Common Core Metadata Schema

This section contains guidance to support the use of the common core metadata to list agency datasets and application programming interfaces (APIs) as hosted at agency.gov/data.

Updates to the metadata schema can be found in the changelog. Current metadata version: 1.0 FINAL as of 9/20/13.

Standard Metadata Vocabulary

Metadata is structured information that describes, explains, locates, or otherwise makes it easier to retrieve, use, or manage an information resource (NISO 2004, ISBN: 1-880124-62-9). The challenge is to define and name standard metadata fields so that a data consumer has sufficient information to process and understand the described data. The more information that can be conveyed in a standardized regular format, the more valuable data becomes. Metadata can range from basic to advanced, from allowing one to discover the mere fact that a certain data asset exists and is about a general subject all the way to providing detailed information documenting the structure, processing history, quality, relationships, and other properties of a dataset. Making metadata machine readable greatly increases its utility, but requires more detailed standardization, defining not only field names, but how information is encoded in the metadata fields.

Establishing a common vocabulary is the key to communication. The common core metadata specified in this memorandum is based on DCAT, a hierarchical vocabulary specific to datasets. This specification defines three levels of metadata elements: Required, Required-if (conditionally required), and Expanded fields. These elements were selected to represent information that is most often looked for on the web. To assist users of other metadata standards, mappings to equivalent elements in other standards are provided.

What to Document – Datasets and Web APIs

A dataset is an identifiable collection of structured data objects unified by some criteria (authorship, subject, scope, spatial or temporal extent…). A catalog is a collection of descriptions of datasets; each description is a metadata record. The intention of a data catalog is to facilitate data access by users who are first interested in a particular kind of data, and upon finding a fit-for-purpose dataset, will next want to know how to get the data.

A Web API (Application Programming Interface) allows computer programs to dynamically query a dataset using the World Wide Web. For example, a dataset of farmers markets may be made available for download as a single file (e.g., a CSV), or may be made available to developers through a Web API, such that a computer program could use a ZIP Code to retrieve a list of farmers markets in the ZIP Code area.

The catalog file for each agency should list all of the agency’s datasets that can be made public, regardless of whether they are distributed by a file download or through a Web API. The Endpoint data element is used to indicate which datasets offer Web APIs (see below for more information on Common Core and Extended metadata elements).

Metadata File Format – JSON

The Implementation Guidance available as a part of Project Open Data describes Agency requirements for the development of metadata as per the Open Data Policy. A quick primer on the file format involved:

JSON is a lightweight data-exchange format that is very easy to read, parse and generate. Based on a subset of the JavaScript programming language, JSON is a text format that is optimized for data interchange. JSON is built on two structures: (1) a collection of name/value pairs; and (2) an ordered list of values.

Where optional fields are included in a catalog file but are unpopulated, they may be represented by a null value. They should not be represented by an empty string ("").

The Project Open Data schema is case sensitive. The schema uses a camel case convention where the first letter of some words within a field are capitalized (usually all words but the first one). While it may seem subtle which characters are uppercase and lowercase, it is necessary to follow the exact same casing as defined in the schema documented here. For example:

Correct: contactPoint
Incorrect: ContactPoint
Incorrect: contactpoint
incorrect: CONTACTPOINT

Links to downloadable examples of metadata files developed in this and other formats in the metadata resources. Tools to help agencies produce and maintain their data inventories are available on GitHub and hosted at Labs.Data.gov.

“Common Core” Required Fields

The following “common core” fields are required, to be used to describe each entry:

(Consult the ‘Further Metadata Field Guidance’ section lower in the page to learn more about the use of each element, including the range of valid entries where appropriate. Consult the schema maps to find the equivalent DCAT, Schema.org, and CKAN fields.)

