BASE - Bielefeld Academic Search Engine


BASE in General

  • What is BASE?
    BASE (Bielefeld Academic Search Engine) is one of the world's most voluminous search sengines especially for academic web resources, e.g. journal articles, preprints, digital collections, images / videos or research data. Try searching with BASE right now!
  • What is Different about BASE?
    BASE facilitates effective and targeted searches and retrieves high quality, academically relevant results. Other than search engines like Google or Bing BASE searches the deep web as well. The sources which are included in BASE are intellectually selected (by people from the BASE team) and reviewed. That's why data garbage and spam do not occur. Read more details about the project.
  • The People behind BASE
    BASE represents a project of Bielefeld University Library: The BASE Team.
  • BASE Future Developments
    BASE is a strategic project of Bielefeld University and in a state of constant development.
  • Will privacy be guaranteed in BASE?
    All accumulating data which arise while using BASE, are stored exclusively on servers at Bielefeld University and not passed on to third parties. Statistical evaluation is strictly carried out anonymously. For further information see the legal notice.
  • Which indexing software is used for BASE?
    Since May 2011 we are using the open source search technology of Solr/Lucene. Until May 2011 the search engine technology of Microsoft FAST (Fast Search And Transfer) was used.
  • Get in Touch With Us!
    We highly appreciate your comments and feedback. Leave us a message, write a comment in our blog or send a tweet to @BASEsearch.

Indexing New Sources / Documents

  • Which criteria do new sources have to meet to be added to the BASE index?
    There are three criterias: The source has to contain academic content. At least some documents from the source are available as open access (full texts free of charge, without registration). The metadata of the docments are provided via a valid OAI-PMH interface.
  • How can I recommend a new content source?
    Go to the page suggest source and check, if your source is already indexed in BASE and (if it's not indexed) it fits our criterias. After that you can fill out a form and suggest your source to us. We also observe several repository directories like OpenArchives, ROAR and OpenDOAR or repository software directories like DSpace or OJS regularly and harvest and index the content of sources.
  • Can I upload a document directly to BASE?
    No, it's not possible to upload documents to BASE. BASE is not a subject database or a publication management system, but a search engine. To get your publication indexed by BASE you have to upload it to a source (university repository or general repository like Zenodo) or to a journal, which is indexed by BASE (see our list of indexed sources).
  • How do I set up an OAI interface, so that my content source can be indexed by BASE?
    Repository software like DSpace, Eprints oder OJS (for journals) provide an OAI interface by default. Sometimes it has to be activated or configured. Check out our golden rules for repository managers. They might be helpful to optimize your OAI interface. You can also set up an OAI interface on your own. Look for the implementation guideline at the Open Archives Initiative's website. You can find more general information about OAI at and Wikipedia. With our OAI validator OVAL you can easily verify if your source is compliant with the BASE requirements.
  • My source does not provide an OAI interface. Is it possible to index the documents in BASE nevertheless?
    In case your source does not provide an OAI interface, upload your documents to aggregators like DataCite or Zenodo, to subject repositories like RePEC or add your open access journal to DOAJ. We are indexing these sources regularly. However, the best way to get your documents indexed by BASE is to provide an OAI interface - in this case we can assure fast and smooth indexing of your source and data from your source will be presented completely and in the best possible way.
  • Does indexing involves any costs?
    No, all services (including indexing of sources) in BASE are provided without any costs.

