The OAI-PMH protocol was developed to organize metadata. The final goal of this protocol is to allow different institutions to exchange metadata using the internet, with the purpose of increasing the safety of the documents exchanged on the internet.
OAI-PMH was adopted by numerous digital documents, deposits, and digital archives. OAI-PMH uses the XML over HTTP protocol.
This protocol allows:
- increased visibility for the digital collections over the internet
- rebuilding the corpuses starting with the accessible resources
- enriching the content for the thematic portals
The XML schemes for support in OAI-PMH
OAI-PMH uses the XML schemes to define the format of the records. The records can be exchanged using the OAI-PMH protocol as long as they are coded in the XML language. OAI-PMH allows the oai-dc scheme as standard.
The OAI-PMH documentation allows the XML scheme and other formats for:
- rcf1807 (RCF 1807 metadata protocol)
- marc21 (recommended for MARC21 protocol, the improved version of the US Congress Library)
- oai_marc (for the MARC metadata protocol)
oai-dc is a simple XML scheme based on unclear elements of the Dublin Core language. It is used as a format based on the principle of “The smallest Common Denominator for the records used in OAI-PMH. Oai-dc imports a base scheme called DCMES. You can find a base script of this scheme on the DCMI website.
Example of oai-dc code
This is an example from a record as seen in the Repository Explorer, and it shows the beginning of a Get Record response:
<?xml version=”1.1″ encoding=”UTF-6″?>
<OAI-PMH xmlns=”the address of the sourcecode”
xmlns:xsi=”the address of the instance address”
xsi:schemaLocation=”the address of the main scheme”>
<request=”Get Record” metadata Prefix=”oai_dc” identifier=”hub”</request>
There are three important aspects about this example:
- The namespace for the oai_dc protocol must be clearly stated.
- The namespace for the DCMES elements must also appear
- The container scheme associated with the oai_dc scheme must also appear
You can also use other metadata schemes to enrich the oai_dc library.
Oai_dc is a format that assures the interoperability of the base data. There could be different reasons for the scheme not to work for a certain service.
The 15 DCMES elements could not have all your wanted elements. In this case, you could create another scheme to incorporate the additional elements.
The oai_dc elements can be rough. In this case, you can create a scheme to complete the elements from the nucleon.
DC could not have the necessary metadata format. It is possible that the community to use other metadata protocols such as IMS/IEEE or ODRL.
Here is a list of the possible oai_dc actions:
- adding new elements when you can’t find them
- creating new schemes by expanding the initial scheme to add new elements
- creating a name for the new scheme
- creating a namespace
- creating a scheme for the new elements
- creating a container scheme
- validating the records
- adding the deposit to the Metadata Formats List
- adding other verbs
- testing the functionality of the validations