Field Label Definition
title Title Human-readable name of the asset. Should be in plain English and include sufficient detail to facilitate search and discovery.
description Description Human-readable description (e.g., an abstract) with sufficient detail to enable a user to quickly understand whether the asset is of interest.
keyword Tags Tags (or keywords) help users discover your dataset; please include terms that would be used by technical and non-technical users.
modified Last Update Most recent date on which the dataset was changed, updated or modified.
publisher Publisher The publishing entity.
contactPoint Contact Name Contact person’s name for the asset.
mbox Contact Email Contact person’s email address.
identifier Unique Identifier A unique identifier for the dataset or API as maintained within an Agency catalog or database.
accessLevel Public Access Level The degree to which this dataset could be made publicly-available, regardless of whether it has been made available. Choices: public (Data asset is or could be made publicly available to all without restrictions), restricted public (Data asset is available under certain use restrictions), or non-public (Data asset is not available to members of the public)

“Common Core” Required-if-Applicable Fields

The following fields must be used to describe each dataset if they are applicable. U.S. Federal agencies must fill out BureauCode and ProgramCode.

Field Label Definition
bureauCode Bureau Code Federal agencies, combined agency and bureau code from OMB Circular A-11, Appendix C in the format of 015:11.
programCode Program Code Federal agencies, list the primary program related to this data asset, from the Federal Program Inventory. Use the format of 015:001
accessLevelComment Access Level Comment An explanation for the selected “accessLevel” including instructions for how to access a restricted file, if applicable, or explanation for why a “non-public” or “restricted public” data asset is not “public,” if applicable. Text, 255 characters.
accessURL Download URL URL providing direct access to the downloadable distribution of a dataset.
webService Endpoint Endpoint of web service to access dataset.
format Format The file format or API type of the distribution.
license License The license with which the dataset or API is published. See Open Licenses for more information.
spatial Spatial The range of spatial applicability of a dataset. Could include a spatial region like a bounding box or a named place.
temporal Temporal The range of temporal applicability of a dataset (i.e., a start and end date of applicability for the data).

Beyond Common Core – Extending the Schema

“Extensional” and/or domain specific metadata can easily be added using other vocabularies even if it is not a term (entity/property) that will get indexed by the major search engines - it could still be indexed by other custom search engines and by Data.gov. Agencies are encouraged to extend their metadata descriptions using elements from the “Expanded Fields” list shown below, or from any well-known vocabulary (including Dublin Core, FGDC, ISO 19115, NIEM, and a growing number of vocabularies published at Vocab.Data.gov) as long as they are properly assigned.

Expanded Fields

Agencies are encouraged to use the following expanded fields when appropriate. Agencies may freely augment these fields with their own.

Field Label Definition
theme Category Main thematic category of the dataset.
dataDictionary Data Dictionary URL to the data dictionary for the dataset or API. Note that documentation other than a data dictionary can be referenced using Related Documents as shown in the expanded fields.
dataQuality Data Quality Whether the dataset meets the agency’s Information Quality Guidelines (true/false).
distribution Distribution Holds multiple download URLs for datasets composed of multiple files and/or file types
accrualPeriodicity Frequency Frequency with which dataset is published.
landingPage Homepage URL Alternative landing page used to redirect user to a contextual, Agency-hosted “homepage” for the Dataset or API when selecting this resource from the Data.gov user interface.
language Language The language of the dataset.
PrimaryITInvestmentUII Primary IT Investment UII For linking a dataset with an IT Unique Investment Identifier (UII)
references Related Documents Related documents such as technical information about a dataset, developer documentation, etc.
issued Release Date Date of formal issuance.
systemOfRecords System of Records If the systems is designated as a system of records under the Privacy Act of 1974, provide the URL to the System of Records Notice related to this dataset.

