The Library of Congress > Chronicling America > About the Chronicling America API

About the Chronicling America API

Introduction

Chronicling America provides access to information about historic newspapers and select digitized newspaper pages. To encourage a wide range of potential uses, we designed several different views of the data we provide, all of which are publicly visible. Each uses common Web protocols, and access is not restricted in any way. You do not need to apply for a special key to use them. Together they make up an extensive application programming interface (API) which you can use to explore all of our data in many ways.

Details about these interfaces are below. In case you want to dive right in, though, we use HTML link conventions to advertise the availability of these views. If you are a software developer or researcher or anyone else who might be interested in programmatic access to the data in Chronicling America, we encourage you to look around the site, "view source" often, and follow where the different links take you to get started.

For more information about the technical underpinnings of the Chronicling America program, see www.loc.gov/ndnp/.

Please contact us if you have any questions or concerns.

The API

Search the newspaper directory and digitized page contents using OpenSearch.

Link using our stable URL pattern for titles, issues, editions, and pages.

Linked Data views of information about titles, batches, issues, and pages in RDF/XML.

Aggregations of items, like all the pages that make one issue, are related using OAI-ORE.

Searching the directory and newspaper pages using OpenSearch

The directory of newspaper titles contains nearly 140,000 records of newspapers and libraries that hold copies of these newspapers. The title records are based on MARC data gathered and enhanced as part of the NDNP program.

Searching the title records is possible using the OpenSearch protocol. This is advertised in a LINK header element of the site's HTML template as "NDNP Title Search", using this OpenSearch Description document.

Title search parameters:

  • terms: the search query
  • format: 'html' (default), 'json', or 'atom' (optional)
  • page: for paging results (optional)

Examples:

Note that all example URLs below use the same protocol and server name, http://chroniclingamerica.loc.gov/. We only show the URL paths and parameters below to save space.

There are more than a million digitized newspaper pages in Chronicling America. These pages span several decades and many U.S. states and territories. New batches of data come in from partner institutions throughout the year and are added to the site regularly.

Searching newspaper pages is also possible via OpenSearch. This is advertised in a LINK header element of the site's HTML template as "NDNP Page Search", using this OpenSearch Description document.

Page search parameters:

  • andtext: the search query
  • format: 'html' (default), or 'json', or 'atom' (optional)
  • page: for paging results (optional)

Examples:

Link to titles, issues, editions, and pages

The Chronicling America Web site uses links that follow a straightforward pattern. You can use this pattern to construct links into specific newspaper titles, to any of its available issues and their editions, and even to specific pages. These links can be readily bookmarked and shared on other sites.

We are committed to supporting this link pattern over time, so even if we change how the site works, we will redirect any requests to the system using this specific pattern into the new site. We established redirect rules for links into the previous version of the site when we released a new version in early 2009, and we intend to sustain those rules.

The link pattern uses LCCNs, dates, issue numbers, edition numbers, and page sequence numbers.

Examples:

Linked Data

Linked Data allows us to connect the information in Chronicling America directly to related data on the Web explicitly. Chronicling America provides several Linked Data views to make it easy to connect with other information resources and to process and analyze newspaper information with conceptual precision.

We use concepts like Title (defined in DCMI Metadata Terms) and Issue (defined in the Bibliographic Ontology) to describe newspaper titles and issues available in the data. Using these concepts, defined in existing ontologies, can help to ensure that what we mean by "title" and "issue" is consistent with the intent of other publishers of linked data. We also define other concepts not already defined in existing ontologies. This vocabulary includes elements suitable for newspaper information and the NDNP program, including these elements:

  • Awardee
  • Batch
  • Page
  • bag
  • number
  • section
  • sequence

These elements are used in RDF views of several types of pages, ranging from a list of the newspaper titles available on the site and information about each, to enumerations of all the pages that make up each issue and all of the files available for each page.

Examples:

Comparing the RDF versions of the links above with their HTML counterpart links, you might notice that the URI pattern we follow for these views is to remove the final slash, replacing it with ".rdf". We follow this pattern to comply with best practices for publishing linked data, and also to keep the URIs easy to understand and use.

For each of the HTML pages with a linked data counterpart in RDF, we provide links to those alternate views from the HTML page using the LINK header element. This can support automating the process of using the RDF data in tools like bookmarklets, plugins, and scripts, and it also helps us to advertise the availability of the additional views. In many views, such as newspaper page images, we also provide LINK elements pointing to the various available files (image, text, OCR coordinate XML) for each available page or other potentially useful information. We encourage you to explore the entire site and to look for and use these LINK elements if you find them useful when working with NDNP data. Just follow your nose, and view the source.

In addition to the concepts describe above, we use concepts from several other vocabularies in describing NDNP materials and also in linking to related data available on other sites. These additional vocabularies and external sites include:

We are grateful to all of these providers and we hope we can follow their lead in encouraging additional connections between data and vocabulary providers. Please be aware that how we use these vocabularies will likely change over time, as they continue to develop, and as new vocabularies are introduced.

Aggregations

The OAI-ORE specification allows us to define aggregations of resources (pages) on our site that go together as a single unit. For example, we use the OAI-ORE vocabulary to link Page resource to the the JPEG2000, PDF, and OCR files that make them up. Batch, Title and Issue resources are related to Pages using the OAI-ORE vocabluary. You can "view source" on Title, Issue, Page and Batch HTML views, and see that the referenced RDF/XML file is auto-discoverable in a link element as an OAI-ORE Resource Map.