Updating / Deleting Content

  • How often do you update the content of indexed sources?
    We are updating all indexed sources twice a month. In larger intervals all content is completely re-harvested and re-indexed.
  • My journal is indexed in BASE. Do I have to send you a message when a new issue is published?
    No, all sources are automatically updated regularly. If an article published in a source, which is already indexed in BASE, won't be indexed after 6 weeks there's usually an issue with the OAI interface of the source. In this case please send us a message with detailed information (at least name and URL of source).
  • I published a document in a source which is indexed in BASE, but I can't find my document in BASE. Why?
    It takes some time until documents added to a source are indexed in BASE, too. If your document won't be indexed after 6 weeks there's usually an issue with the OAI interface of the source. In this case please send us a message with detailed information (at least name and URL of source, title and URL of document).
  • Why are documents from my source not updated?
    Any subsequent change to a record must be marked in your OAI interface by updating the document's datestamp. All indexed sources are regularly updated in BASE. If the "datestamp" is not updated an update in the BASE index is not possible and the document remains unchanged and therefore incorrect in the index until the sources is completely re-indexed, which is only done in largel intervals.
  • Why is my source indexed incorrectly / incompletely?
    It can take up to 6 weeks until a document, which is added to the OAI interface of source, is indexed in BASE. If a source is not updated for a longer time period, this is generally related to an issue with the OAI interface of a source. It might also be the case, that records of a source are provided incorrectly or not at all via the OAI interface of the source. The documents may be provided correctly / completely via the web interface of the source, but as we index OAI-metadata only, the web interface is not relevant for us. You can report errors via our contact form. If you are a manager of a source, please check the compliancy of your source using our OAI validator OVAL and mind our golden rules for repository managers.
  • The name of my source in the field "Content provider" is not correct. Where can I report this?
    If there is a spelling mistake in the name of a content provider or the name of a content provider has changed, you are welcome to report this to us simply via our contact form and we will correct the name as soon as possible.
    Please note: In the field "Content provider" you will always find the name of the source by which we have indexed a document. For various reasons, this may differ from the actual name of your source (e.g. the name of your journal or repository). It is possible that the documents were indexed via an aggregator (e.g. DataCite) or via an e-journal platform. In this case, the name of the aggregator / platform is given. The name of the data provider cannot be changed in this case. For journals, the name of the journal should therefore always be specified in the dc:source field of the OAI interface.
  • Some documents are indexed incorrectly. Where can I report this issue?
    BASE is a search engine. This means, we index the metadata in the way, they are provided by the sources. If you want to change the metadata, you have to correct the data in the source. If the metadata is changed in the OAI interface (and the "Datestamp" of the record is updated, too) it should be updated in BASE, sooner or later, because we update all indexed sources regulary.
  • The percentage of OA documents is not correct for my source. Why are open access documents from my source not marked as open access in BASE?
    In our list or sources we show the percantage of OA documents for every source. There is a three-step process of how a document indexed in BASE gets an open access status:
    1. The content source contains only open access documents. This will be recorded in the BASE-Source database (if known) and all indexed documents of the source are marked open access in BASE
    2. The metadata of an open access document contains a special set for open access documents in <record><header> in "setSpec" (e.g. "driver", "openaire" or "OpenAccess"). This set is entered into our database and all documents from this set are marked as open access.
    3. Open access documents are individually marked by the content provider in <dc:rights> (either CC license or descriptive information such as "OpenAccess" etc.)
    If none of these three details are available, BASE cannot identify the document as open access. If there's an issue with this number, check your OAI interface and improve your metadata, if possible or leave us a message.
  • A source seems to be advertising / spam
    Unfortunately, it can happen that the operator of a source (e.g. a magazine) discontinues his offer and sells the domain. Then it can happen that the new operator offers content that has nothing to do with the original indexed source. As soon as we notice this during a check, the source is deleted immediately. You are welcome to help us by reporting such sources via our contact form.
  • I have deleted a document from my source. Why is it not deleted from BASE?
    If a document is deleted from your source, the record in the OAI interface must be marked as "deleted". Under no circumstances may the record be completely deleted from the OAI interface. If a document is not marked as "deleted" (but instead completely removed from the OAI interface) the document remains unchanged and therefore incorrect in the index until the sources is completely re-indexed, which is only done in largel intervals.
  • My source / document has apparently been removed from BASE. Why that?
    We check all indexed sources regularly. Sources whose servers or OAI interfaces do not work at all or only very unreliably over a longer period of time, or which no longer offer Open Access content, are temporarily or permanently removed from the index. It can also happen that individual documents are no longer made available via the OAI interface of the source. These documents are then also removed from BASE when the source is updated. In this case, check whether the source works correctly and whether the document is still contained in the source itself. If this is the case, you can send us a message using the contact form and ask us to check the source again.

Searching / Result List

  • How do I search BASE?
    See our search help.
  • Do you offer a full text search in the indexed documents?
    Due to time and performance constraints we are indexing only metadata (title, author names, abstract …) of documents. Thus it's not possible to search the full text of the indexed documents.
  • Can I narrow a search on open access content only?
    Use the advanced search and the criteria "Access" to narrow the search on open access documents or exclude documents that are not freely accessible. You can also narrow directly on CC (Creative Commons) licenses. CC licenses allow content to be distributed - there are several sub-licenses, depending on whether commercial retransmission is allowed or retransmission must also be under a CC license. For details see e.g. Wikipedia.
    After performing a search you can narrow your search on open access documents only. To do so, click on "Access" in the "Refine Search Result" box and on "Open Access". The result list will be narrowed on documents, which are clearly marked as open access documents by the data provider in their metadata. Keep in mind that only 40% of all indexed open access documents can be identified as open access because of lack of metadata information (a total of circa 60% of the indexed documents are freely accessible).
  • Why are open access documents in BASE not marked as open access?
    There is a three-step process of how a document indexed in BASE gets an open access status and is marked with an icon (for details, see above). If none of these three details are available, BASE cannot identify the document as open access.
  • Why can't I access the full text of a document?
    About 60% of the indexed documents in BASE are open access, the rest are mere metadata entries without full text or can only be accessed, if you are authorized for accessing this particular source. You can search the metadata of all indexed documents. The authorization is always done by the content provider. If you don't have access to a full text although your institution supposedly is authorized, please contact your IT department or the content provider.
  • Why can't I access a document marked as "Open Access"?
    If a document is marked as "Open Access" but still not accessible, there is usually an error on the part of the data provider. We mark documents as "Open Access" according to the information received from the provider (e.g. corresponding details in the rights information or a CC license). We do not check individually whether this information is correct. If you come across a document that is not correctly labelled as "Open Access", please contact the data provider and point out the problem.
  • Why do I always end up with an error message when I try to access a document?
    If you get an error ("page not found"), the web address (URL) of the document might have changed or the document was deleted since we indexed the source recently. Though content from academic sources should provide permanent addresses and changes or deletion of documents should be communicated via the OAI interface, in practice it's often not the case. Therefore it might happen that links to documents which appear on our result list do not work. Another reason for an error might be, that the server of the content provider is temporarily or permanently not available. If you encounter an error, please leave us a message. We will contact the content provider or remove the content source from our index, if it's a permanent problem.
  • What are metadata?
    Especially in an academic environment you will often come across documents containing metadata. These are descriptive elements assigned to a document in order to specify it both in technical respect and in terms of content. Metadata are for example author's names, publication dates, abstracts, language or - in case of a journal title - details regarding the title or the issue. Sources which we index contain metadata, therefore you can search purposefully for authors or publication years in the advanced search or narrow search results. "Normal" websites generally do not have metadata and this is why a precise search for authors or publication years are not possible or only possible to a very limited extent in internet search engines such as Google or Bing. If metadata are available, you may perform a targeted search for authors. In the result list you may refine the search result by categories.
  • Metadata is broken. Can you correct it?
    If you find a mistake in the metadata, e.g. false or missing author names, titles, years or bugs in the character set (e.g. ? instead of a character) the content providers are responsible for this. We already correct obvious metadata errors with automated procedures during indexing, but a substantive check is impossible. It's best to contact the data provider directly if you find errors in a record.
    If the data record appears correctly at the data supplier, it may be that the data is delivered incorrectly via the OAI interface, which we use to index the data. It may also be that the operator has recently corrected the record. In this case, the data in the BASE results list is also corrected during the next indexing (usually within 1-2 weeks).
  • What does the link "claim" after the author name mean (Add ORCID ID)?
    See information about this topic in the next section.