Further Metadata Field Guidance (alphabetical by field)

Field accessLevel
Cardinality (1,1)
Required Yes, always
Accepted Values Must be one of the following: “public”, “restricted public”, “non-public”
Usage Notes This field refers to degree to which this dataset could be made available to the public, regardless of whether it is currently available to the public. For example, if a member of the public can walk into your agency and obtain a dataset, that entry is public even if there are no files online. A restricted public dataset is one only available under certain conditions or to certain audiences (such as researchers who sign a waiver). A non-public dataset is one that could never be made available to the public for privacy, security, or other reasons as determined by your agency.
Example {"accessLevel":"public"}
Field accessLevelComment
Cardinality (0,1)
Required Yes, if accessLevel is “restricted public” or “non-public”
Accepted Values String
Usage Notes An explanation for the selected “accessLevel” including instructions for how to access a restricted file, if applicable, or explanation for why a “non-public” or “restricted public” data asset is not “public,” if applicable.
Example {"accessLevelComment":"This dataset contains Personally Identifiable Information and could not be released for public access. A statistical analysis of the data contained herein, stripped of all personal identifiers, is available at http://another.website.gov/dataset."}
Field accessURL
Cardinality (0,1)
Required Yes, if the file is available for public download.
Accepted Values String (URL)
Usage Notes This must be the direct download URL. Use homepage for landing or disambiguation pages, or references for documentation pages. For multiple downloads, use distribution to include as many accessURL entries as you need.
Example {"accessURL":"http://www.agency.gov/vegetables/listofvegetables.csv"}
Field accrualPeriodicity
Cardinality (0,1)
Required No
Accepted Values See usage notes
Usage Notes Must be a value from DCCDAccrualPeriodicity: “Annual”,”Bimonthly”,”Semiweekly”,”Daily”,”Biweekly”,”Semiannual”,”Biennial”,”Triennial”,”Three times a week”,”Three times a month”,”Continuously updated”,”Monthly”,”Quarterly”,”Semimonthly”,”Three times a year”,”Weekly”,”Completely irregular”
Example {"accrualPeriodicity":"Annual"}
Field bureauCode
Cardinality (0,n)
Required Yes, for United States Federal Government agencies
Accepted Values Array of Strings
Usage Notes Represent each bureau responsible for the dataset according to the codes found in OMB Circular A-11, Appendix C. Start with the agency code, then a colon, then the bureau code.
Example The Office of the Solicitor (86) at the Department of the Interior (010) would be: {"bureauCode":["010:86"]}. If a second bureau was also responsible, the format like this: {"bureauCode":["010:86","010:04"]}.
Field contactPoint
Cardinality (1,1)
Required Yes, always
Accepted Values String
Usage Notes -
Example {"contactPoint":"John Brown"}
Field dataDictionary
Cardinality (0,1)
Required No (Documentation that is not specifically a data dictionary belongs in “references”)
Accepted Values String (URL)
Usage Notes -
Example {"dataDictionary":"http://www.agency.gov/vegetables/dictionary.html"}
Field dataQuality
Cardinality (0,1)
Required No
Accepted Values Must be a boolean value of true or false (not contained within quote marks)
Usage Notes Indicates whether a dataset conforms to the agency’s information quality guidelines.
Example {"dataQuality":true}
Field description
Cardinality (1,1)
Required Yes, always
Accepted Values String
Usage Notes This should be human-readable and understandable to an average person.
Example {"description":"This dataset contains a list of vegetables, including nutrition information and seasonality. Includes details on tomatoes, which are really fruit but considered a vegetable in this dataset."}
