Interoperability: Linked Data & OpenArchives API
The Hellenic Aggregator of Scientific Content OpenArchives.gr now has two new ways of publishing data. The Web API allows third-party applications to search for and display data aggregated here. Linked Data is a publishing approach which allows data integration and use.
OpenArchives.gr uses Europeana Data Model (EDM) for the documentation of the digital assets it aggregates. EDM is an RDF model advocated by Europeana for the representation of digital content metadata.
Metadata in OpenArchives.gr retain semantic links to other data - vocabularies and thesauri- also offered as Linked Data using RDF links to specific EDM model traits. EKT enriched items with links to the Typology Vocabulary that we developed, which in turn links to the Getty Art & Architecture Thesaurus (AAT) and the semantic thesaurus DBpedia of Wikipedia.
Items have unique, permanent HTTP URIs so that they can be referred to by users and applications. An example of a URI is the one below:
https://www.openarchives.gr/aggregator-openarchives/edm/eureka/000008-10184_8264.
Each item’s URI give us its descriptive metadata in 3 different formats:
When a user enters an item’s URI to a common browser he/she will see the HTML item page. The same HTML page will be shown to an HTTP/REST Client if the command includes the value “text/html” in the header parameter “Accept”.
If a HTTP/REST Client submits a URI with the value "application/rdf+xml" or "application/xml" in the header parameter “Accept”, he/she will get the RDF item description- according to EDM- in RDF/XML serialization. Alternatively, they can use the ending "/xml" in the URI with no need to define the “Accept” parameter.
Finally, by using the value "application/ld+json" or "application/json" in the Header parameter "Accept", the RDF (modelled in EDM) description of the item will be viewed in JSON ( JSON-LD in particular) serialization. Alternatively, they can use the ending "/json" at the item’s URI with no need to define the "Accept" parameter.
OpenArchives.gr has a web API that allows third-party applications to search for and view documents hosted by the aggregator. The API offers all the search capabilities provided by the web portal.
To use the API one has to apply for a personal API Key via this form.
The API’s basic URI is the following:
https://www.openarchives.gr/aggregator-openarchives/api/search.json
You can test the OpenArchives API and the item HTTP URI dereference via the Swagger GUI.
| Name | Datatype | Description | Mandatory | |
|---|---|---|---|---|
| apiKey | String | The API key which allows one to use the API. To obtain it one has to apply through our form. | Yes | |
| general_term | String | Generic term which will be queried across all metadata fields. Search function is “fuzzy search” which gives results based on unfinished words or phrases. | No | |
| ekt_type | Array(String) | Term from the Vocabulary of Types developed by EKT. Search is based on the “EKT Type” metadata field, which EKT added as part of our semantic enrichment workflow applied to all aggregated content. In the default mode, the suggested names of each term should be used in Greek or in English, provided that the preferredLanguage parameter is "en". Alternatively, the URIs of the terms can be used if the ektFieldsUseURIs parameter has a "false" value. The ekt_type parameter is multiple, meaning that more than one type can be given (eg .. & ekt_type=Article & ekt_type=Journal part). In this case, logical coupling (OR) is used, that is, documents that have at least one of the given formulas will be returned. | No | |
| ekt_chronology | String | The chronology of creation of an item as year (ie 1970) or timespan (ie 1990/2000). Search is based on the field “EKT Chronology” which EKT added as part of our semantic enrichment workflow applied to all aggregated content. | No | |
| ektFieldsUseURIs | Boolean | When the parameter has “false” value (default), the values for parameter ekt_type are the suggested terms (in Greek or English depending on the value of parameter preferredLanguage). When the parameter has “true” value, the values for parameter ekt_type are the terms’ URIs. Default value: false |
No | |
| dc_type | String | Search original item type (dc:type) used by the owner institution. Search function is “fuzzy search” which gives results based on unfinished words or phrases. | No | |
| dc_subject | String | Search subject (dc:subject) used by the owner institution. Search function is “fuzzy search” which gives results based on unfinished words or phrases. | No | |
| dc_creator_or_dc_contributor | String | Search creator (dc:creator) or contributor (dc:contributor) used by the owner institution. Search function is “fuzzy search” which gives results based on unfinished words or phrases. | No | |
| dcterms_spatial | String | Search geographical coverage (dcterms:spatial) used by the owner institution. Search function is “fuzzy search” which gives results based on unfinished words or phrases. | No | |
| institution | String | Search items by a specific institution. Acceptable values in this parameter are the official names of institutions in Greek or English as they appear here and here, respectively, depending on the value of parameter preferredLanguage. | No | |
| collection | String | Search items of a specific collection. Acceptable values in this parameter are the official names of collections in Greek or English as they appear here and here, respectively, depending on the value of parameter preferredLanguage. | No | |
| preferredLanguage | String | Suggested language with acceptable values "el" (Greek) ή "en" (English). The parameter defines which language the parameter ekt_type, ekt_historical_period, institution and collection values should be. It also defines the language of the values of the respective fields in the search results. Default value: el |
No | |
| page | Number | Results are paginated with each page consisting of up to 50 entries. This parameter defines the corresponding page. Default value: 1 |
No |
Τhe response to the OpenArchives API is always formatted in JSON SearchAPIBriefItem and will contain a number of fields that present information about the handling of the request, while the concrete information about the record is presented in the "items" field SearchAPIBriefItem corresponding with the items. Results are paginated with each page consisting of up to 50 entries. Each item SearchAPIBriefItem includes only some of the metadata fields and the thumbnail URL. It does include the HTTP URI of the item which can be used for obtaining the full item description (as EDM in XML/RDF serialization, as EDM in JSON-LD serialization or as HTML)
| Field | Datatype | Description |
|---|---|---|
| apiKey | String | The authentication parameter sent out by the client |
| totalResults | Number | The total number of results |
| page | Number | The page number |
| pageSize | Number | Number of results per page |
| results | Array(SearchAPIBriefItem) | This is a collection of search results SearchAPIBriefItem corresponding to the items |
| Field | Datatype | Description |
|---|---|---|
| uri | String | The HTTP URI of the item. It can be used to retrieve the full description of the item as EDM in XML / RDF serialization, as EDM in JSON-LD serialization or as HTML. |
| dc_title | Array(String) | The title of the item. Corresponds to the dc:type property of EDM. |
| ekt_type | Array(String) | ΕΚΤ type from the Vocabulary of Types. It has been added by EKT as part of the semantic enrichment it applies to the content it accumulates. |
| ekt_chronology | Number | ΕΚΤ chronology. It has been added by EKT as part of the semantic enrichment it applies to the content it accumulates. |
| dc_creator | Array(String) | The creator of the item. It matches the dc:creator property of EDM. |
| dc_contributor | Array(String) | The factor of the item. Corresponds to the dc:contributor property of EDM. |
| journalName | String | The name of the Journal (if this item is a Journal article or issue) |
| conferenceName | String | The name of the Conference (if this item is a Conference article or proceedings) |
| aggregator | String | The Content Aggregator that provides the item (OpenArchives.gr) |
| institution | String | The institution holding the item. |
| collection | String | The collection the item originates from. |
| edm_isShownAt | String | The URL of the item page in the institution's repository site. |
To obtain an API key just fill in the form below. As soon as your registration application is authenticated by the OpenArchives.gr team you shall receive an email with the API key.
The use of the OpenArchives.gr API is conditioned upon the unreserved acceptance of the Terms of Use (ToU) described henceforth and is construed as an acceptance of these Terms of Use.