  • What is ORCID?
    ORCID (Open Researcher and Contributor ID) is a standard for unambiguously matching academic authors to their respective publications that is currently being established worldwide. The ORCID iD as persistent identifier allows, e.g. in case of identical names, name changes or name variants, the clear differentiation of author names. It can be used anywhere in the world and depicts affiliation changes throughout individual academic careers. Thus, it contributes to better visibility of authors and their publications, and more and more publishers and funding organisations are demanding that authors provide an ORCID iD.
  • How can I register with ORCID via BASE, and how can I export publications to ORCID?
    If you are the author of a publication that is listed in a BASE results list, you can confirm the authorship for these publications via the link "claim". For this you must register once with our search engine (see personal login) and have an ORCID iD. If you do not have an ORCID iD yet, you can register for free by clicking on "claim" directly at ORCID. After registering, ORCID will provide you with an ID that allows you to uniquely identify your publications (even if the name is identical to another person, variants in the spelling of your name or name changes). You can also incorporate metadata of the publication (author, title, year of publication, etc.) directly into your publication list at ORCID. After "claiming", an icon ("ID") with a link to your profile at ORCID is displayed next to your your author name in BASE.
  • What is ORCID’s Collect & Connect Program, and what are the badges that BASE was awarded in this program?

    Collect & Connect is ORCID's integration and engagement program, which sets out best practices to clarify implementation goals and expectations across sectors, standardize the user experience, improve understanding of trust in connections between ORCID and other identifiers, increase the efficiency and quality of integrations, and help achieve ORCID's vision through a community approach.

    In the context of ORCID's Collect & Connect program, BASE was awarded the following badges:

    ORCID Collect & Connect badge - Authenticate AUTHENTICATE
    BASE authenticates ORCID iDs to ensure researchers are correctly identified in system.

    ORCID Collect & Connect badge - Display DISPLAY
    BASE displays iDs to signal to researchers that it support the use of ORCID.

    ORCID Collect & Connect badge - Connect CONNECT
    BASE connects information to ORCID records for trusted sharing with others.

BASE Website

  • Why do I always end up on the German-language pages?
    The BASE web pages are presented in the language, which is preselected in your browser settings. These settings can easily be changed (e.g., if you use the Mozilla "Firefox" browser, choose "Preferences" and then "Settings"). Switch to "English" as preferred language and the BASE pages will be presented in English immediately.
  • Is there a print version of the BASE web pages available?
    The BASE web pages are designed to automatically change into a printer optimized version when the printing command is released.
  • Is there an optimized version of the BASE web pages for mobile devices (smartphones etc.) available?
    The BASE pages are designed responsively and therefore always optimally displayed on a large monitor as well as on a tablet or smartphone.
  • Meet the BASE pages web standards?
    The BASE web pages are properly designed to comply with all kinds of browsers and operating systems without any restrictions. The pages are created according to web standards (XHTML, CSS). Older browsers which do not support the latest web standards get a text version without special layout. Great importance was attached to ensuring that the requirements for barrier-free websites according to the BITV (barrier-free information technology regulation) are fulfilled as completely as possible.
  • Why are some words underlined?
    Acronyms and abbreviations,e.g. the word BASE are provided with an explanatory text, the first time they appear in the text of a page. This is displayed when you place the mouse cursor over the word. In order to show where the word has been explained first, the word is shown underlined here.