Field distribution
Cardinality (0,n)
Required No
Accepted Values See Usage Notes
Usage Notes Distribution is a concatenation, as appropriate, of the following elements: accessURL and format. If an entry has only one dataset, enter details for that one; if it has multiple datasets (such as a bulk download and an API), separate entries as seen below:
"distribution": [
        {
            "accessURL":"https://explore.data.gov/views/ykv5-fn9t/rows.csv?accessType=DOWNLOAD", 
            "format":"text/csv"
        }, 
        {
            "accessURL":"https://explore.data.gov/views/ykv5-fn9t/rows.json?accessType=DOWNLOAD", 
            "format":"application/json"
        }, 
        {
            "accessURL":"https://explore.data.gov/views/ykv5-fn9t/rows.xml?accessType=DOWNLOAD", 
            "format":"text/xml"
        }
    ]
Field format
Cardinality (0,1)
Required Yes, if the file is available for public download.
Accepted Values String
Usage Notes This must describe the exact files available at accessURL using MIME Types. [Also note Office Open XML MIME types]
Example {"format":"application/json"}
Field identifier
Cardinality (1,1)
Required Yes, always
Accepted Values String
Usage Notes This field allows third parties to maintain a consistent record for datasets even if title or URLs are updated. Agencies may integrate an existing system for maintaining unique identifiers or enter arbitrary characters for this field. However, each identifier must be unique across the agency’s catalog and remain fixed. Characters should be alphanumeric.
Example {"identifier":"1344"}
Field issued
Cardinality (0,1)
Required No
Accepted Values ISO 8601 Date
Usage Notes Dates should be ISO 8601 of least resolution. In other words, as much of YYYY-MM-DDThh:mm:ss.sTZD as is relevant to this dataset.
Example {"issued":"2001-01-15"}
Field keyword
Cardinality (1,n)
Required Yes, always
Accepted Values Array of strings
Usage Notes Surround each keyword with quotes. Separate keywords with commas. Avoid duplicate keywords in the same record.
Example {"keyword":["vegetables","veggies","greens","leafy","spinach","kale","nutrition"]}
Field landingPage
Cardinality (0,1)
Required No
Accepted Values String (URL)
Usage Notes This field is not intended for an agency’s homepage (e.g. www.agency.gov), but rather if a dataset has a human-friendly hub or landing page that users should be directed to for all resources tied to the dataset. This allows agencies to better specify what a visitor receives after selecting one of the agency’s datasets on Data.gov or in third-party mashups.
Example {"landingPage":"http://www.agency.gov/vegetables"}
Field language
Cardinality (0,n)
Required No
Accepted Values Array of strings
Usage Notes This should adhere to the RFC 5646 standard. This language subtag lookup provides a good tool for checking and verifying language codes. A language tag is comprised of either one or two parts, the language subtag (such as en for English, sp for Spanish, wo for Wolof) and the regional subtag (such as US for United States, GB for Great Britain, MX for Mexico), separated by a hyphen. Regional subtags should only be provided when needed to distinguish a language tag from another one (such as American vs. British English).
Example {"language":["en-US"]} or if multiple languages, {"language":["es-MX","wo","nv","en-US"]}
Field license
Cardinality (0,1)
Required No
Accepted Values -
Usage Notes See list of licenses.
Example {"license":""}
Field mbox
Cardinality (1,1)
Required Yes, always
Accepted Values Email address
Usage Notes -
Example {"mbox":"joe@agency.gov"}
Field modified
Cardinality (1,1)
Required Yes, always
Accepted Values ISO 8601 Date
Usage Notes Dates should be ISO 8601 of least resolution. In other words, as much of YYYY-MM-DDThh:mm:ss.sTZD as is relevant to this dataset. If this file is brand-new, enter the issued date here as well.

