.

processing_level

A textual description of the processing (or quality control) level of the data.

acknowledgement

A place to acknowledge various type of support for the project that produced this data.

geospatial_bounds

Describes geospatial extent using any of the geometric objects (2D or 3D) supported by the Well-Known Text (WKT) format.

geospatial_lat_min

Describes a simple lower latitude limit; may be part of a bounding box or cube. Geospatial_lat_min specifies the southernmost latitude covered by the dataset.

geospatial_lat_max

Describes a simple upper latitude limit; may be part of a bounding box or cube. Geospatial_lat_max specifies the northernmost latitude covered by the dataset.

geospatial_lon_min

Describes a simple longitude limit; may be part of a bounding box or cube. Geospatial_lon_min specifies the westernmost longitude covered by the dataset. Cases where geospatial_lon_min is greater than geospatial_lon_max indicate the bounding box extends from geospatial_lon_max, through the longitude range discontinuity meridian (either the antimeridian for -180:180 values, or Prime Meridian for 0:360 values), to geospatial_lon_min.

geospatial_lon_max

Describes a simple longitude limit; may be part of a bounding box or cube. Geospatial_lon_max specifies the easternmost longitude covered by the dataset. Cases where geospatial_lon_min is greater than geospatial_lon_max indicate the bounding box extends from geospatial_lon_max, through the longitude range discontinuity meridian (either the antimeridian for -180:180 values, or Prime Meridian for 0:360 values), to geospatial_lon_min.

geospatial_vertical_min

Describes a numerically smaller vertical limit; may be part of a bounding box or cube. If geospatial_vertical_positive is up ('altitude' orientation), the geospatial_vertical_min attribute specifies the location closest to the earth's center covered by the dataset. If geospatial_vertical_positive is down ('depth' orientation), the geospatial_vertical_min attribute specifies the location furthest from the earth's center covered by the dataset.

geospatial_vertical_max

Describes a numerically larger vertical limit; may be part of a bounding box or cube. If geospatial_vertical_positive is up ('altitude' orientation), the geospatial_vertical_min attribute specifies the location furthest from the earth's center covered by the dataset. If geospatial_vertical_positive is down ('depth' orientation), the geospatial_vertical_min attribute specifies the location closest to the earth's center covered by the dataset.

geospatial_vertical_positive

One of 'up' or 'down'. If up, vertical values are interpreted as 'altitude', with negative values corresponding to below the reference datum (e.g., under water). If down, vertical values are interpreted as 'depth', positive values correspond to below the reference datum.

time_coverage_start

Describes the time of the first data point in the data set. ISO8601 format recommended.

time_coverage_end

Describes the time of the last data point in the data set. ISO8601 format recommended.

time_coverage_duration

Describes the duration of the data set. ISO8601 duration format recommended.

time_coverage_resolution

Describes the targeted time period between each value in the data set. ISO8601 duration format recommended.

license

Provide the URL to a standard or specific license, enter "Freely Distributed" or "None", or describe any restrictions to data access and distribution in free text.

Suggested

The following terms and definitions are offered in case they are applicable to/useful for specific situations.

contributor_info

The name and role of any individuals, projects, or institutions that contributed to the creation of this data. May be presented as free text, or in a structured format compatible with conversion to ncML (e.g., insensitive to whitespace).

date_product_generated

The date on which this product was produced/distributed (ISO 8601 format)

geospatial_lat_units

Units for the latitude axis. These are presumed to be "degree_north"; other options from udunits may be specified instead.

geospatial_lat_resolution

Information about the targeted spacing of points in latitude. (Format is not prescribed.)

geospatial_lon_units

Units for the longitude axis. These are presumed to be "degree_east"; other options from udunits may be specified instead.

geospatial_lon_resolution

Information about the targeted spacing of points in longitude. (Format is not prescribed.)

geospatial_vertical_units

Units for the vertical axis. These are presumed to be "meter" (of depth); other options from udunits may be specified. Note that the common oceanographic practice of using pressure for a vertical coordinate, while not strictly a depth, can be specified using the unit bar.

geospatial_vertical_resolution

Information about the targeted vertical spacing of points.

creator_uri

The unique identifier of the person principally responsible for the data.

creator_institution

The institution that produced the data; should uniquely identify the institution.

creator_institution_info

Additional free text information for the institution that produced the data.

creator_project

The scientific project that produced the data; should uniquely identify the project.

creator_project_info

Additional free text information for the institution that produced the data.

publisher_uri

The unique identifier of the person responsible for the data file, its metadata and format.

publisher_institution

The institution that published the data file; should uniquely identify the institution.

publisher_institution_info

Additional information for the institution that published the data; can include any information as free text, or in a structured format compatible with conversion to ncML (e.g., insensitive to whitespace).

publisher_project

The scientific project that published the data; should uniquely identify the project.

publisher_project_info

Additional information for the institution that published the data; can include any information as free text, or in a structured format compatible with conversion to ncML (e.g., insensitive to whitespace).

keywords_vocabulary

If you are using a controlled vocabulary for the words/phrases in your "keywords" attribute, this is the unique name or identifier of the vocabulary from which keywords are taken. If more than one keyword vocabulary is used, each may be presented with a prefix (e.g., "CF:NetCDF COARDS Climate and Forecast Standard Names") and a following comma, so that keywords may optionally be prefixed with the controlled vocabulary key.

metadata_link

A URI that gives the location of more complete metadata; a URL is recommended.

Deprecated

The following terms and definitions are still in the specification, but are no longer recommended for use.

Metadata_Convention

(deprecated, supported for backward compatibility with current usage) Reference to the particular metadata convention(s) used for the described data file; recommended practice is to add the metadata convention(s) to the comma-delimited conventions list in the 'Conventions' attribute, per NetCDF Best Practices.

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Additional Materials

Mappings ACDD to other metadata dialects

http://wiki.esipfed.org/index.php/Attribute_Convention_for_Data_Discovery_%28ACDD%29_Mappings

Recommended Order of Precedence

http://wiki.esipfed.org/index.php/Attribute_Convention_for_Data_Discovery_%28ACDD%29_Precedence

Future Directions: Object Conventions for Data Discovery

http://wiki.esipfed.org/index.php/Attribute_Convention_for_Data_Discovery_%28ACDD%29_Object_Conventions

ISO Translation Notes

http://wiki.esipfed.org/index.php?title=Attribute_Convention_for_Data_Discovery_(ACDD)_ISO_TranslationNotes