If there is a need to reflect that the dataset is continually updated, ISO 8601 formatting can account for this by giving the duration. For instance, P1D for daily, P2W for every two weeks, and PT5M for every five minutes.
Example | {"modified":"2012-01-15"} or {"modified":"P1D"}

Field PrimaryITInvestmentUII
Cardinality (0,1)
Required No
Accepted Values String
Usage Notes Use to link a given dataset with its related IT Unique Investment Identifier, which can often be found in Exhibit 53 documents.
Example {"PrimaryITInvestmentUII":"023-000000001"}
Field programCode
Cardinality (0,n)
Required Yes, for United States Federal Government Agencies
Accepted Values Array of strings
Usage Notes Provide an array of programs related to this data asset, from the Federal Program Inventory.
Example {"programCode":["015:001"]} or if multiple programs, {"programCode":["015:001","015:002"]}
Field publisher
Cardinality (1,1)
Required Yes, always
Accepted Values String
Usage Notes The plaintext name of the entity publishing this dataset.
Example {"publisher":"U.S. Department of Education"}
Field references
Cardinality (0,n)
Required No
Accepted Values Array of strings (URLs)
Usage Notes Enclose each URL within strings. Separate multiple URLs with a comma.
Example {"references":["http://www.agency.gov/legumes/legumes_data_documentation.html"]} or if multiple URLs, {"references":["http://www.agency.gov/legumes/legumes_data_documentation.html","http://www.agency.gov/fruits/fruit_data_documentation.html"]}
Field spatial
Cardinality (0,1)
Required Yes, if the dataset is spatial
Accepted Values See Usage Notes
Usage Notes This field should contain one of the following types of content: (1) a bounding coordinate box for the dataset represented in latitude / longitude pairs where the coordinates are specified in decimal degrees and in the order of: minimum longitude, minimum latitude, maximum longitude, maximum latitude; (2) a latitude / longitude pair (in decimal degrees) representing a point where the dataset is relevant; (3) a geographic feature expressed in Geography Markup Language using the Simple Features Profile; or (4) a geographic feature from the GeoNames database.
Example {"spatial":"Lincoln, Nebraska"}
Field temporal
Cardinality (0,1)
Required Yes, if applicable
Accepted Values ISO 8601 Date
Usage Notes This field should contain an interval of time defined by start and end dates. Dates should be formatted as pairs of {start datetime/end datetime} in the ISO 8601 format. ISO 8601 specifies that datetimes can be formatted in a number of ways, including a simple four-digit year (eg. 2013) to a much more specific YYYY-MM-DDTHH:MM:SSZ, where the T specifies a seperator between the date and time and time is expressed in 24 hour notation in the UTC (Zulu) time zone. (e.g., 2011-02-14T12:00:00Z/2013-07-04T19:34:00Z). Use a solidus (“/”) to separate start and end times.

If there is a need to reflect that the dataset is continually updated, ISO 8601 formatting can account for this with repeating intervals. For instance, updated monthly starting in January 2010 and continuing through the present would be represented as: R/2010-01/P1M.

Updated every 5 minutes beginning on February 15, 2010 would be represented as: R/2010-02-15/PT5M.
Example | {"temporal":"2000-01-15T00:45:00Z/2010-01-15T00:06:00Z"} or {"temporal":"R/2000-01-15T00:45:00Z/P1W"}

Field theme
Cardinality (0,n)
Required No
Accepted Values Array of strings
Usage Notes Separate multiple categories with a comma. Could include ISO Topic Categories.
Examples {"theme":["vegetables"]} or if multiple categories, {"theme":["vegetables","produce"]}
Field title
Cardinality (1,1)
Required Yes, always
Accepted Values String
Usage Notes Acronyms should be avoided.
Example {"title":"Types of Vegetables"}
Field webService
Cardinality (0,1)
Required Yes, if the dataset has an API
Accepted Values String (URL)
Usage Notes This field will serve to delineate the web services offered by an agency and will be used to aggregate cross-government API catalogs.
Example {"webService":"http://www.agency.gov/vegetables/vegetables.json"}

Rationale for Metadata Nomenclature

We sought to be platform-independent and to align as much as possible with existing open standards.

To that end, our JSON key names are directly drawn from DCAT, with a few exceptions.

We added the new accessLevel field to help easily sort datasets into our three existing categories: public, restricted public, and non-public. This field means an agency can run a basic filter against its enterprise data catalog to generate a public-facing list of datasets that are, or could one day be, made publicly available (or, in the case of restricted data, available under certain conditions). This field also makes it easy for anyone to generate a list of datasets that could be made available but have not yet been released by filtering accessLevel to public and accessURL to blank.

We added the new accessLevelComment field for data stewards to explain how to access restricted public datasets, and for agencies to have a place to record (even if only internally) the reason for not releasing a non-public dataset.

We added the new systemOfRecords field for data stewards to optionally link to a relevant System of Records Notice URL. A System of Records is a group of any records under the control of any agency from which information is retrieved by the name of the individual or by some identifying number, symbol, or other identifier assigned to the individual.

We added the new bureauCode field to ensure every dataset is connected in a standard way with an agency bureau.

We added the new programCode field to ensure that when applicable, every dataset is connected in a standard way with an agency program office.

We added the new dataQuality to indicate whether or not the data meets an agency’s Information Quality Guidelines.

Additional Information